Dr Gerald Darwin Kuhn (1931-2011) led the team that authored the first ever USDA Complete Guide in 1988.
He was a pioneer in the 1970s and 1980s in establishing the USDA’s modern approach to research-based home canning.
He led a team that would sort through 100 years of canning advice and keep only what passed rigorous safety testing. He believed that it was possible through rigorous scientific testing to provide home canners with iron-clad safety guarantees when they followed tested recipes: something we now take for granted.
Kuhn was born in Bourbon, Indiana to Elmer and Hester Grosvenor Kuhn on 15 April 1931. There were 8 children in the family.
He was educated in Indiana, receiving his B.S., M.S. and Ph.D. degrees at Purdue University in West Lafayette, Indiana.
In 1953 to 1955, he was stationed in Korea with the US army.
In 1960, at the age of 29, he joined the faculty at the University of Florida.
In 1962, he married Maxine Barker in Gainsville, Florida. The couple would have 4 children.1
In 1967, the young family moved to Pennsylvania when Kuhn accepted an offer at Penn State with the encouragement of Dr Thomas King.
There, he became an associate professor of Food Technology.2
In 1968, he was listed as an Extension Food Technologist with Penn State:
Area Marketing Agent Larry Yager reported attending the annual meeting of the Interstate Milk Producers Cooperative in Philadelphia, a roadside marketing conference in Ohio and a Saleable Crafts Workshop at Penn State. He reported contacting local fruit processors in regard to quality control procedures, working in company with Dr. Gerald Kuhn, Extension Food Technologist.”3
In 1970, he was cited as being with the Department of Horticulture:
Penn State College of Agriculture faculty members also presenting topics are: B. Wayne Kelly, Extension farm management specialist; Dr. Donald H. Petersen, Extension plant pathologist; and Dr. C. M. Ritter, Dr. Cyril B. Smith, Dr. Loren D. Tukey, Dr. Chester W. Hitz, George M. Greene II and Gerald D. Kuhn, all of the Department of Horticulture.4
Early work with home canning
Kuhn’s first reported association with home canning directly dates from the start of the 1970s, just as Kuhn was entering his 40s.
In 1971, he is cited for an article on pickles:
Usual color changes in home processed pickles occurs because vinegar changes the acidity, which in turn affects the color of the pickles. The higher the acidity the greater the color change. And when garlic is added to cucumber pickles a more noticeable color change may occur. Gerald Kuhn, extension food technologist at the Pennsylvania State University, says that this color change in no way causes an inferior product. Read the label on the vinegar you buy to find out what percent acidity it is. Vinegar acid strengths vary from 4 to 6 per cent. If you are unable to buy the strength recommended in your recipe, calling for 4 per cent acetic acid would require only two-thirds of the 6 per cent acetic acid to obtain the same acidity.”5
By 1973, he was presenting to the public on safety in home canning.
This week, host Gene Stanley will be talking to Penn State Extension food technologists Gerald Kuhn, Morris Mast, and William Jones about the microbiological hazards of food. The discussion begins on Monday when Dr. Gerald Kuhn presents an overview of the microbiological hazards of food and how they relate to the consumer. On Tuesday, Dr. Morris Mast discusses various types of bacteria related to food poisoning and describes how a laboratory tests possibly contaminated food. Dr. Mast is joined on Wednesday by Dr. William Jones for some consumer tips on selection, handling, storage, and preparation of food from the supermarket to the kitchen and, finally, an outdoor picnic. Botulism, a rare type of food poisoning, is the subject of Thursday’s “Farm, Home and Garden” program, when Gene Stanley and Dr. Kuhn examine food related to botulism poisoning and how it can be prevented through proper home canning techniques.6
An article from the Gettysburg Times in 1974 shows that Kuhn was paying close attention to safety practices in the commercial canning industry:
Today’s processed foods are probably safer than ever before, says Dr. Gerald D. Kuhn, Extension food technologist at The Pennsylvania State University. Dr. Kuhn points out that out of more than 775 billion cans of commercially produced food during the last 48 years in the United States, only four deaths due to botulism have occurred. This safety record can be compared to nearly 700 deaths in the same 48 years caused by eating botulism toxin in home canned foods.
Intensive research, sponsored by the canning industry and public health authorities during the late 1920s, resulted in improved canning methods quickly adopted by the canning industry. These improved processing methods were based on scientific data that specified the time and temperature needed to sterilize specific food products of specific styles in specific-sized containers. Applying these principles eliminates the botulism toxin from forming, explains Dr. Kuhn.
Investigations of each of the four botulism deaths that did occur in the last 48 years revealed that causes were due either to faulty container seals, faulty heat processing equipment or not heating the product properly. Many recent food recalls were due to the use of newer canning equipment which caused an unsuspected lowering of the heat penetration rate through the can contents during processing. This resulted in under-sterilization. Recent preventive food processing regulations, passed by the Food and Drug Administration and developed in cooperation with the trade associations, called Good Manufacturing Practices or GMP, will provide even more safeguards. Up until the passage of GMP, the FDA’s regulations were inadequate to enforce the proper preventive practices in canneries. The GMP regulations, passed on January 24, 1973, and since, contain at least four important preventive measures to insure the safety of commercially processed foods, according to the Extension food technologist.
Many safe products have been recalled, as in the recent “mushroom recall,” simply because can codes and plant records would not permit isolating the suspect cans to a few cases. According to Dr. Kuhn, FDA has new coding and record requirements which will aid in resolving this problem.. Dr. Kuhn re-emphasizes the creditable safety record maintained by commercial food processors in this country and says that the basic rule to knowing whether a canned food product is free from poisonous toxins is to keep in mind that the contents of unswelled cans are Baft to eat He offers these additional guidelines for judging food safety: — Look for leaks in containers. If you detect a leak, don’t buy that can. If the leaking can is already on your shelf, discard it. — When opening canned foods. check for unnatural odors. If an “off odor is present discard the can: do not taste the food before first boiling it for 10 minutes. Boiling will de-toxify the botulism toxin.7
A 1975 public workshop mention flags his specialty field as being fruits and vegetables:
The Pennsylvania State University Division of Food Science is offering a one-day workshop on Food Safety, to be held April 3, at the Holiday Inn in Monroeville. Four specialists will contribute to the discussion. Speakers and their fields: Dr. Gerald Kuhn — fruits and vegetables; Dr. Morris West — poultry and eggs; Dr. William Jones — meats; Sidney Barnard — dairy.” (( Food Handler Safety Aids To Be Given. Kittanning Simpson Leader Times. Kittanning, Pennsylvania. 20 February 1975. Page 6. Col 4.))
In 1975, there was a home canning lid shortage in North America. Manufacturers had been caught off guard by a resurgence in popularity of home canning. Kuhn was tapped in July of that year to give home canners some lid advice:
In less than two months frost will settle onto parts of the state and the gardening season will be almost over. Will Pennsylvania growers get their canning lids before it’s too late? No. — The two largest manufacturers of canning lids — the Kerr Glass Manufacturing Co. and the Ball Corp. — say they are operating at maximum output but will not meet the summer’s demands. The firms report they are producing lids 24 hours a day, seven days a week. Still, they predict no relief this year for Pennsylvania home canners. However, there are alternatives. ‘With nothing else, without lids, we have to turn to something.’ says Dr. Gerald Kuhn, associate professor of food sciences at Penn State University. Dr. Kuhn says paraffin wax seals — applied with care — can be used for canning jellies. But wrap the jar top with tin foil and seal it firmly around the glass with rubber bands. Wax is not recommended for canning fruits and vegetables. The old zinc lids, which cost more than modern sealers and are not as reliable, because they come in four separate pieces instead of the modern two-piece lids reportedly available in adequate supplies around the state. But Dr. Kuhn advises first-time, canners not to use these without seeking help from someone who has worked with zinc lids before. Dr. Kuhn says there are one-piece lids available that sometimes can be used in food canning. ‘Examine it closely,’ he says. ‘If a one-piece lid and the gasket are typical of what you see in a two-piece lid then this could be acceptable. We’re getting more and more of these one-piece lids into the state almost on a daily basis.’ Dr. Kuhn advises would-be canners to freeze the produce whenever possible. He also says that though frost means the end of this summer’s general gardening, some foods like carrots and apples can survive and be ‘put up’ well into autumn.”8
In August of that same year, he advised home canners to be cautious of new-style lids:
Only time and use will tell tell whether new-type canning lids will maintain the seal and shelf life of conventional two-piece, tin lids, say Penn State researchers. There are various plastic and one-piece metal canning lids on the market. The caution is given by Louise Hamilton, Penn State food and nutrition specialist, and Gerald Kuhn, a food technologist at the university. If homemakers opt to use the new lids during the conventional lid shortage, the Penn State researchers offer these suggestions: —Buy a small quantity until sure of effectiveness. The new lids cost more than the old variety…”9
By 1975, he began trying to warn people against old-style, unsound canning methods. He co-authored a book, “Home Canning, The Last Word.” (1975, Countryside Press, Philadelphia.)
Many first-time home canners may get off to a bad start if they are using methods found in grandma’s recipe book, caution food experts in several books. Grandma may have been a whiz at measurements, a pinch of this and a lump of that, but the leeway she took in home canning may not necessarily be safe. For that matter, even methods to be found in older cookbooks and some printed in the 70s may be in error. So say food and nutrition specialists Louise W. Hamilton, Gerald D. Kuhn and Karen Rugh in a book, “Home Canning, The Last Word,” they put together with editors of the Farm Journal. That trio emphasizes that open kettle canning by dishwasher — people do it — and canning with aspirin to change the acidity of food are unsafe practices. Then, too, some new jar lids that recently came on the market when lids were scarce do not “consistently seal or maintain a seal.” After considerable investigation, too, of the new tomato varieties and their relationship to a possible outbreak of botulism, it has been decided that home canned tomatoes spoil because heat sterilization time was too short, they say. Open kettle canning, a method that is particularly popular with jelly makers — the food is cooked in open kettles and packed boiling hot in sterilized jars and quickly sealed — is no longer recommended, not even for jams and preserves, they point out, explaining ‘the unsafe practice has resulted in food spoilage and even botulism.’ It has been established that heating food in open kettles will not destroy spoilage organisms. This knowledgeable group also does not encourage sealing jams and jellies with paraffin.10
Though Kuhn’s knowledge was evolving thanks to research, in 1976 he hadn’t yet arrived at home-canned tomatoes needing added acidity, as he would later in the 1980s:
The acidity of tomatoes is determined by the variety and growing conditions. I recently attended a canning in-service training meeting presented by the food technology specialists at Penn State. Dr. Gerald Kuhn, food technologist, reported that samples of tomatoes grown in Pennsylvania have been checked for acidity and are acid enough to allow normal canning using a boiling water bath method, providing that the tomatoes or juice are processed in jars long enough to destroy potentially dangerous bacteria….. We are NOT recommending the addition of lemon juice or citric acid or vinegar to increase acidity. Pennsylvania tomatoes are safe to can if you use proper methods.”11
In 1977, his job title was still being cited as Associate Professor of Food Technology.12
Intensive research period
In 1977, Kuhn released results of a canning lid study he had been undertaking:
Are you still troubled by canning lid failures and confused by different types of available lids? Food scientists at The Pennsylvania State University have found in canning lid research that: Forty-nine per cent of women surveyed were still experiencing canning failures in 1976. Many problems are caused by failure to tighten the lid enough. Of three types of lids tested, all performed well, including the first-ever aluminum lid on the market and a reusable lid made of traditional steel alloy. The study was a follow-up to the first and only impartial testing of canning lids ever done in the United States. Both studies were the work of Dr Gerald D. Kuhn, professor of food science extension , and Louise W. Hamilton, professor of food and nutrition extension. The first, done with state and national funds, attracted nationwide attention last year because it named which of nine canning lids were acceptable and which were not. In the wake of the report, the number of canning lid producers began to decline from the all-time peak of about 30 it had reached in 1976. Most of these companies had started manufacturing lids as a result of shortages caused by the sudden upsurge in home gardening and canning, beginning in 1974. The current study was commissioned by three lid manufacturers whose products had not been tested earlier. Professor Kuhn and Hamilton had complete control over testing procedures and results.
The study consisted of two parts. To begin, the researchers conducted a survey at a shopping center. They asked women who do frequent canning to tighten regular-size and widemouth lids on pint-sized Mason jars. They then used a “torquemeter”, a machine which measures the tightness of lid screw bands, to determine the range of tightness applied. From these studies, they selected three tightness levels to be used in evaluating jar lid performance. ‘We found in the survey,’ says Dr Kuhn, ‘with regular size lids, 28 per cent of the home canners used less than the lowest tightness, while eight per cent used more than the highest. With wide-mouth lids, 21 per cent used less than the minimum pressure, and 20 per cent used more than the maximum.’ The results were important because related torquemeter testing of some 3,000 canning lids showed jars sealed at the lowest tightness and had double the seal failure rate as those tightened with either medium or high pressure. ‘This means,’ says Hamilton, ‘many canners don’t tighten their jars enough, and this can lead to seal failures and spoilage.’
How tight the lid is on, as well as its quality and design, are crucial. The most common home canning technique involves packing the produce into a glass jar, sterilizing it with heat which allows air but not liquid to escape, and sealing it against re-entry of oxygen. In recent years most canners have used a two-piece self sealing lid. One piece consists of a flat metal surface with a rubberized sealer along one edge. This fits over the mouth of the jar. During the cooking or sterilization phase a screw band holds the lid in place. After cooking, the band is removed for cleaning and reuse. If a lid is sound, it will maintain the vacuum inside the jar, and prevent contamination by microorganisms which cause spoilage.
Some lids, say the researchers, malfunction due to defects in the lid itself or the sealer. However, sometimes the home canner, not the lid, is to blame, because the sealing surface wasn’t cleaned properly, the jar was overfilled, or both. Professors Kuhn and Hamilton tested 192 samples of each of three different lids.
Two were two-piece lids, BFG Home Canning Lids and Harvest Time, an aluminum lid. Also tested was Klik-lt, a one-piece reusable lid. Canning apples and carrots, the researchers found:
BFG lids — there were no failures due to lid defects nor was there rusting, and the lids “overall performance was excellent.” They recommended users tighten the screw band with average to high strength.
Harvest Time aluminum lid — there were no failures, no corrosion, and “overall performance was excellent,” even when screwed on with a low force. To avoid possible problems during storage when using aluminum lids with screw bands of another metal, they recommended the bands be removed after cooling.
Klik It (one-piece reusable lids) — there were no failures due to lid defects, even when lids were used five times. These one-piece lids were difficult to remove after storage. When screwed on with maximum pressure, lids buckled, but sealed during cooling.
With many good canning lids on the market, Kuhn and Hamilton say, there would be fewer canning failures if people examined lids before using them. ‘The things to look for are gaps in the gasket or sealer, or bumps, dents or anything unsmooth anywhere on the lid. After using a lid, if you find the gasket has slipped or torn, it’s best not to buy that brand again,’ stated the researchers. ‘Other lids to avoid’, stated Hamilton, ‘are those made of plastic, as well as traditional ones made of zinc or glass.’ All of these, Hamilton added, have shown high failure rate.”13
In 1977, he co-authored the USDA Yearbook of Agriculture:
USDA YEARBOOK OF AGRICULTURE: ‘Gardening for Food and Fun’ is a practical book for consumers who grow and preserve their own produce whether experienced or inexperienced. The 400-page, hard-bound volume includes a 32-page, color photo section depicting all stages of gardening, 56 chapters on subjects ranging from garden site selection, soils, tools and equipment, plant selection, culture, pest control, to specific information on growing fruits, vegetables and nuts. The fourth section includes the basics of food preservation — canning, freezing and drying foods.
Readers will find helpful charts on planting times, pest control programs, gardening spacing, produce yields, and two glossaries. In addition to the color photo section there are 171 black and white photos interspersed throughout the book. A chapter on ‘How to Minimize Quality Losses,’ included in the food preservation section of the book, was written by Louise W. Hamilton, professor of foods and nutrition Extension, and Gerald D. Kuhn, professor of food science Extension of the Cooperative Extension Service of The Pennsylvania State University.
Several of the photos in the new book have been supplied by Perm State College of Agriculture photographers. The 1977 Yearbook, ‘Gardening for Food and Fun’ is available from government bookstores of the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 for $16.50. Order by stock number 001-000-03679-3. In addition to the copies on sale, each member of Congress has available a limited supply of books available free to their constituents who write their representatives or senators requesting a copy.”14
Part of the advances Kuhn made required him to undertake more advanced theoretical research, even if it ended up with information that wouldn’t be applied directly in advice to consumers. In 1978, he reported results on preserving Vitamin C in home-canned fruits:
UNIVERSITY PARK — If you’re concerned about preserving nutrients in home canned apples, don’t worry about storing them in a dark, cool place. Just pack them raw, leave a big head space and use a pressure canner.
So say Pennsylvania State University researchers who, contrary to recommended home canning practices, have found that excessive light, temperature and air space do not affect vitamin C retention in home canned apples.
Dr. Gerald D. Kuhn and graduate student Mary A. Keith also found that the recommended combination of hot pack and boiling water canning is not as good, nutrient-wise, as canning apples raw with a pressure system, using a process schedule of eight minutes at 10 pounds of pressure.
Essentially, the researchers discovered that the best way to preserve vitamin C in apples, is to pack them raw and leave a two-inch air space at the top before pressure canning. This method results, they say, in 40 to 60 percent more vitamin C than if the apples were packed hot with only one-quarter inch headspace, and canned with the boiling water method.
‘ We’re surprised by our results,’ says Dr. Kuhn a professor of food science. ‘We’ve long recommended that acid canned foods be cooked first, that jars be filled leaving little air space, that canning be done with boiling water, and that the jars then be stored in the dark at less than 70 degrees Fahrenheit. We’ve believed such methods would both prevent spoilage and lead to the best nutrient retention.’
Although their research is continuing, Miss Keith adds, ‘We believe our results with light intensity and storage temperature will be about the same, no matter how long the canned food sits on the shelf, and no matter what fruit or vegetable we use.’ Miss Keith, who’s working towards a masters in food science, presented the research results in Dallas, Tex. in June, at the Institute of Food Technologists’ national convention. She noted that apples were chosen for the research because of the large volume canned by the Pennsylvania housewife; and because, although they are not a high source of vitamin C for the human diet, their vitamin C nutrient is particularly sensitive to light, air, acidity and heat. After canning the apples in pint-sized jars with two-piece aluminum lids, using varying canning procedures and headspaces, the jars were stored at 55 or 88 degrees Fahrenheit, under fluorescent lights or in the dark. Some were opened about two, four, six, 12 and 24 weeks, while others still remain closed for future testing. Specifically, the researchers found that:
- Home canned apples stored under bright light and or at high temperature did not result in significantly greater loss of vitamin C than those stored in cool, dark areas;
- Regardless of whether apples are processed in boiling water or a pressure canner, between 10 and 20 percent more vitamin C is retained if the food is packed raw rather than cooked;
- Although pressure canning takes longer and is more expensive than boiling water canning (if you don’t have a pressure canner) it results in between 10 and 15 percent more vitamin C retention in canned apples; and
- Vitamin C retention was unaffected by the amount of head space when boiling water canning was done.
When the pressure canning method was used, however, and apples were packed raw, a two-inch headspace resulted in about 15 percent higher vitamin C. Noting that they concentrated only on nutrient retention, Dr. Kuhn says that certain tradeoffs might have to be considered if canners were interested in other food characteristics. For example, he says , when pressure canning is used, tomatoes and peaches soften. On the other hand, he concludes, pressure canning will not harm the flavor of foods, and in fact may enhance it.”
In 1978, he was drawn on for advice about apple sauce, in an era when the rule about processing all jars no exceptions hadn’t yet been hammered home. Note that at the end he says that if you process your jars, you won’t need to worry:
UNIVERSITY PARK – Apples of questionable quality, which result in spoiled home-canned applesauce, have been reported in some areas of Pennsylvania. ‘ Preserving top quality foods, whether canning or freezing, can’t be stressed enough,’ says Gerald D Kuhn, professor of food science Extension at Penn State University. In the case of apples having visible evidence of spotty mold growth, it is indeed possible that canned applesauce made from apples in the traditional manner may become moldy in jars, even when sealed. It is not necessary to be concerned about the mold problem if the applesauce is to be frozen because freezing arrests the mold growth, explains Kuhn. The recent problem with moldy home-canned applesauce involved washed but unpeeled apples cooked and made into sauce. Washing, points out Kuhn, will not remove mold spores. Apples having spotty mold lesions are not uncommon. However, the problem this fall may have been increased in some areas of Pennsylvania by weather or specific environmental conditions in the growing areas. Improper spray schedules or unattended backyard apple trees may be especially susceptible to disease or mold problems.
The Penn State professor says that applesauce made from apples of questionable quality can still be canned at home and will result in a safe food product. He recommends either of the following two methods: — Wash and peel apples before cooking to make applesauce. Peeling is not generally necessary when using quality apples. Heat process in boiling water canner 15 minutes for pints, 20 minutes for quarts — Wash apples and make sauce without peeling. Process in a pressure canner 10 minutes at 10 pounds of pressure for either pints or quarts.”15
In 1979, his labs finished a study on what the most energy efficient way of home preserving food is. The results showed that the most energy-efficient way of preserving food was canning in quart (litre) jars:
Energy-saving methods used for preservation of foods. UNIVERSITY PARK If you want to save money and energy while preserving fresh fruits and vegetables, don’t dry or freeze them – can them. So say Pennsylvania State University food scientists who found that, for sweet corn and peaches canning is, by far, the most economical energy saving method and oven drying the most expensive. Also oven drying though far faster, is up to seven times more costly than using specially designed home driers. In the nation’s first reported energy cost comparison of home preserving methods, Dr Gerald D Kuhn, professor of food science, and his student Mary A Keith and Catherine E Adams, also learned that:
- Drying is two to 13 times more expensive than canning, and may result in brown, burnt tasting food, particularly if done in the oven.
- Freezing costs between five and six times more than canning.
- For many acid foods including cherries and peaches, raw versus hot pack canning does not save energy because it takes longer to process raw packed jars.
- Canning in quarts rather than in pints requires 18 percent less energy.
‘We tested peaches and corn,’ says Dr Kuhn, ‘because they are popular products for both home drying and canning, and because the costs of preserving other fruits and vegetables would be comparable.’
In recent years, more and more people have been preserving home grown fruits and vegetables or those bought from farm and produce markets. In 1975, Cornell University researchers estimated the cost of home freezing, but until now, there were no comparative estimates for drying and canning. To obtain such comparisons. Dr Kuhn’s group measured the energy cost per edible pound of corn and peaches, in a home paying four cents per kilowatt hour of electricity. First they built two drying apparatus: a simple convection drier, which costs $30 to construct, is powered by four 60 watt light bulbs has two drying racks and maintains a temperature of between 120 and 130 degrees Fahrenheit, and a forced air drier, which costs $75, uses nine 60 watt bulbs, has a small fan, a thermostat and five drying racks, and operates at about 124 degrees.
In each device, the corn kernels were dried until brittle and the peach slices until leathery. In an electric oven, peaches and com were dried on oven racks covered with tightly stretched cheesecloth. In a generally unsuccessful attempt to keep the temperature from exceeding 120 degrees the oven was turned to its lowest setting, the door was left slightly open and an electric fan blew air past the door. The two foods also were canned, by both standard methods in pint and quart sized Mason jars.
‘We found,’ says Dr Kuhn ‘that the greatest energy cost differences were between drying in the oven and canning or drying in bulb-powered driers. Comparing our results on drying and canning to Cornell’s on freezing, we saw enormous variations. We determined that, in 1979, the preserving costs per pound were:
- Peaches 2.7 cents by forced air drying, 3 9 cents by convection drying, 19 cents in the oven, and about 9.8 cents in the freezer. Both raw and hot pack peaches cost 1.6 cents to can in pints, but only 1.4 cents in quarts.
- Corn kernels 2.5 and 3.6 cents, respectively, for forced air and convection, 11.5 cents in the oven and about 9.8 cents in the freezer. In pints, the respective hot and raw pack cost were 2 and 1.7 cents.
‘In conclusion,’ says Dr Kuhn, ‘canning was by far the cheapest method from an energy standpoint. Although oven drying takes about half the time of homebuilt driers, it’s far more costly, and often results in excessively browned food. As for the two home driers although the forced air model cost much more to build, it is more economical and easier to operate.'”16
In 1979, he reminded people that jars of home-canned tomatoes needed to be processed. Notice, though, that he had not yet made the journey to recommending acidification:
‘Open Kettle’ Canning Risky For Tomatoes ‘ UNIVERSITY PARK,. (UPI) — Backyard gardeners who want to store their juicy crop of tomatoes for use this winter should refrain from using the “open kettle” method of canning, says a food expert at the Pennsylvania State University. Dr. Gerald D. Kuhn, a professor of food science, said the method poses spoilage dangers when acidic foods are locked inside the jars. He suggests use of another canning method, the “boiling water” process, for tomatoes and tomato juice. Food experts have been aware of the hazards for acidic foods for some time, but Kuhn, along with a university research team, is the first to document the problem. The group presented their findings recently at the Institute of Food Technologists’ annual convention in St Louis, Mo.
“We’ve demonstrated beyond a reasonable doubt,” Kuhn says, “that for tomatoes this method can’t guarantee 100 percent safety. The spoilage rate can climb dramatically to over 50 percent when a hurried home canner tries either to cut corners or combine open kettle and boiling water processing methods.” The “open kettle method” calls for boiling the juice for 15 minutes after pressing the tomatoes; boiling the jars and lids for 15 minutes; filling the jars with boiling juice; sealing them; and allowing the jars to cool upside-down. But Kuhn says this method isn’t foolproof. “Unfortunately,” says Kuhn, “many home canners often shorten the boiling-time, allow the juice to cool before filling, or neglect to invert the jars. The “boiling water” method is safe when done correctly, Kuhn says, and even if part of the procedure is poorly done, it’s still far ‘more safe than “open kettle” canning under the best conditions. The “boiling water” method begins with a clean and preferably hot jar that is filled with either raw or hot cooked food. The lid is closed tightly and the jar is put in boiling water for a specified time, depending upon the food.”17
In 1981, he was called upon to quell an odd controversy, as to whether a variety of tomato called “Manalucie” could be home-canned or not:
Manalucie Tomatoes May Be Canned. “Yes, you may safely can Manalucie tomatoes,” says Gerald D. Kuhn, professor of food science Extension at Penn State. At least one supplier’s seed packet warns the consumer not to can this tomato variety. “Research shows no reason for this,” Dr Kuhn says. “In fact, the U.S. Department of Agriculture has included Manalucie tomatoes on its list of tomatoes suitable for canning. “Can only high-quality tomatoes and be sure they are washed and trimmed. Use the hot pack method of filling the jars,” he recommends, “ and pack the tomatoes quickly to avoid cool-down.’’ Process in a boiling water canner and refer to modern canning instructions for timing.”18
His advice was sought on more than just home canning, however. In 1981, he advised on “microwave blanching”, which was being talked about:
A newer method gaining attention is microwave blanching. Some cookbooks that come with microwave ovens recommend this. Its biggest appeal is that it doesn’t steam up the kitchen on hot days. But according to Dr. Gerald Kuhn, professor of food science Extension at The Pennsylvania State University, the times these cookbooks recommend are very inadequate. Kuhn’s preliminary research indicates that the recommended times would have to be increased two to three times for proper blanching. He strongly recommends sticking with water or steam blanching until research can document complete blanching recommendations for microwave ovens.”19
In 1981, he advised against stocking up on canning lids too far in advance:
STATE COLLEGE ( A P ) — A Penn State expert says using last year’s lids on this year’s canning could be a mistake. Gerald Kuhn, professor of food science, says dried out gaskets won’t give a proper seal. Most lid gaskets have a rough-textured rubber seal which, if stored in a cool, dry place, will last up to three years. But lids with a smooth latex rubber seal tend to dry out faster and should not be kept more than one year, he says. The trouble is, it’s hard to know how old a lid is when you buy it. However, some makers are starting to date their lids. “For best results this year, discard any lids you have from years past, especially if you have stored them in the kitchen or some other warm place. Start over with new lids, preferably dated ones. If you do save leftover lids, store them in a cool, dry place.” he said.”20
In the fall of 1981, he got dragged into a trend that was sweeping the nation; he and his team found themselves having to develop a safe version of Zucchini Pineapple.
In the summer of 1982, Penn State released a publication titled “How to Freeze Food the right way”, authored by Kuhn and Anna V.A. Resurrecion.21
In the fall of 1982, Kuhn warned of a manufacturing flaw in Bernardin canning lids that year:
Canning Jar Lids May Harm Food UNIVERSITY PARK, Pa. (UPI) – A Pennsylvania State University professor says a modification in a brand of canning jar lids could affect the safety of home canned products. Dr. Gerald D. Kuhn, professor of Penn State, said Thursday the problem lids are the 1982 Bernardin canning jar lids marketed through the Weis supermarket chain in Pennsylvania. Kuhn said consumers can return unused jar lids directly to Weis or to Tom May, Bernardin Inc., P.O. Box 725, Evansville, Ind., 47705, for a full refund. The minor modification requires that the lids must be perfectly centered to insure a proper seal. “This is too restrictive for consumers,” he said. “If the lid is slightly off center, there’s a potential for the metal skirt of the lid to interfere with the necessary compression.”22
In the fall of 1982, the Chicago Tylenol murders occurred when someone tampered with the packaging (the villain was never found.) Kuhn was called upon to discuss food packaging safety:
Penn State Scientists Discuss Food Packaging UNIVERSITY PARK – The nation’s food manufacturers can increase their sales and prevent another Tylenol- type tragedy by expanding the use of certain packaging safeguards, two Penn State scientists say. Drs. Manfred Kroger and Gerald Kuhn, professors of food science, suggest food makers make greater use of “shrink wraps” and paper seals to prevent tampering. A shrink wrap is a heat-shrunk plastic band that must be unwrapped to open the lids of some products. Paper seals, now seen on liquor bottles, must be torn to unscrew bottle caps or as with coffee jars, broken after unscrewing the cap. “You can’t tamper-proof every product, but that doesn’t mean we shouldn’t make an effort,” Dr. Kuhn said. “Shrink wraps and paper seals are steps in the right direction.” What’s worrisome, the scientists point out, is that much of the food industry is using packaging vulnerable to tampering. “I feel certain the vulnerable products are being addressed in board meetings right now,” Dr. Kroger said. “I think most officials will analyze the possibility of using tamper-proof devices. If it’s reasonable, affordable and if the technology is there, it will be done.”
The problem with the lids and caps on many food items is that their removal or unwrapping does not signal to potential consumers possible tampering or contamination, the scientists said. Of particular concern to them are bottled goods that have twist caps, such as sodas, some spices and vinegar. These need better protection, the Penn State professors believe, as do many snacks and fresh and frozen foods. Hermetically sealed or airtight- sealed products, which include all canned goods, are the best protected, Dr. Kuhns and Kroger note. Cereals and some lunch meats also fit into this category. “Any manufacturer that produces a tamper resistant product would immediately enjoy increased sales,” Dr. Kuhn says. “Consumers are anxious to buy a safe product.”
One problem with tamper-proof devices, he believes, is a shortage of equipment for making these kinds of sealants. It could take as much as a year to tamper-proof many products, he said. The doctors note that the food industry tries to protect its products from three things: oxidation, which causes staleness and loss of flavor; moisture loss, which causes weight loss in foods such as cheese, and filth, which makes it possible for toxic or spoilage microorganisms to enter food. The food industry has, in fact, taken precautions against tampering. “I don’t mean tampering in the sense of adding a poison or anything like that,” Dr. Kuhn said. “But a number of manufacturers took steps as long as 10 years ago to prevent people from smelling and touching products.” Manufacturers of baby food, for example, created a vacuum-filled jar. Because of the vacuum, the lids on baby jars are concave. When a jar is opened, the lid flattens out, a signal to the potential buyer that something is wrong.
Dr. Kroger believes the decision to offer tamper proof containers hinges on cost more than anything else, because the consumer would have to pay the bill. “If a $1 product is going to cost 30, 40 or 50 cents more, it would not be worth it,” he said. “Food protection by packaging is expensive as it is. Some food packages, like beer cans, now cost more than the food they contain.”23
In the fall of 1983, Kuhn was called on to examine the safety of another trending recipe, this time for ‘Blender Ketchup’:
Have you canned all the tomatoes you think your family will use next year? Are you looking for easy ways to preserve the tomatoes you have left? A recipe for catsup using fresh tomatoes and a blender has surfaced recently. Although the recipe is a quick way to make catsup, it could be unsafe and it’s not very nutritious according to Dr. Gerald D. Kuhn, professor of food-science Extension at Penn State. The recipe directs you to chop up tomatoes in a blender, then let the mixture set at room temperature for eight hours while the juice separates from the more solid part of the mixture. This mixture is susceptible to bacterial growth during this time and may result in more bacteria than can be killed during processing later. This is what makes the recipe unsafe. Because most of the nutrients are in the juices that you strain off, the catsup is not as nutritious as catsup made from standard recipes. Even adding the sugar and spices that the recipe calls for won’t replace the nutrients or the taste lost in the process. ”24
The USDA Complete Guide Project
In 1984, the announcement was made that Penn State’s Food Science Department had been successful in its project proposal to champion a thorough overhaul of the USDA’s canning recommendations.
UNIVERSITY PARK — Penn State’s Food Science Department has been awarded a five-year grant for a home food preservation center of excellence, extension food scientist Gerald D. Kuhn announced. The grant — $60,000 the first year and more than $100,000 over each of the next four years — will be jointly funded by the USDA’s Extension Service, Cooperative State Research Service and Agricultural Research Service. Kuhn said the grant is timely because food preservation projects are now popular in American kitchens.”25
A February 1985 article sheds more light on the scope of the project.
UNIVERSITY PARK – Home canning done correctly can remind us in the middle of winter of the sweet taste of our garden harvests. Done incorrectly, a hostess could be serving up a trip to the hospital when she puts last fall’s spaghetti sauce on her table. Illness stemming from eating home canned food is unnecessary, and researchers at Pennsylvania State University — considered the leading authorities in the field of understanding home preservation — are striving to do away with the outdated and unsafe methods of food storage and preservation that cause it. Because of its recognized leadership, the University’s Food Science Department has been awarded a five-year grant to establish the first Home Food Preservation Center of Excellence in the United States.
Funding to operate the center totals $60,000 for the first year, and more than $100,000 in each of the next four years. It was jointly offered by the U.S. Department of Agriculture’s Extension Service, Cooperative State Research Service and Agricultural Research Service.
“It is an awesome responsibility in terms of the services we will be asked to perform.” says Gerald D. Kuhn, professor of food science and project leader. “We will have this become the national base of information for our peers, and for consumers, through the extension service.” Kuhn says Penn State began studying home preservation techniques in the mid-1970s, when home canning regained popularity after it was lost as a family art in the 1950s. ‘Valuable publications on the matter ceased in the ‘50s,’ he says. Interest died off until 1975, when the energy crisis took hold and gardening became popular again. Gardeners renewed interest in preserving their harvests. However, the methods the preservers were using were suspect. ‘Anything is safe — put it in a jar and put a lid on it.” Kuhn explains is the concept many preservers were using. This naturally led to outbreaks of bacterial problems and increased cases of botulism. ‘We still have outbreaks of botulism,’ he says. ‘Many changes have occurred during the last 20 years in terms of horticultural varieties, canning ingredients, equipment, home kitchens, lifestyles and preferences for foods.’ Kuhn says. That is what the Penn State Center of Excellence team will be studying. Working with Kuhn are Dr. Sudhir Sastry, assistant professor of food engineering; Dr. Stephanie Doores, assistant professor of food science; Elizabeth Andress, research assistant; and Thomas Dimick, senior research technician.
The team currently is working on venting practices and how they alter heat penetration, as well as a jar lid evaluation. In the summer, as the center is moved into its own facility and receives its computerized data acquisition system, the team will study several priority issues in the field, Kuhn says. The team will review equipment, including dial and weighted pressure gauges, and the use of pressure cookers, as well as the re-evaluation and establishment of processes for various foods which need new data bases. Kuhn says. The foods cover a wide range, and include asparagus, spinach, corn, peas, ground meat, heart, tongue, soup stock, rabbit, all forms of tomato products and combination products. Miscellaneous projects will include special diet requirement foods, pie fillings and seafoods, such as salmon and tuna, Kuhn says.
Future work may focus on new equipment, such as microprocessor-controlled canning. For now the center is focusing on canning, but may expand to study freezing, drying and pickling techniques.
Andress, who with Kuhn organized a graduate-level seminar for extension personnel held at The Louisiana State University last year, says that each state issues pamphlets defining safe canning procedures, and ‘there is a lot of variety among them. A center can alleviate that problem.’ Dr. Sastry adds that the center can become a source of data for the industry and the consumer. ‘We should be influencing all recommendations being made by the U S. Department of Agriculture,’ he says. Kuhn says the equipment companies are looking to Penn State as a source of unbiased information. ‘Our name may not be on it, but it is likely that it began here,’ he says of new advances in equipment for home canners. The team recognizes that one of its hardest tasks may well be convincing people that what they learned at ‘grandmother’s knee’ may not be the safest method to use. ‘We still have many doubters but we hope that will continue to change,’ he said.”26
In 1985, Kuhn’s Penn State team developed the famous Clearjel pie filling recipes still used by home canners today:
Often homemakers like to make use of summer’s fruit goodness in different ways. Have you thought about canning it as a pie filing for winter use?. Most of the pie fillings that are available come in cans at the grocery store, but research has been conducted by Dr. Gerald Kuhn for making your own pie filling. This can be frozen or canned for later use. In working with this problem, the key ingredient to success was to use the right thickener Corn starch will set to an opaque gel when cool. But it will break down when exposed to the high temperature needed to process as a canned product, when thawed after freezing, or when used with a high acid fruit. Flour, if it’s used as a thickener, will not give a clear stable product either. One can use the instant type granular tapioca in canned pie filling but it tends to separate and be clumpy.
So what is the answer if you would like to have canned pie filling for next winter? It is to use a product called Clearjel (R ). This is a suggestion that food technologists from the food science lab at Penn State have recommended. This product is manufactured by the National Starch and Chemical Corporation for the food processing industry. It is available in 100 pound bags and may be purchased in bulk. It may be found locally from bulk food repackers for sale in one pound bags. Dr. Kuhn has cautioned the consumer that not all products sold as Clearjel ( R ) are the specific product. You may need to ask questions before you buy this thickener. Instant Clearjel (R) is a different product. This is intended to be used with cold liquids only and cannot be frozen or canned. Clearjel ( R ) can be used also for fresh pie fillings, to thicken cream soups, stews, gravies and sauces. Use it in the same proportion as cornstarch, one tablespoon per one cup (or two) liquid, depending upon how thick you want it.”27
In August 1987, Kuhn was made a fellow by the Institute of Food Technologists.28
A later article in 1987 article projected a January 1988 release date for the new Complete Guide to Home Canning:
UNIVERSITY PARK, Pa. (AP) – Grandma’s canned pickles or tomatoes may not have sickened or killed anyone, but that does not prove her food preservation methods were safe, according to a Penn State researcher. ‘In response to a massive return to home gardening and home canning in the mid-1970s (during the energy crisis) we began a systematic investigation of proper and safe methods for preserving fresh produce,’ Dr. Gerald Kuhn, professor of food science, said. Today, as many as 65 million Americans are eating home-canned food, and more than 100 million are eating home-frozen food, he noted.
With funding from the U.S. Department of Agriculture, Kuhn and his research technician, Tom Dimick, began a scientific study of home canning and freezing methods. The USDA has designated Penn State a Center of Excellence in Food Preservation, the only such center in the nation. Kuhn serves as the center’s director. “ Our goal is to back up each food preservation recommendation with scientific research.” Kuhn said. “ We want to help people preserve higher quality food that has better color, cleaner flavor, longer shelf life and more nutrients than previous canning and freezing methods were capable of producing. ‘We also want to re-educate people about safe preservation methods.’ he added. ‘Renewed interest in canning and freezing in 1975 resulted in a high incidence of botulism, which was traced to home canning methods.’ Clostridium botulinum, a spore forming bacteria, grows in foods nearly depleted of oxygen. When conditions favorable for growth occur, the cells multiply and produce a deadly toxin.
To take the risk out of food preservation, Kuhn and Dimick, a graduate student, reviewed existing canning and freezing publications and are lab-testing the directions. They will make their research results available to the USDA and draft two new, comprehensive publications on canning and freezing. The USDA plans to release the publications, which will become the national standards, Kuhn noted. The first publication, on canning, will be printed in January. The second. covering freezing methods, will be available in 1989, he said. The new standards will cover step-by-step directions for obtaining food, either by growing it or buying it in bulk; canning and freezing it; and preparing it for consumption. In addition to the comprehensive canning and freezing guides, Kuhn has started a supplemental series called ‘Let’s Preserve’ which addresses, in brief form, preservation methods for foods not commonly grown in the home garden. Already available are ‘Let’s Preserve’ directions for preserving cherries, apricots, nectarines, peaches, strawberries and other berries, pears, snap beans, sweet corn and leafy greens. It will also provide instructions for making sauerkraut and fruit pie fillings.”29
In 1988, he helped bring the Master Food Preserver program to Pennsylvania.
In August 1988, the crowning achievement of the big project was released: the USDA Complete Guide to Home Canning.
UNIVERSITY PARK – One hundred and seventy years of canning research and experience have been compiled, distilled and preserved in the USDA’s new ‘Complete Guide to Home Canning.’ The guide will help home canners reduce the risk of seal failure and spoilage, improving the quality of home-canned food. The 150-page color publication provides contemporary science-based home canning recommendations and more complete information than the four earlier USDA Home and Garden Bulletins it replaces. ‘Principles of Home Canning’, the book’s opening guide, examines safe canning practices and the best methods to preserve quality. It includes tips on ensuring safety, testing jar seals, storing canned foods and identifying and handling spoiled canned food. The book has six other guides that explain how to can specific types of foods such as fruits, tomatoes, vegetables, meats, fermented foods, jams and jellies. Recipes and ideas for making new products are included as well.
Penn State professor of food science Gerald Kuhn, Elizabeth Andress, and Thomas Dimick, a Penn State research aide, wrote and directed publication of the book for the USDA. Several national USDA Cooperative Extension staff members provided illustrations and information for the guide. Pennsylvania has purchased a limited number of books from USDA. They are available at a reduced price of $6 through the mail from the College of Agriculture’s Mail Room, 112 Agricultural Administration Building, University Park, Pa. 16802. Additional copies are available through the government Printing Office at the standard price of $11.30
Life after the USDA Complete Guide project
Some people have attributed a home-canned cake recipe to him, but we have not been able to locate any backup for that from reputable sources.
In 1994, Kuhn retired from Penn State, but acted as an instructor for the Better Processing School at Penn State.31
In the same year, he also authored a thirteen-page pamphlet titled ‘Making, Handling and Marketing Safe, High-quality Apple Cider’. It was published by PennState, College of Agricultural Sciences, Cooperative Extension.
In 2008, he provided some expertise for the book “Chester County Mushroom Farming.”32
Kuhn died, aged 80, on 28 April 2011 in Sebring, Florida.
Note: We have seen photos of Dr Kuhn out there on the Internet, but have reproduced none of them here as none have been released for re-use.
Their children were Jeffrey, Jill, Gerald, and Patricia. ↩
“In October of 1967, Dr. Gerald D. Kuhn became associate professor of Food Technology Extension at Penn State.” Snetsinger, Robert. Mushrooms and Penn State: Past, Present, Future. Bulletin 767, May 1970. Penn State University Agricultural Experiment Station, University Park, Pennsylvania. Page 24. ↩
Ag Extension. In: Gettysburg Times. Gettysburg, Pennsylvania. 11 December 1968. Page 3, col. 4 ↩
Don Horst Among Speakers For Symposium On How To Raise, Sell Golden Delicious. In: Gettysburg Times. Gettysburg, Pennsylvania. 13 July 1970. Page 9, col. 1 ↩
Extension Agent’s Notebook. Somerset Daily American. 26 October 1971. Page 8. Col. 8. ↩
Penn State ‘Home and Garden’ Shows to focus on Food Safety, Illnesses. Kittanning Simpson Leader Times. Kittanning, Pennsylvania. 21 July 1973. Page 24. Col 4. ↩
New Canning Rules Help Avoid Mishaps. Gettysburg Times. Gettysburg, Pennsylvania. 23 February 1974. Page 19, Col. 1. ↩
What You can do. The Evening Standard. 24 July 1975. Page 1. Col. 4. ↩
Time, Use needed for new lids. The Progress. Clearfield, Pennsylvania. 12 August 1975. Page 2, col. 1. ↩
Brown, Vivian. Experts warn against unsafe canning. In: Delaware County Daily Times. Chester, Pennsylvania. 10 August 1975. Page 20. Col. 1. ↩
Schadler, Alletta (Lebanon County Extension Agent). Low Acid Tomatoes? Farm and Home Column. Lebanon Daily News. Lebanon, Pennsylvania. 15 May 1976. page 15, col. 4. ↩
Honesdale Wayne Independent. Thursday, February 24, 1977, Honesdale, Pennsylvania. Page 6, Col. 6. ↩
Canning? Read ‘Test’ Results. Warren Times Observer. Warren, Pennsylvania. 2 August 1977. Page 7. Col 3. ↩
USDA Yearbook of Agriculture. Lebanon Daily News. Lebanon, Pennsylvania. 16 November 1977. Page 42, col 2. ↩
Beware Spoiled Apples. Hanover Evening Sun. Hanover, Pennsylvania. 18 October 1978. Page A-7. Col. 5. ↩
The News-Herald. Franklin and Oil City, Pennsylvania. 10 August 1979. Page 4. Col. 2. ↩
Open Kettle Canning Risky for Tomatoes. Tyrone Daily Herald. Tyrone, Pennsylvania. 24 September 1979. Page 8. Col. 6. ↩
Manalulcie Tomatoes May Be Canned. Greenville Record Argus. Greenville, Pennsylvania. 18 July 1981. Page 5, col. 8. ↩
Blanching Vegeys for Freezing Is A Must. Tyrone Daily Herald. Tyrone, Pennsylvania. 29 July 1981. Page 3. Col. 3. ↩
Indiana Evening Gazette. Indiana, Pennsylvania. 9 September 1981. Page 37. Col. 5. ↩
New freezing guide. Monessen Valley Independent. Monessen, Pennsylvania. 28 June 1982. Page 6. Col. 6. ↩
Canning Jar Lids May Harm Food. Clearfield Progress. Clearfield, Pennsylvania. 10 September 1982. Page 6. Col. 6. ↩
Penn State Scientists Discuss Food Packaging. Clearfield Progress. Clearfield, Pennsylvania. 28 October 1982. Page 9. Col. 2. ↩
Boran, Karen. Bad News About Blender Catsup. Huntingdon Daily News. Huntingdon, Pennsylvania. 1 September 1983. Page 9. Col. 7. ↩
News from Around Here. Tyrone Daily Herald. Tyrone, Pennsylvania. 22 December 1984. Page 7. Col. 3. ↩
PSU center plans study of canning. Altoona Mirror. Altoona, Pennsylvania. 27 February 1985. Page D11. Col. 2. ↩
Garris, Eleanor L. Home-canned pie filling will carry summer to winter. Gettysburg Times. Gettysburg, Pennsylvania. 4 September 1985. Page 6. Col. 1. ↩
“Dr. Gerald Kuhn, professor of food science, has been named a fellow by the Institute of Food Technologists. IFT is a professional scientific society of 23,000 food scientists and technologists.” Penn State Intercom. https://archive.org/details/pennstateintercov1718univ . August 27, 1987 Volume 17, Number 1. ↩
Penn State University offers free home canning and freezing guide. Greenville Record Argus. Greenville, Pennsylvania. 23 September 1987. Page 5. Col. 3. ↩
Preserving Guide is Updated. Altoona Mirror. Altoona, Pennsylvania. 2 August 1989. Page 32. Col. 1. ↩
School Focuses on safe food processing at PSU. Tyrone Daily Herald. Tyrone, Pennsylvania. 11 February 1994. Page 7, Col. 3. ↩
Bruce Edward Mowday. Arcadia Publishing, Jul 7, 2008 ↩