Home canning is very small scale in the UK. People might do a few small pots of jam, or a few pickled things such as pickled onions. But it is not practised on the same scale, depth and breadth-wise, as is encountered in North America. For one, people don’t have the storage space. Homes are smaller, and basements are rare. Consequently, even bulk food stores are rare (though you may see a grocery store offering a bin or two of bulk candy from time to time.)
Home preserving in jars in the UK is usually called just “bottling”, because that’s all it is: just placing food in a bottle — there is no subsequent canning process.
If you are set in your ways and have no intention of learning about the newer, safer way to do it, then you might just as well skip this page unless you get frissons of joy from being outraged.
But, and here’s the kicker: the new, safer way of “bottling” actually gives you a better quality food product, is less work and uses less cooking fuel. Click here if you just want that summary.
- 1 How did current practice in the UK come about?
- 2 Change in practice will be slow
- 3 4. Opinion trumping fact
Some typical questions that British home canners ask
- 4.1 1. What is processing a jar and does that apply to me in the UK?
- 4.2 2. Why is sticking food in a bottle and just whacking a lid on unsafe?
- 4.3 3. Surely all the sugar is enough of a preservative?
- 4.4 4. What is the danger?
- 4.5 5. Many people get “24-hour flu” and never realize it’s from a simple bottle of homemade jam
- 4.6 6. I’m okay with taking any “apparent” risk
- 5 The kicker: doing your home canning safely is actually less work
- 6 Further reading
How did current practice in the UK come about?
Sterilizing everything all together in the sealed jars saves time, money, energy, worry, and guarantees safety, and improves quality. There’s just no downside here.
During the Second World War, it was American and Canadian home economists who were sent over with much-needed equipment and supplies to cross-train Brits in what was felt to be the best practices of the time for home preserving — practices which are now 80 years old and long since discredited and documented as unsafe and unreliable back in North America. After the war, the practice largely died out in the UK, aside from the odd hobby jam made here and there, and allotmenteers who kept the practice alive here and there.
Whatever home bottling / canning advice there is in the UK now comes from private sources, such as cookbook writers, and TV and radio cooking problems, and the voluntary organization called the Women’s Institute (WI.) There is no government funding or official government studies done into best practices for home canning — perhaps because the practice is for all intents and purposes just an occasional hobby in the UK.
Sterilizing everything all together in the sealed jars saves time, money, energy, worry, guarantees safety, and improves quality. There’s no downside here.
Consequently, the UK sources still base their advice on long-term practice in the country ( a large part of which was reinforced by that ancient Second World War home economics body of knowledge), rather than basing it on modern research-based facts and testing. Just as advancements have been made in dentistry and health since World War Two, advancements have been made in the science of safe food preservation. Many things that people are still being advised to do — such as using sealing wax on jars — would have North American health professionals shaking their heads in disbelief.
The main food bottling technique followed in the UK is the long-discredited one of “open kettle canning”. That is the practice of just putting foods in jars, sticking a lid on and waiting for a seal, with no further processing of the jar done.
When the contents of the jar is a high-acid item such as a fruit jam, many old-time canners would say that the product you are going to get is probably going to be or at least seem okay for a while anyway. But certified, trained professionals in the field today warn that that’s not so.
Heat processing of all filled jars of home canned foods is not optional! It is essential to create an adequate hermetic or vacuum seal required for food safety as well as delicious taste and quality. All jars of home canned foods must be heat processed by the appropriate method for the correct time for the food type and jar size. Failure to adequately heat process jars can result in seal failure, food spoilage and substantial health risks.”  Bernardin Guide to Home Preserving. Toronto, Canada: Bernardin Ltd. 2013, page 4
Dr Elizabeth Andress, PhD, head of the National Center for Home Food Preservation, warns:
An old out-dated method of canning — the open-kettle method — is now considered unsafe….. . This method results in a very real danger of botulism with low-acid foods or acid foods that experience mould growth.”  Andress, Elizabeth L. and Judy A. Harrison. So Easy to Preserve. University of Georgia Cooperative Extension. Bulletin 989. Sixth Edition. 2014. Page 18
In an episode from BBC’s 1993 series “Wartime Garden and Kitchen”, Ruth Mott demonstrated the old old method of just “bottling” tomatoes, with no canning process occurring to sterilize the bottles and contents together. When asked how long the tomatoes would keep like that, Ruth answers, “We just have to watch them, really, more than anything.” In another episode, she admits there actually was a lot of spoilage. Wartime Garden and Kitchen, BBC. With Harry Dodson, Ruth Mott, et al. Episode 6. 1993. Start time: 16:23.
Change in practice will be slow
Change in British practice will likely be very slow to come owing to several factors.
1. The nationalistic factor
A great deal of national pride enters the argument. You will see dismissive statements such as, “I am British, and have made jam before. I have never heard of “water bathing” jam, so it should be fine.”
It doesn’t help that it’s largely the Americans who have invested in and come up with the modern research-based recommendations, because at some point the discussion always leaves science and facts far behind and it just becomes a bit of a pissing match (sorry but that is the best phrase) as Brits sputter that at the end of the day, they have no intention of adopting American ways.
In the instance of storing food in jars, however, the science does document the danger of improperly processed home bottled food products.
You can console yourself with knowing that there are some things Brits do that scare Americans — such as not refrigerating their eggs — that actually have solid science behind them: it’s safe for Brits to do that because Brits don’t wash their eggs the way Americans do, removing the protective coating on it.
Brits historically have always been on the alert for better food growing and preservation methods, willing to take any amount of effort to produce and preserve the best quality food in the best way possible, so there’s every reason to be hopeful that especially with the easy cross-exchange and trade of ideas today over the Internet that modern, better methods of home food preservation will gain a foothold as the younger generation displaces the older.
2. The “no one’s died yet” line
Home canning is just not as extensive in the UK as it is in North America. Consequently, sickness and illness outbreaks related to home canning are just not tracked in the UK as they are officially and specifically tracked in North America. Consequently, in the absence of tracking in this area, there is no data set.
In the UK, where the emphasis by far has been on commercially-produced food since the Industrial Revolution, food-related sickness and illness outbreaks are only tracked for commercially canned foods.
Not having heard of anyone getting ill from improperly home preserved food in Britain doesn’t mean anything — as these numbers are just not tracked or documented except in the rare instances that the issue happens to be identified as the big B word (botulism.)
The UK Food Standards agency regards home canning as an uncommon practice in the UK:
…home-canning is also quite an uncommon practice in the UK.”  Kirsten Stone, Microbiological Food Safety Branch, Food Safety: Hygiene & Microbiology Division, UK Food Standards Agency to Lisa Rayner. Email. Quoted in: Rayner, Lisa. The Natural Canning Resource Book. The Natural Canning Resource Book. Flagstaff, Arizona: Lifeweaver LLC. 2010. Page 64.
According to Moira Brett of the PHLS Central Public Health Laboratory in London,
….home preservation of non-acid foods such as meat, fish, and vegetables by methods other than freezing is actively discouraged and is now rare.”  Brett M. Botulism in the United Kingdom. Euro Surveill. 1999;4(1):pii=45. Accessed July 2015
Rare though it is, simply because home food preservation itself is so rare, people have died. Two people died in 1998 from home bottling mushrooms in oil.
(See: Botulism in the UK.)
But less dramatic illnesses owing to improperly processed home preserved food almost certainly also happen. That flu that everyone got at the Boxing Day get together at Aunt Beverley’s? It was actually the improperly home canned red currant jelly that grew mould that was just scraped off before being put out on the table, saying no one would be any the wiser.
3. The Women’s Institute (WI) has always done it this way
The WI, founded in Canada in 1897 ”The Women’s Institute (WI), a community-based organisation for women, was founded in Stoney Creek, Ontario, Canada by Adelaide Hoodless in 1897. It then expanded to Britain, and later to other countries.” Women’s Institutes. Wikipedia. Accessed 7 July 2016. , has been making jam in Britain since 1915 according to their records.  Updated NFWI advice on the reuse of jam jars. 4 January 2013. Accessed March 2013 at https://www.thewi.org.uk/media-centre2/news-and-events/past-news-and-events/updated-nfwi-advice-on-the-reuse-of-jam-jars
However, there are so many areas of health and food preparation and storage from 1915 that we wouldn’t dream of following now because they have been proven by science to be unsafe or dangerous. Food preservation is one of them.
Don’t use old books as your guides. Storing food in jars is a relatively modern art as far as human history goes, and we are still figuring it out, so what we know about it is still being updated — we know more now than they did in 1842 when the Kilner Jar company was founded, and if the Victorians and Edwardians had access to what we know now, you can bet the canny and prudent Victorians and Edwardians would take full advantage of it to profit by it.
Most WI recipes appear to be safe ingredient wise  https://www.thewi.org.uk/what-we-do/recipes/jams-and-other-preserves , but modern research-based science and practice says that they should be requiring water-bath processing for their bottled food products at the end to be safe for shelf-storage.
The trusted home food preservation book, So Easy To Preserve, explains what is wrong with the “open kettle” method still advocated by the WI:
An old out-dated method of canning — the open-kettle method — is now considered unsafe. In this method, foods were heated in a kettle, then poured into jars and a lid was placed on the jar. No processing was done. With this method there was often spoilage, because bacteria, yeasts and moulds that contaminated the food when the jars were filled were not killed by further processing. The growth of these microorganisms, in addition to spoiling the food, often caused lids that did seal to later come unsealed. This method results in a very real danger of botulism with low-acid foods or acid foods that experience mould growth.”  Andress, Elizabeth L. and Judy A. Harrison. So Easy to Preserve. University of Georgia Cooperative Extension. Bulletin 989. Sixth Edition. 2014. Page 18
4. Opinion trumping fact
For many people, their opinion trumps fact.
It’s understandable today in the food world, where various researchers race to the press with their latest findings in order to encourage their funders to keep the taps flowing, only for the press to run a contradictory story the following week by competing researchers — with a lazy press never bothering to challenge either. The result is that the term “food science” is rapidly becoming discredited today in some people’s minds.
But, the modern science behind canning / bottling — both home and commercial — is not part of these shenanigans. Yes, it is being refined continually, particularly in the home field. (For instance, adding a small amount of acid such as lemon juice to home-canned / bottled tomatoes has been required since 1994, and no sugar needed pectins for jams are now available.) But it is not part of the swiftly-changing “good for you, bad for you” circus, and shouldn’t be lumped in with that.
And confusingly, the same people who scoff at home canning / bottling safety-advice would never dream of licking a raw chicken from the supermarket, because that safety advice they take seriously.
Some typical questions that British home canners ask
1. What is processing a jar and does that apply to me in the UK?
To process your filled jars means to put the lids on them, and then “cook” the jars either fully submerged in a “water-bath” of boiling water, or, in a pressure canner at temperatures far exceeding the boiling point.
Many Brits starting to research home canning on the web are startled to learn that there’s even such as thing as processing your jars, and want to know if it’s just an American peculiarity.
The Australian national system (Fowler’s Vacola) and the German Weck jar system have both for over 100 years required a hot water bath process. All Canadian government advice since after the Second World War has required jars to be processed.
Kilner’s advice about water bathing appears to be either conflicting, or, in transition. Kilner says that water bath processing is only absolutely necessary if you are using their “clip top” (aka bail-type) jars (because they won’t seal otherwise), though their site shows their screw top lids being water bath processed as well.
It’s possible that safety concerns are starting to sway them. Much of their language is now taken from American safety advice, such as “Now your Kilner jars are closed you need to leave them to cool for 24 hours untouched. After the 24 hour cooling period you need to check your Kilner jars to make sure an airtight seal has formed….. If the lid moves, an airtight seal has not formed and you must reprocess your Kilner jars or eat the contents immediately.”
As of January 2014 (if not before), it might be that someone at Kilner is now calling for water bathing preserves including jams. See this video, particularly the mention of processing the Kilner jars as being important [at 2:03.]
Note though that as of summer 2016, other advice including recipe directions on the Kilner site still leaves out processing the jars.
Please note that water-bath processing only applies to low pH foods such as jams, jellies, conserves, relishes, chutneys, pickles, tomatoes (with added lemon juice for safety) etc, which is most of the preserving done in jars in the UK currently. Other food products such as soups, meat, plain vegetables etc must be processed in a pressure canner, no exceptions.
If your mind is still open to at least hearing the science behind why processing of filled jars is vital, here is the research:
D’sa, Elaine M. and Elizabeth L. Andress. Heat Processing of Home-canned Foods. National Center for Home Food Preservation. 22 December 2005. (Link valid as of May 2015.)
2. Why is sticking food in a bottle and just whacking a lid on unsafe?
The official term for this is “Open Kettle Canning.” It refers to just pre-cooking in a big open pot that people called a “kettle”, then just whacking the food stuff into a hot pre-sterilized jar, slapping a lid on, and if a seal happens, calling it job done. (It is an obscure term, to be sure, that no one understands.)
The process has been discredited by government home canning officials in North America since just after the end of World War Two, and discouraged, then finally officially recommended firmly against since 1989 as the evidence-based research and statistics of illness rolled in.
The fallacy in the logic is in the thinking that because the food was well and truly cooked and then put into clean jars, that you have a sterilized bottled product when you put the lid on.
The temperatures obtained in open kettle canning are not always necessarily high enough to destroy all spoilage and food poisoning organisms that may be in the food, depending on the food product. Also, microorganisms can enter the food when it is transferred from the kettle to jar and cause spoilage. They may also be floating by in the air that gets sealed into the jar when the lid is put on. There, the micro-organisms have a safe moist environment with lots of tasty food to begin flourishing. And remember, mould is not always of the visible kind.
Just because a seal on the jar is obtained does not indicate that a canned product is safe. A seal indicates that new contaminants cannot get in, but it tells you nothing about the presence of microorganisms (mould, yeast, bacteria) that snuck into the jar as the lid was lowered on it. Heat from a proper canning process is needed to make sure any microorganisms in the jar of food are killed.
The authors of Putting Food By say,
Mold is one of the leaders in the air-borne danger brigade, and it can settle on the underside of a canning lid and grow. In the process of growing it can metabolize the safe margin of acid just enough to allow surviving C. botulinum spores to develop and throw off their wicked toxin. So your jar of supposedly “safe” open-kettle-canned tomatoes—or dill pickles or jams or condiments or pears or peaches, all of which traditionally have been regarded as strong-acid enough to be protected—may contain a deadly threat. And aside from botulism, there could be mycotoxins from mold itself.”  Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (pp. 60-61). Penguin Publishing Group. Kindle Edition.
The USDA Food Safety Information says,
Yes, molds can thrive in high-acid foods like jams, jellies, pickles, fruit, and tomatoes. But these microscopic fungi are easily destroyed by heat processing high-acid foods at a temperature of 212 °F [100 c] in a boiling water canner for the recommended length of time.”  USDA Food Safety Information. Molds on Food: Are They Dangerous? August 2013. Accessed March 2015 at https://www.fsis.usda.gov/wps/wcm/connect/a87cdc2c-6ddd-49f0-bd1f-393086742e68/Molds_on_Food.pdf
What can survive high acidity in an unprocessed jar? Well, e-coli, listeria and salmonella are a few examples.
“While these pathogens [Escherichia coli O157:H7, Salmonella enterica, Listeria monocytogenes and other pathogenic bacteria] do not grow in acidified vegetables, they may survive long enough to cause disease. The infectious dose for E. coli O157:H7 may be as low as one to ten cells. For this reason, acidified vegetables must be processed to assure a five log reduction in acid resistant pathogenic bacteria….E. coli O157:H7 has been found to be the most acid resistant pathogen of concern for these products….The research done here documents how innocuous items such as pickled onions could hold E. coli that aren’t immediately killed by the vinegar, and what must be done to ensure its destruction.”  Bredit, Frederick, et al. Use of Linear Models for Thermal Processing of Acidified Foods. In: Food Protection Trends, Vol. 30, No. 5, 2010. Pages 268–272. Accessed March 2015.
Ever got Delhi belly after eating someone’s home preserves and wonder where on earth you could have picked it up? You may have been lucky.
Here’s some further reading about the dangers of the Open Kettle Canning that is practised in the UK, if you aren’t leaping out of your jar with outrage just yet:
Penn State Extension. Avoid … Open Kettle or Oven Canning. 29 Mary 2014. (Link valid as of May 2015)
3. Surely all the sugar is enough of a preservative?
Do not rely on sugar to make your product safe.
Sugar has anti-spoilage properties quality-wise but don’t rely on it to keep food safe health-wise. Its primary purpose in canning is taste, and thickening (for instance, by interacting with pectin in jams), as well as maintaining texture and coloration.
“Despite the high-acid content of fruit and the large quantities of sugar that are used to make jellied products, mold growth often occurs on the top.”  Boyer, Renee R. and Julie McKinney. Boiling Water Bath Canning: Including Jams, Jellies, and Pickled Products. Virginia Cooperative Extension. Pub No. 348-594. 2013. Page 12. Accessed March 2015 at https://pubs.ext.vt.edu/348/348-594/348-594_pdf.pdf
Only in a few, very rare recipes and instances is sugar used in such extreme quantities as to actually deny water activity to bacteria and thus make a product safe in its own right.
Don’t assume that sugar / vinegar / pre-sterilized jars is a good enough preservative. Assumptions can be dangerous, and doubly so if they are stubbornly held in the face of research-based science that has already proven them wrong.
4. What is the danger?
Basically, you can presume that many jars of home preserved products have botulism spores in them, but the botulism is unable to cause any harm because of the low pH (aka high acidic level) of the products.
Moulds in the jars, seen and unseen, can raise the pH of your jam or pickle above the pH safety level of 4.6, allowing botulism spores to finally spring to life, producing their deadly toxins as a byproduct. Mould spores, which live in the millions in the air between the filled jar and the lid you are about to put on the jar, are killed off in the jar during heat processing of the jar.
The authors of Putting Food By explain what happened to one family when mould spores in a jar of tomato weren’t killed off by heat processing of the jar:
…early in 1974 there were two deaths from botulism poisoning traced directly to home-canned tomatoes and tomato juice…. Meanwhile the public health officers discovered what actually allowed the spores of C. botulinum to make the toxin that killed the victims. Common bacteria or molds grew in the food in the jars and thereby reduced the acidity because the natural acid in the tomatoes was metabolized by the micro-organisms as they grew and developed. It was established after compassionate, but thorough, investigation that these bacteria or molds survived either because the tomatoes were canned by the discredited open-kettle method, or entered under the lid of a jar that wasn’t adequately sealed. Inadequate processing is virtually always the cause of food poisoning that develops during shelf life.”  Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 119-120). Penguin Publishing Group. Kindle Edition.
Above all, remember: “It is not safe to remove the mould and eat the food, because certain types of mould reduce the acidity to a point where botulinus spores may develop.”  Cameron, Janet L. and Mary L. Thompson. Canning for the Home. Bulletin No. 128. Virginia Agricultural and Mechanical College and Polytechnic Institute and the United States Department of Agriculture, Cooperating Extension Division. Revised June 1944. Page 5.
The Virginia Cooperative Extension says,
“Recent recommendations from the USDA say that products that contain mold growth should be discarded. Mycotoxins, which are chemical substances produced by molds during growth, are known to cause cancer in animals.”  Boyer, Renee R. and Julie McKinney. Boiling Water Bath Canning: Including Jams, Jellies, and Pickled Products. Virginia Cooperative Extension. Pub No. 348-594. 2013. Page 12. Accessed March 2015 at https://pubs.ext.vt.edu/348/348-594/348-594_pdf.pdf
5. Many people get “24-hour flu” and never realize it’s from a simple bottle of homemade jam
While the “B word” is the most deadly that can happen, it’s actually other milder nasties that are far more common. Many people often get a “gippy tummy” for reasons that they can’t fathom, and attribute it to a “24-hour flu”. However, there’s actually no such thing as 24-hour flu: it’s food poisoning.
Some of the more common pathogens in improperly processed home canned foods can include Staph. aureus, Clostridium perfringens, C. botulinum, Campylobacter, Listeria, Bacillus cereus, E. coli, and Vibrio (parahaemolyticus).
Of these, the most common apparently is E. coli:
“The primary public health concern associated with …. with acid or acidified canned foods the threat to public health is from Escherichia coli O157:H7 (Breidt et al. 2010) or Listeria monocytogenes (Breidt et al. 2014).”  Etzel, M. R., Willmore, P. and Ingham, B. H. (2014), Heat penetration and thermocouple location in home canning. Food Science & Nutrition. doi: 10.1002/fsn3.185. https://onlinelibrary.wiley.com/doi/10.1002/fsn3.185/full
Some people’s bodies might be able to process the pathogens without incident, if they are healthy adults, or just get a bit of “Delhi Belly” or think they had a mild case of the flu, but for people are have comprised or weak immune systems (older people, children, people on chemo, etc), it could be very dangerous.
These other nasties are all dealt with handily by simply processing your filled jar.
6. I’m okay with taking any “apparent” risk
That’s your decision.
Your body, your safety choice.
However, you don’t have the right to impose that risk on others. Consume improperly canned food yourself and don’t feed it to anyone else. The open kettle / “just bottling” method has been proven decades ago in labs to be not safe.
Here’s a quote from a discussion group about assuming home canning risks:
I simply won’t take the chance with myself, my loved ones or friends I gift my home canned foods to, by giving them home products canned with questionable outdated methods. I can’t imagine how anyone might feel that gifted that one jar that carried botulism spores not destroyed during processing. It’s just not worth it….I too, jarred up jellies with wax years ago and scooped out the mold. Now, I process them in a hot water bath. It’s just safer as well as not messing with hot wax and it looks better. I also feel better about gifting it for the holidays.”  User Rosey. Comment posted on 11 October 2013. Accessed March 2015 at https://www.hillbillyhousewife.com/oven-canning-method.htm/comment-page-4#comment-45764
The kicker: doing your home canning safely is actually less work
It’s actually less work for you to water bath process your filled jars than to do it the old unsafe way.
The Killner company still advises the old way (with and without a water bath), which is that you sterilize your jars first for 10 minutes, then separately sterilize your lids for 10 minutes in another pot.
Up-to-date lab-based research, and official, government-backed advice based on this research, has some good news for you: NEITHER of those steps is necessary anymore for anything being processed in a hot water bath for 10 minutes or more (or being pressure canned): the sterilization will happen anyway as part of the processing.
So instead of spending time futzing to sterilize the lids and jars, separately, it’s actually less work to do it the right way, and sterilize everything all together as a whole at the end of the process. You’re just shifting that sterilization work to the end of the process and saving some futzing while you’re at it.
It saves money, it saves time, it reduces your carbon footprint, it guarantees safety, and it delivers better food quality — who in their right mind would object?
And wax tops and wax sealers? Completely unsafe. But it was such a messy process anyway, who would miss it? Use the 2-piece Mason jar lids instead for ease and safety, as sold by Kilner (their preserving line), Leifheit, le Parfait Famillia Wiss, or Ball.
The science is clear, and it’s less work. Now go away and mutter about how the WI still does it the old way and no one’s been killed yet (that you’ve heard of personally) and you’ll be darned if you’ll let foreigners suggest how Brits should do things — after all, everyone knows the natural order is the other way round!
But think about it — it’s less futzing, it’s safer, and it gives a higher-quality product. And, again: It. Is. Less. Futzing.
References [ + ]
|1.||↑||Bernardin Guide to Home Preserving. Toronto, Canada: Bernardin Ltd. 2013, page 4|
|2.||↑||Andress, Elizabeth L. and Judy A. Harrison. So Easy to Preserve. University of Georgia Cooperative Extension. Bulletin 989. Sixth Edition. 2014. Page 18|
|3.||↑||Wartime Garden and Kitchen, BBC. With Harry Dodson, Ruth Mott, et al. Episode 6. 1993. Start time: 16:23.|
|4.||↑||Kirsten Stone, Microbiological Food Safety Branch, Food Safety: Hygiene & Microbiology Division, UK Food Standards Agency to Lisa Rayner. Email. Quoted in: Rayner, Lisa. The Natural Canning Resource Book. The Natural Canning Resource Book. Flagstaff, Arizona: Lifeweaver LLC. 2010. Page 64.|
|5.||↑||Brett M. Botulism in the United Kingdom. Euro Surveill. 1999;4(1):pii=45. Accessed July 2015|
|6.||↑||”The Women’s Institute (WI), a community-based organisation for women, was founded in Stoney Creek, Ontario, Canada by Adelaide Hoodless in 1897. It then expanded to Britain, and later to other countries.” Women’s Institutes. Wikipedia. Accessed 7 July 2016.|
|7.||↑||Updated NFWI advice on the reuse of jam jars. 4 January 2013. Accessed March 2013 at https://www.thewi.org.uk/media-centre2/news-and-events/past-news-and-events/updated-nfwi-advice-on-the-reuse-of-jam-jars|
|9.||↑||Andress, Elizabeth L. and Judy A. Harrison. So Easy to Preserve. University of Georgia Cooperative Extension. Bulletin 989. Sixth Edition. 2014. Page 18|
|10.||↑||Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (pp. 60-61). Penguin Publishing Group. Kindle Edition.|
|11.||↑||USDA Food Safety Information. Molds on Food: Are They Dangerous? August 2013. Accessed March 2015 at https://www.fsis.usda.gov/wps/wcm/connect/a87cdc2c-6ddd-49f0-bd1f-393086742e68/Molds_on_Food.pdf|
|12.||↑||Bredit, Frederick, et al. Use of Linear Models for Thermal Processing of Acidified Foods. In: Food Protection Trends, Vol. 30, No. 5, 2010. Pages 268–272. Accessed March 2015.|
|13.||↑||Boyer, Renee R. and Julie McKinney. Boiling Water Bath Canning: Including Jams, Jellies, and Pickled Products. Virginia Cooperative Extension. Pub No. 348-594. 2013. Page 12. Accessed March 2015 at https://pubs.ext.vt.edu/348/348-594/348-594_pdf.pdf|
|14.||↑||Hertzberg, Ruth; Greene, Janet; Vaughan, Beatrice (2010-05-25). Putting Food By: Fifth Edition (p. 119-120). Penguin Publishing Group. Kindle Edition.|
|15.||↑||Cameron, Janet L. and Mary L. Thompson. Canning for the Home. Bulletin No. 128. Virginia Agricultural and Mechanical College and Polytechnic Institute and the United States Department of Agriculture, Cooperating Extension Division. Revised June 1944. Page 5.|
|16.||↑||Boyer, Renee R. and Julie McKinney. Boiling Water Bath Canning: Including Jams, Jellies, and Pickled Products. Virginia Cooperative Extension. Pub No. 348-594. 2013. Page 12. Accessed March 2015 at https://pubs.ext.vt.edu/348/348-594/348-594_pdf.pdf|
|17.||↑||Etzel, M. R., Willmore, P. and Ingham, B. H. (2014), Heat penetration and thermocouple location in home canning. Food Science & Nutrition. doi: 10.1002/fsn3.185. https://onlinelibrary.wiley.com/doi/10.1002/fsn3.185/full|
|18.||↑||User Rosey. Comment posted on 11 October 2013. Accessed March 2015 at https://www.hillbillyhousewife.com/oven-canning-method.htm/comment-page-4#comment-45764|