Wash berries in batches of 1 or 2 litres (quarts) at a time.
Drain, and get any stems off.
Have a pan of water boiling.
Add the berries in small batches at a time so that the water will come back to the boil quickly.
Let the berries boil for 30 seconds, then fish out of pot immediately with slotted spoon or sieve.
Repeat until all berries are blanched.
Divvy berries out amongst jars, leaving 2 cm (½ inch) headspace.
Divvy blanching juice out amongst jars, leaving 2 cm (½ inch) headspace.
If short of canning liquid, top jars up with boiling water from a kettle.
Debubble, top up with more liquid as required to retain headspace.
Wipe jar rims.
Put lids on.
Process jars in a water bath or steam canner for 15 minutes (all jar sizes); increase time as needed for your altitude.
Notes
[Optional] Per ¼ litre (½ US pint) jar, ⅛th teaspoon liquid stevia. Per ½ litre (US pint), ¼ teaspoon liquid stevia. Per 1 litre (US quart) jar, ½ teaspoon liquid stevia.Start out with only a small amount of blanching water, just enough to cover the berries, because as you blanch the berries they will release juice and the amount of liquid will increase. That way, you end up with purer and less watered-down juice to use for packing the berries in.The small ¼ litre (1 cup / ½ US pint / 8 oz) jars are handy for baking; you may wish to can some of those at least unsweetened for maximum flexibility when you go to use them.