food-preservationfreezingjam
I have read on multiple canning sites that you can freeze jam in glass jars. Has anyone actually done this successfully? Under what circumstances would it be preferable to putting the jam in plastic containers?
It just doesn't seem very safe to me (I fear the glass would break).
Previously, I have bought plastic containers to freeze jam in, but they did not seal very well. I'm wondering if glass could perform better? Or, should I just find better plastic containers?
A lot of dairy products become watery or start to separate if they've been frozen or defrosted: pastries with cream fillings, cream cheese, sour cream.
The USDA says does not recommend that eggs or canned foods be stored frozen. Eggshells can crack easily, and even if the shells remain intact, the consistency of egg yolks makes them difficult to use for anything other than hard-boiling. Canned foods that are frozen accidentally could pose health risks, so the USDA recommends inspecting to see if the can has rusted or burst. If the can is swollen, thaw it but check to make sure it doesn't look or smell off before eating.
The FDA also has a useful chart (pdf) on which foods don't freeze well and how long you can freeze other foods. (Note: when there is a recommended limit on how long a food should be frozen, it indicates when the quality of the food will decrease - NOT when it will "expire". You could theoretically freeze most foods indefinitely.)
The only other thing I would avoid freezing is any sort of raw green (lettuce, spinach, etc.). Greens wilt and turn brown when you freeze them. (If they're cooked, they should be fine to freeze and thaw.)
EDIT: Apparently, some spices become bitter when frozen, including pepper, cloves, garlic, green pepper, imitation vanilla, and onions, paprika and celery taste different.
You just need to work out your forearms more. :)
If food gets on the rim of the jar it can greatly add to the friction after the lid is on. It actually makes the whole process unreliable- the food might prevent a seal from forming or it might harden and make the lid difficult to remove- either way make sure the rim of the jar is clean.
Canning jars create a vacuum when the heated air in the jar contracts. This vacuum is what holds the lid on tightly. You can alter the strength of the vacuum in two ways:
1- leave more air at the top of the jar (called headspace).
More air means that a smaller percentage of the air will be forced out and the seal will be weaker. Be careful that you don't make it too weak. If the seal fails the food will spoil.
Jam recipes meant for normal canning jars will include the recommended headspace. You should start there with your experiments.
2- Let the jam cool a little before applying the lid.
This will also result in less air being forced out and a weaker seal. This is something you can experiment with but it would be more finicky than #1. If you do try it, watch your jars closely for a while and put them in the fridge if the seal fails.
The canning process for jam in normal canning jars usually includes boiling the jars afterwards to ensure the jars seal properly. With those lids, sealing too strongly isn't a concern as the lids are disposable. Even with your jars, you want a very strong seal. If you are having trouble opening them perhaps you should try using a tool that will give you leverage but not damage the lid.
Best Answer
Yes, I've done this. The key is to ensure that the jam isn't filling the glass container completely so that as it freezes it has room to expand.
I used a typical Ball canning jar, which sealed well enough to keep ice crystals out for several months.
From what I understand, freezer canning is useful when you don't have a pressure canner but want to can lower acid items which otherwise might be dangerous to your health (if not pressure canned).