Headspace is the space between the top of the food and the rim of the canning jar.
During processing, the heat causes the contents of the jar to expand. Air escapes around the two piece lid. To ensure proper sealing, only two piece lids should be used for home canning. One piece lids are designed for commercial canning equipment.
After Processing, the contents of the canning jar contract as they cool and the lid is pulled down tight and the jar seals itself.
If you don't have enough headspace, the food might seep under the lid as the food expands and interfere with sealing.
If you have too much headspace, the processing time specified in the recipe may not be long enough to dirve out the air. This can also interfere with proper sealing of the canning jar.
Good canning recipes specify the headspace, but a general rule of thumb is use 1 inch for low acid foods (such as vegetables), 1/2 inch for fruits, and 1/4 inch for jams and jellies.
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Three Ingredient Fig Jam for Canning
1 year ago
Okay Charlotte, my goal this fruit season is to actually put something up. I'm going to use your expertise, so hold me to it. It's been a goal for a while, but I don't have anywhere to store anything in my little apartment! ha ha, no more excuses!
ReplyDeleteCharlotte,
ReplyDeleteDo you know what happens if I leave too much headspace? Will the jars at least un-pop if my food is unsafe? I just hate to think about consuming potentially unsafe food...and I know my salsa that I canned last week had too much headspace, plus I had a quart jar of diced tomatoes and only a pint of tomatoes left, so I just canned it. But it's been sitting on my counter making me nervous ever since. Maybe I should move it to the fridge?
Thank you!! Katie
What will happen if I leave too little or too much headspace? Thanks! You really write articles with good content. Keep it up.
ReplyDeleteKatie, I asked this question of a Master Food Preserver recently and he said that jars that aren't full will have a weaker vacuum seal, and may retain enough oxygen for oxidation to occur on the surface of the food.
ReplyDeleteAdditionally, because air is an insulator and does not heat up as fast as a liquid, it is possible that bacteria might survive the processing.
Unlikely, but possible. He recommends always following the headspace instructions for tested recipes. If you have less than a full jar, use a smaller jar, or simply refrigerate the excess product.