I received another great question from a student. Their question was, “When I’m canning and I only have enough food left to fill half of a jar, do I process that jar that is only filled up half way?” The answer is no. Every recipe has a head space recommendation which needs to be carefully followed. As a general rule, leave 1 inch of head space for low-acid foods like vegetables and meats (when you are pressure canning); leave 1/2 inch head space for high-acid foods like fruits, tomatoes, pickles, and relishes; 1/4 inch head space for jams and jellies. Care must be taken when filling jars to the correct head space. To much air can turn food a dark color and may cause it to begin to mold. To much food in a jar can cause the jar to break in the water bath during processing. If you have a jar that is only half full, put it in the refrigerator and eat it first.
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