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.
I had a student ask me a very important question the other day. “How long will the jam last after I open it and put it in the refrigerator?” I am so happy they asked this question. First, you may want to make jam in half pint sized jars so it won’t have enough time to go bad. You’ll eat it before it has time to spoil! I can with half-pint jars because sometimes, I get board eating the same canned goods – I want a different flavor. Sugar is the number one preservative in canned goods but sugar is not always a healthy choice. I use less sugar in my recipes which means that my jams and canned goods will have less preservatives and ultimately a shorter shelf life. I would prefer to healthy, great tasting food than have food that lasts forever.
You should always use clean utensils when canning. So many of us spread butter with a knife and then dip that same knife in the jam jar without realizing we have just contaminated the jam with foreign bacteria. That is how mold starts to grow in the jar. My personal rule for jams made with less sugar is 2 months in the refrigerator after being opened (but I’m sure you will eat them before then).
See you in class