Why Allow Headspace?
Posted: September 14, 2012
Next scenario—you are filling jelly jars and need just a little more jelly to make another jar. If you take just a little from each of the other jars, you will have that extra jar—WHOA! The processing time may not be long enough to drive out all that extra air from the top of the jar resulting in a poorly formed vacuum seal. Besides, the extra air left inside the jar could cause the food to discolor.
Headspace in Canned Foods
Headspace is the space in the jar between the inside of the lid and the top of the food or its liquid. Allow ½ inch headspace for tomatoes, pickles, and fruits. Vegetables need one inch headspace to allow for the expansion of the starch in the vegetable. Allow one inch headspace for red meats and 1¼ inch for poultry. Most jelly and jam recommendations are for ¼ inch headspace. Some jams made with artificial sweeteners need greater headspace. Occasionally use a ruler to check the accuracy of the headspace. Not all jars are shaped the same so that you can’t count on a certain groove or the neck of the jar being a set distance from the rim.
The headspace you start with may not be the same as when you finish. Foods that are packed into jars hot may shrink when cooled. Air spaces in raw packed foods rise to the top of the jar when heat processed and may increase headspace. Finally, siphoning may cause the loss of liquid in jars. Raw packing food and using heavy sugar syrups increase siphoning. Loss of liquid can be reduced by allowing the jars to sit in the canner 5 minutes after processing is completed before removing the jars from the canner. If liquid is lost during processing and the jar is sealed, do not open the jar to replace the liquid. Liquid loss is not a sign of spoilage.
Headspace in Frozen Foods
Headspace is also needed for frozen foods with a high moisture content. Liquid expands when frozen causing syrup to overflow (and cause a mess in the freezer). Headspace varies by the type of pack and the size of the container. Fruit packed in juice, sugar, syrup, or water as well as crushed or pureed fruit should have ½ inch headspace in wide top pint containers and 1 inch headspace in wide top quart containers. The same products should have ¾ inch headspace in pint containers with a narrow opening or 1½ inches in a quart container with a narrow opening. Juice needs 1½ inches headspace in all narrow jars. Fruits and vegetables packed without added sugar or liquid only need ½ inch headspace in either pint or quart containers regardless of opening size. Vegetables that pack loosely have space to expand between the food pieces and don’t need extra headspace. This includes asparagus, broccoli, cauliflower, Brussels sprouts, cauliflower, peppers, and foods that are individually quick frozen (also called tray packed.)
For more information on home food preservation visit http://extension.psu.edu/food-safety/food-preservation