So you have decided to try your hand at canning. You've chosen a recipe that you want to use and you notice that it specifies the amount of headspace to leave when filling the jar. If you are new to canning, this might seem excessively picky. You might think, "Does it really matter? My food will taste the same regardless of the amount of empty space that I leave at the top of the jar."

The answer is, "Yes, it does matter." During processing (either in a water bath or a pressure canner), the heat causes the contents of the jar to expand. Air escapes around the two piece lid.  If you don't have enough headspace, the food might seep under the lid as the it expands. This would interfere with sealing.

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 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.

Charlotte originally fell in love with home canning as a child by helping her mother can food. She later came to be especially fond of canning unique flavors of jam. She shares her knowledge about canning, by writing a blog (Canning Jars Etc.)that includes basic instructions for home canning and canning recipes.