Canning FAQ

Commonly Asked Questions

Find answers to commonly asked questions about canning food at home. Explore additional resources on canning as a food preservation method through the National Center for Home Food Preservation or contact an Illinois Extension expert to learn more.
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Canning Questions

Must I add lemon juice to my tomatoes?

Yes. This is an important step to ensure safe acidity in whole, crushed, or juiced tomatoes. Acid can be added directly to the jars before filling with the product. 

Amounts of Added Acid for Canning Tomatoes
 

Bottled Lemon Juice

Citric Acid 

For Quarts

2 Tablespoons

½ teaspoon

 For Pints

1 Tablespoon

¼ teaspoon

Substitution

Four tablespoons of a 5% acidity vinegar per quart may be used instead of lemon juice or citric acid. However, vinegar may cause undesirable flavor changes.

Can food be re-canned if the lid does not seal?

Yes, if discovered within 24 hours. To re-can, remove the lid and check the jar rim for nicks. Change the jar, if nicks are present, add a new lid and reprocess using the original processing time.

How long will canned food keep?

Home canned food will retain optimum quality for one year. 

Is it necessary to sterilize jars before canning?

Sterilizing jars before canning is necessary only if the jars are to be processed in a water bath and only if the processing time is less than 10 minutes.

Is it safe to reduce or double a recipe?

Do not alter recipes unless all ingredients can be divided evenly in half or doubled exactly, with no rounding or fractional amounts. Look for various batch-size recipes from USDA, NCHFP, Extension, or commercial canning supply companies.