Canning

Is it safe to can food without salt?

Yes. Salt is used for flavor only and is not necessary to prevent spoilage.

Is it safe to can fruits without sugar?

Yes. Sugar is added to improve flavor, help stabilize color, and retain the shape of the fruit. It is not added as a preservative.

Can fruits and vegetables be canned without heating if aspirin is used?

No. Aspirin should not be used in canning. It cannot be relied on to prevent spoilage or to give satisfactory products. Adequate heat treatment is the only safe procedure.

Is it safe to can green beans in a boiling water bath if vinegar is used?

No. Recommended processing methods must be used to assure safety. Recommended processing times cannot be shortened if vinegar is used in canning fresh vegetables (this does not refer to pickled vegetables).

Should all vegetables be precooked before canning?

For best quality, yes. However, some vegetables can be packed raw or cold into jars before being processed in the pressure canner.

What vegetables expand instead of shrink during processing?

Corn, peas and lima beans are starchy and expand during processing. They should be packed loosely.

What causes corn to turn brown during processing?

This occurs most often when too high a temperature is used causing caramelization of the sugar in the corn. It may also be caused by some minerals in the water used in canning.

Why is canning summer squash or zucchini not recommended?

Recommendations for canning summer squashes, including zucchini, that appeared in former editions of So Easy to Preserve or USDA bulletins have been withdrawn due to uncertainty about the determination of processing times. Squashes are low-acid vegetables and require pressure canning for a known period of time that will destroy the bacteria that cause botulism. Documentation for the previous processing times cannot be found, and reports that are available do not support the old process. Slices or cubes of cooked summer squash will get quite soft and pack tightly into the jars. The amount of squash filled into a jar will affect the heating pattern in that jar. It is best to freeze summer squashes or pickle them for canning, but they may also be dried.

Can I can my own salsa recipe?

Salsas are usually mixtures of acid and low-acid ingredients; they are an example of an acidified food. The specific recipe, and sometimes preparation method, will determine if a salsa can be processed in a boiling water canner or a pressure canner. A process must be scientifically determined for each recipe. To can salsa at home, use our recipes for Hot Chile Salsa or Mexican Tomato Sauce. Your county Extension agent may have additional tested recipes for salsas.

Can you provide a process time for pumpkin butter?

In accordance with USDA recommendations, the University of Georgia Cooperative Extension does not have a recommendation for canning pumpkin butter at home.  The desired research has not been done to allow establishing safe processing times for this type of product which generally consists of pureed pumpkin, spices and some sweetener cooked to a thickened, spreadable fruit butter consistency. Some recipes may have some added acid ingredients, but we do not have access to research data that shows what proportions and parameters are needed for proper acidification for boiling water canning like acid fruit butters. If it is a recipe considered to result in a low-acid butter, then we do not make up or estimate low-acid canning processes.

Regardless of acidity, a canning process for such a product would either need to be recipe-specific or take into account what recipe would provide the greatest challenge to safe canning.  It is not possible to evaluate a pumpkin butter recipe for canning recommendations by looking at it at this time.  Some of the factors that are critical to the safety of canned pureed pumpkin products are the viscosity (thickness), the acidity and the water activity (or amount of water available to microorganisms after production).  Pumpkin is naturally a low-acid food for canning considerations (pH>4.6), capable of supporting the growth of Clostridium botulinum bacteria which can cause the very serious illness, botulism, under the right storage conditions.  If the bacteria are present and survive processing, and the product has a high enough water activity, they can thrive and produce toxin in the product.  Even if the pumpkin butter would be acidified to less than pH 4.6 to control for botulism, the consistency would require studying for its effect on heat penetration throughout the jar during processing to control for other bacterial concerns.

At this point, the investment has not been made into research desired for a home canning pumpkin butter recommendation. It is best to make pumpkin butters fresh for shorter refrigerator storage, or to freeze them.  We do not have a process we can recommend.

Why do you say not to can mashed or pureed pumpkin or winter squash?

Home canning is not recommended for mashed or pureed pumpkin or winter squash.  While there were directions in older, now historical USDA publications, they were withdrawn after expert review with publication of the Complete Guide to Home Canning in 1989. This remains the basis of Extension recommendations today, even with updated versions of this book. There has not been investment in the research desired to offer a home canning process. USDA publications prior to 1989 that had directions for canning mashed winter squash are now considered out-of-date. 

The USDA processing recommendation for pumpkin and winter squash should only be used with squashes cut into 1-inch cubes.  Pureed or mashed pumpkin can be frozen for long term storage.

A review of many USDA vegetable canning processes with studies conducted at the University of Minnesota in the 1970's indicated that there was too much variation in viscosity among different batches of prepared pumpkin purees to permit calculation of a single processing recommendation that would cover the potential variation among products (Zottola, et.al., 1978). USDA subsequently decided to withdraw their old recommendation; unfortunately, no further research has been conducted to determine a home canning recommendation. Pumpkin and winter squash are low-acid foods (pH>4.6) capable of supporting the growth of Clostridium botulinum bacteria which can cause the very serious illness, botulism, under the right storage conditions.  If the bacteria are present and survive processing, and the product has a high enough water activity, they can thrive and produce toxin in the product.

Reference: Zottola, E. A., Wolf, I.D., Norsiden, K.L. and D.R. Thompson.  1978.  Home canning of food: Evaluation of current recommended methods.  Jn. of Food Science 43:1731.