Why Some Old Canning Recipes Are No Longer Safe

In canning books and handouts from several decades ago, you might come across recipes that are no longer safe today. That is because, based on new laboratory research, certain recipes have been withdrawn and updated. The seminal home preservation book So Easy to Preserve is a good indicator of changes made to recipes over time. The book was first published in 1984; it has gone through six editions, and the latest update came out in 2020.

Here are some examples of recipes that have been withdrawn or changed:

Canned Bread or Cake

The term "canned" is misleading because the bread or cake isn't canned; it is baked in open canning jars, and after removing it from the oven, the jars are closed with a canning lid. The ingredients make it a low-acid food with a pH above 4.6. It provides a high-moisture environment where pathogenic microorganisms can grow, which can lead to the development of the botulism toxin. Also, it is not safe to use canning jars in dry oven heat, which can cause thermal cracking.

The protocol for commercially sold canned bread, such as Boston brown bread, is very different from home-canning bread. The store-bought product also contains additives and preservatives to control microbial growth.

White Peaches and Elderberries

Due to new research on their acidity, in So Easy to Preserve, the chapters about canning fruit no longer include white peaches and elderberries.

With a pH of above 4.6, white peaches are a low-acid fruit, and neither water bath canning nor atmospheric steam canning is able to destroy the harmful bacteria that can grow in them. A pressure canning process is not available for white peaches to determine safety and quality issues. Today, it is recommended to freeze white peaches.

The same applies to elderberries. Their average pH of 4.92 creates similar safety issues. But, there is one exception: elderberry jam or jelly. It is required that you precisely weigh the ingredients, and for every 16 ounces of elderberry pulp, you add at least 18.9 ounces of sugar. For making jelly, for every 16 ounces of elderberry juice, you add at least 19.5 ounces of sugar.

Canning Tomatoes

Two significant changes have been made to recipes for canning tomatoes.

Acidification: Updated recipes call for bottled lemon juice or citric acid to ensure a consistent level of acidity. One tablespoon of bottled lemon juice or ¼ teaspoon of citric acid powder must be added to a pint jar, or two tablespoons of bottled lemon juice or ½ teaspoon of citric acid must be added to a quart jar before filling the jar with tomatoes.

It is important to note that all tomato varieties are borderline in acidity and therefore require acidification for canning. Some newer tomato varieties, especially yellow and orange tomatoes, may taste less acidic because they contain more natural sugars that mask the acidic taste. The color of tomatoes and whether they are heirloom tomatoes or hybrids does not affect their acidity.

Process times: Today, tomatoes are processed longer than they used to be. For example, the recommended process time in a boiling water bath for whole or halved tomatoes, packed raw without added liquid, is 85 minutes at an altitude up to 1,000 feet and increases by 5-minute steps for higher altitudes.

Using Paraffin Wax to Seal Jars

Paraffin or wax seals, which were once used for sealing jellies and jams, are no longer considered safe, although the products are still sold in retail stores. The paraffin shrinks over time, and temperature changes make the canned product susceptible to the growth of molds and yeasts.

Thickening Pie Fillings with Modified Starch instead of Cornstarch or Flour

National Starch Company released a modified starch under the brand name ClearJel® in the 1940s. It has a smooth texture, and unlike conventional starches, it allows the heat to penetrate any cold spots in the jar. According to Tom Dimick, Outreach Coordinator in the Department of Food Science at Penn State University, it was during the mid-1980s that Gerald Kuhn, at the Center for Excellence in Home Food Preservation in the College of Agriculture at Penn State University, developed and tested recipes using ClearJel that were subsequently released to the public.

ClearJel is resistant to breaking down under the high heat that a pie filling is exposed to three times: during the preparation of the pie filling for canning, during the canning process, and during the baking of the pie. The product does not thicken until it cools. ClearJel is suitable for high-acid foods such as canned apple pie filling.

Another modified food starch product for canned pie fillings is ThermFlo®, which is suitable for high- and low-acid foods.

Both products should only be used in scientifically tested recipes that call for them and only in the amount specified in the recipe.

The above procedures illustrate the pitfalls of older canning recipes and underline the importance of using only current tested recipes from a credible source, such as Penn State and other Extension Services, the USDA Complete Guide to Home Canning, and other information put out by the National Center for Home Food Preservation, and the latest edition of the book, So Easy to Preserve.

References

Kralj, R. (2015, March 12). Food Preservation: Setting the Record Straight on Canning Breads and Cakes. Penn State Extension. Retrieved July 27, 2021.

Morrow, J. (2020, June 30). Preserving White Peaches. Penn State Extension. Retrieved July 27, 2021.

Ingham, B. (2020, June 5). Elderberries: beautiful to look at, not for canning. University of Wisconsin Division of Extension. Retrieved July 27, 2021.

Zepp, M. (2019, July 17). Canning Tomatoes: Do's and Don'ts. Penn State Extension. Retrieved July 27, 2021.

Hirneisen, A., LaBorde, L., Zepp, M. (2019, March 13). Let's Preserve: Fruit Pie Fillings. Penn State Extension. Retrieved July 27, 2021.

Zepp, M. (2020, March 2). Modified Food Starches. Penn State Extension. Retrieved July 27, 2021.