Newsflash

Newsflash

Canning in Electric Multi-Cookers

Should I can in my electric multi-cooker appliance?

Even if there are instructions for pressure canning in the manufacturer’s directions, we do not support the use of the USDA canning processes in the electric, multi-cooker appliances now containing "canning" or "steam canning" buttons on their front panels.  Our pressure process directions have not been developed for that type of appliance, and the canner being used does matter. Our recommendations were determined for stovetop pressure canners which hold four or more quart-size jars standing upright. 

We do not know if proper thermal process development work has been done in order to justify the canning advice that is distributed with these pressure multi-cooker appliances. What we do know is that our canning processes are not recommended for use in electric pressure multi-cookers at this time. 

Some of the major reasons we cannot recommend using electric multi-cookers for pressure canning:  

1.  Thermal process canning work relates the temperatures in the jars to the temperature inside the canner throughout the processing. No USDA thermal process work has been done with jars inside an electric pressure cooker, tracking the actual temperatures inside the jars throughout the process.  It is ultimately the temperature and heat distribution inside the jars that matters for the destruction of microorganism in the food product. The position of jars in the canner and flow of steam around them also impacts the temperature in the jars.  For example, there would be expected differences in jars piled together on their sides from those standing upright on the canner base.

2.  What matters is temperature, not pressure.  One manufacturer says its cooker reaches the pressure required for canning, but that alone does not prove the food in the jars is heated throughout at the same rate as in the canner used for process development. A manufacturer should do process development work to document temperatures throughout the unit at a given pressure and throughout the whole process time.  Just producing an interior pressure is not sufficient data for canning recommendations. For example, if air is mixed in the steam, the temperature is lower than the same pressure of pure steam.   That’s why a proper venting process is so important in pressure canning – to obtain a pure steam environment inside the canner. Also, one has to know how to make adjustments in pressure readings at higher elevations.  The same pressure and process time combination cannot be used at all elevations.

3.  In order to ensure the safety of the final product, the temperature in the canner must stay at minimum throughout the process time. Do power surges or drops with an electric canner cause the temperature to drop too low?  How will you the user know if that happens with your cooker?

4.  One of the big concerns is that the USDA low-acid pressure process times rely on a combination of heat from the time the canner is coming to pressure, during the actual process time, and then during the early stages of cooling the canner and jars.  Even after the heat is turned off under the canner, at the end of the recommended process time, the food remains at high enough temperatures for another period of time that can still contribute to killing of bacteria. This retained heat while the canner has to cool naturally to 0 pounds pressure before opening is used to advantage in calculating the total sterilizing value of the process to preserve some food quality. If anything is done to shorten the cooling period, including using a very small cooker, then the food could cool down more quickly, and be under-processed.  (That is why we recommend using only pressure cookers that hold four or more quart-size jars.) Bacteria are not killed in the food only during the process time; the time it takes the canner to come up to pressure, the process time, and the cool-down time all matter.  There is no way at this point in time to know exactly the percentage of contribution from cooling for each of the canning recommendations.

Please note: This statement about electric cookers does NOT include the Ball Automatic Home Canner for acid foods only, which is electric, but (1) is not a "multi-cooker", but a dedicated canner, (2) comes with its own instructions and pre-set canning options for specific food preparations, and (3) has had proper thermal process development done to support the recommendations with it. Jarden Home Brands also sells an electric boiling water canner, but it is not a pressurized appliance and for canning purposes operates similar to a traditional boiling water canner.  Directions from the manufacturer for this Ball canner, as well as for the Weck non-pressurized electric boiling water canners, should be followed to get them assembled and for managing temperature settings to achieve a boiling process.

For more information about canning in pressure cookers, please read NewsFlash: Canning in Pressure Cookers.

February 1, 2019
National Center for Home Food Preservation

Newsflash

Canning Homemade Soups

Can I can my favorite soup recipe at home?

Canning soup at home is an excellent way to preserve your vegetables with or without small portions of meats or seafood. The key to canning a safe, high quality soup is to follow directions provided by a reliable science-based source like USDA or partners in the Cooperative Extension System. 

Vegetable-based soups are usually mixtures of low-acid ingredients and they need to be pressure canned by a process that has been developed by research methods known to control for botulism food poisoning; we will not recommend any way to can vegetable or vegetable-meat soups in a boiling water canner.  Botulism is a potentially fatal foodborne disease.  Spores of the organism (Clostridium botulinum) that causes botulism can survive normal cooking temperatures and times.  The extra heat in pressure canning is needed to actually destroy the spores so when the closed jar sits at room temperature in storage, the spores will not grow out to cells that then produce the deadly botulinal toxin. The conditions in the sealed jar at room temperature are favorable for this organism to cause problems (moist, low in acid with a pH above 4.6 and very low in oxygen). 

There is only one version of pressure canning directions for home canned soups available from USDA and on this website.  Consumers should follow these directions exactly. If additional ingredients or thickening is desired, the soup should be canned as described and those variations should be made when the jar is opened for serving.

The USDA procedure is not an exact recipe; it allows you to have some choice of vegetables, dried beans or peas, meat, poultry, or seafood. It does NOT allow you to include noodles or other pasta, rice, flour, cream, milk or other thickening or dairy ingredients. 

If dried beans or peas are used, they must first be fully rehydrated (for each cup of dried beans or peas add 3 cups of water,  boil 2 minutes, remove from heat, soak 1 hour, heat to boiling, drain).   

Each vegetable should be selected, washed, prepared and cooked as you would for canning a ‘hot pack’ according to USDA or NCHFP directions. If there is not a separate canning recommendation for a vegetable, do not include it.  

Meats recommended for canning should be covered with water and cooked until tender, then cooled and the bones removed.  Next, all the prepared ingredients should be cooked together with hot water, broth or tomatoes, to boiling, and boiled for 5 minutes. Salt can be added to taste, if desired. Do not fully cook the soup before filling jars; the canning process completes the cooking at the same time it eliminates harmful microorganisms. 

A very important step in these procedures is that jars should only be filled halfway with the mixture of solids.  The rest of the jar is filled with the hot liquid leaving 1-inch headspace. 

Process the jars in a pressure canner according to instructions in the table relevant to your elevation, pressure canner type and jar size.

Slightly revised May 1, 2019
National Center for Home Food Preservation

Newsflash

Using Atmospheric Steam Canners

Can acid foods be processed in steam canners?

The University of Wisconsin, under the leadership of Dr. Barbara Ingham, has conducted research on appropriate use of atmospheric steam canners for home canning in collaboration with the National Center for Home Food Preservation (NCHFP).  Atmospheric steam canners are used for processing naturally acid or properly acidified foods with natural or equilibrated pH values of 4.6 or below. They are not pressurized vessels used for processing for low-acid foods. 

Sufficient studies and peer review have been completed that we are now able to say that as long as certain critical controls at various steps in the canning process are achieved, USDA and NCHFP process times for canning acid or properly acidified foods (pH of 4.6 or below) at home with properly research based recipes and procedures can be used. The research looked at temperature distribution in the steam environment surrounding the jars in a dome-style steam canner, heating patterns of several different food types during processing in the canner, and the contribution of standardized cooling procedures at the end of the process time.

Some of the key controls in addition to the acidity of the food product are knowing that the canner has had the air vented out of the steam before processing begins, and that the pure steam is at the temperature of boiling water at the start and during processing.  Jars must be preheated before filling with food and cooling prior to processing must be minimized.  Processing times must be adjusted for elevation, and must also be 45 minutes or less, including any elevation modification.  The processing time is limited by the amount of water the canner base will hold, and the canner cannot be opened to add water or for any reason at any time during the process.  Finally, cooling of jars must take place in still, ambient air without any forced, more rapid cooling. The slow cooling of processed jars is important to the overall food safety of the whole canning procedure.

Dr. Ingham provides further instructions and details about carrying out canning in an atmospheric steam canner using USDA acid food processing recommendations.

Please also see this update.

The results of this research were published in a peer-reviewed scientific journal in May 2015.
Willmore, P, Etzel, M, Andress, E. and Ingham, B. (2015). Home processing of acid foods in atmospheric steam and boiling water canners. Food Protection Trends, Vol 35, No. 3 (May-June), p.150–160.

August 24, 2020
National Center for Home Food Preservation

Newsflash

Acidifying Tomatoes When Canning

Why do I have to add acid when canning tomatoes in the pressure canner?

Tomatoes that are acidified for canning are done so to prevent botulism poisoning and other bacterial concerns by a combination of acid and heat; the control in vegetables, meat and other naturally low-acid foods is by heat alone.

The bacteria that cause botulism poisoning can grow and produce toxin in sealed jars of moist food at room temperature if the pH (measure of acidity) is above 4.6.  Vegetables, meat, fish, etc. are naturally fairly high above pH 4.6 (close to 6.0) and so pressure processes were developed for those to kill the heat-resistant spores of C. botulinum bacteria that are likely to be contaminating them.

Tomatoes also can have a natural pH above 4.6 (at least up to 4.8).  But rather than develop a pressure-only process as if they were all low-acid, since they are so close to 4.6, USDA decided instead to recommend a small amount of acid be added so they can be treated as a food with a pH less than 4.6 for home canning.  Therefore they are suitable for boiling water canning when the acid is added.  (The commercial industry often also adds citric acid to tomatoes to be able to give them a less severe heat treatment than would be needed for botulism and other bacterial controls.)

When you see the tomato product recommendations in USDA canning directions that offer both boiling water and pressure canning options, those pressure processes are still only the same amount of heat treatment as the boiling water option.  (Higher temperature=shorter process time.)  Those pressure processes are not the amount of heat and time that would be required for canning a low-acid food to control for botulism.  There has not been a properly researched process for pressure canning of low-acid tomatoes without added acid, so the available process times still require the addition of acid as if they are being processed in boiling water.

Another example of how an acid food has both a boiling water and pressure process available is canned peaches.  Peaches (in pint jars) can be canned for 20 minutes in boiling water or 10 minutes at 5 pounds pressure in weighted gauge canner.  That pressure process is not a botulism control either, just because it is pressure canning.  The two time-temperature combinations are the equivalent amount of heating with regard to killing bacteria.

There are some tomato products in the USDA canning procedures that only have a pressure process listed (for example, tomatoes with okra or zucchini, spaghetti sauces, Mexican tomato sauce, etc.).  If a pressure process is the only listed option, then it is the required processing method and we do not have a boiling water process option available. These products made according to the stated recipes and procedures are low-acid food mixtures.

September 4, 2013
National Center for Home Food Preservation