From the Helpline

We receive food preservation and food safety questions from all over the world. What follows are some of the most popular and intriguing ones.  Remember, if you have a question for us, please use our contact form:  Got A Question?.  We would love to help you safely preserve!

Steam canning, or atmospheric steam canning, can be a safe method for home

From the National Center for Home Food Preservation: 

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:  read more

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 altitude, and must also be 45 minutes or less, including any altitude 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 at her webpage:  http://fyi.uwex.edu/safepreserving/2015/06/24/safe-preserving-using-an-atmospheric-steam-canner/ .

Eventually we will integrate this more complete advice into additional offerings on the National Center for Home Food Preservation website.

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.

September 9, 2015
National Center for Home Food Preservation

I reside in San Diego. I believe you are the closest facility to perform the annual testing on my Presto canner pressure gauge. You advertise that you can do the testing at your facility in Orange County during a public event.  As there are no public events at which to have this service done due to Covid19 - has an alternative procedure (mailed in perhaps?) been developed?

Presto will test canner pressure gauges for free, but they must be mailed in.  See details in a previous Helpline request below.  As an alternative, you can buy a weighted gauge regulator for your Presto so you don't need to rely on the dial. You would also be able to get an idea of the accuracy of the dial by comparing it’s reading when the weighted gauge started to regulate the pressure. 

Per Presto: 

Presto makes a 3-piece adjustable weight that can “convert” your Presto Gauge Pressure Canner into a dual-gauge pressure canner, like the All-American. It's a 3-piece weight that adjusts easily to 5, 10 and 15 lbs of pressure; the Presto part number is 50332. This 3-piece weight is only designed for use with a Presto. 

This item is available at several locations/internet sites by googling "Presto weighted gauge pressure canner" or similar. 

Here is a YouTube on how to use a weighted gauge pressure canner, not for Presto, but similar product:

https://www.youtube.com/watch?v=uAUC6cvpW0Q

And, in case you need the canner manual:

https://www.gopresto.com/content/parts-service/manuals-finder

Pressure canners with only a dial gauge need to be tested annually to ensure dial gauges are accurate.  If your dial gauge is not accurate, it is not correctly reading pressure which may result in under or over processing and unsafe food.

UCCE Master Food Preservers of Orange County recently acquired a device to test Presto Brand pressure canner gauges and offer free pressure gauge testing at our public workshops and events scheduled at the South Coast Research & Extension Center.

For a listing of our workshops and events, please check our website Home Page calendar regularly.

See information below for the two major pressure canner companies: All American and Presto. 

All American Pressure Canners:  If you have an All American pressure canner, All American, as well as its parent company, Wisconsin Aluminum Foundry, does not provide this service.  A telephone conversation with a service representative at All American revealed that the cost of mailing the old parts for testing was more than the cost of replacing the part(s). In fact, if you have a model older than 1995, you can simply replace the older gauge with a newer one. 

Presto Pressure Canners:  Presto will test Presto canners for no charge. Simply send gauge to them (prefer shipment by UPS; allow turn around time of more than two weeks, so plan ahead!)

NATIONAL PRESTO INDUSTRIES, INC.
Consumer Services Department
3925 N. Hastings Way
Eau Claire, WI 54703-2209
Phone: 1-800-877-0441 1 – 800-368-2194.
Email: contact@gopresto.com

Information on purchasing your own Presto pressure testing unit is at the National Center for Home Preservation’s site: http://nchfp.uga.edu/educators/Presto%20Testing%20Unit%20ADW07-5239C.pdf

General information:

An excellent article on pressure canners, which includes discussion about the weighted gauges and dial gauges, as well as resources for testing the gauges can be found at: 
http://ucfoodsafety.ucdavis.edu/files/75897.pdf.

This publication also shows other parts of the state where gauges can be tested, such as

Non-UC Testing Services:
Embarcadero Home Cannery
2026 Livingston Street
Oakland, CA 94606
Phone: 510-535-2311
Email: ehcan@hotmail.com
Dial gauges are tested for approximately $5 plus return postage. Individuals would remove the gauge and mail it to EHC. They will test it using their master gauge and return it with a report as to its accuracy and invoice. They sell new gauges for $21. Once mailed, EHC will return within a week.