Commercial sterilization of canned goods is done at 15 pounds pressure / 250 F [103 kPa / 121 C], which consequently requires a far shorter period of processing time. We can achieve 15 pounds pressure in our home pressure canners, but all home processing recommendations start at a sea level base of 10 pounds pressure / 240 F [69 kPa / 115 C], which requires a longer period of time.
Why not higher processing temperatures for home?
You may wonder why then there aren’t home-use recommendations for the higher pressure / shorter time. The answer might be simply: the research for our home processing times was done at 10 pounds pressure, and funding would be needed for the research to redo the times for each item the USDA currently has 10 lb times for.
In a 1983 survey of the history of home canning thus far, Dr Elizabeth Andress wrote:
A few recommendations have been made over the years for home canning of meats at 250F / 15 psig [ [121 C / 103 kPa] (Cover et al, 1943). It was later found to be unnecessary, but the higher temperature was and is used successfully, especially with commercial products.
At present, 240F / 10 psig [115 C / 69 kPa] is the most commonly recommended temperature. More recent interest in conserving nutritional and textural characteristics in canned food has led to some research with higher pressure (temperature) and shorter time processes.
Use of 250F [121 C] in home canning has been limited due to a lack of research at this temperature. Shorter process times would be required at 250F [121 C], as lethality accumulates about three times faster than at 240F [115 C] (Zottola et al, 1978). These authors and Nordisen et al (1978) recently investigated heat penetration rates for low acid foods processed at 15 psig [103 kPa.] Convection-heated foods required about one-third the time as specified for processes at 10 psig [69 kPa.] Those foods heated by conducting or a mixed mechanism appeared to require equal time at 10 and 15 psig [69 kPa and 103 kPa.] It was concluded that each product be investigated before recommendations could be made.” [1] Steam Canning. In: Andress, Elizabeth L and Gerald Kuhn. Critical Review of Home Preservation Literature and Current Research. Athens, GA: University of Georgia, Cooperative Extension Service. 1983. https://nchfp.uga.edu/publications/usda/review/equip.htm#psig
Note that though some jarred products sterilized faster at 15 lbs, some sterilized at the same rate as 10 lbs — so research would need to be done to determine which was which. And, what about people whose altitude already requires 15 lbs as a base?
In 1986, Nancy Hudson, a former extension agent in Greene County, Ohio, explained the reason for the recommendation as given to her by Dr Gerald Kuhn, who pioneered the first USDA Complete Guide. She cited the reason of too-short processing times for some items:
As of 1987, USDA will no longer recommend 15 lbs. pressure. Part of the problem is when 15 lb. pressure is used and zero or one minute processing, there is not sufficient time for all of the air to vent out of the canner and for the internal canner temperature to raise. Using 15 lb. pressure at zero or one minute processing will increase spoilage.” [2] Hudson, Nancy. New research gives tips on using jars and lids. Xenia, Ohio: Daily Gazette. 7 April 1986. Page 6.
All of which is to say: in case you’ve wondered, there’s the current reasons. If you want it changed for products that can support 15 lbs processing, tell your elected representatives you’d like some money invested in researching this!
10 pounds pressure is higher than it seems
For the record, our 10 lbs pressure is actually slightly higher than that.
A pressure of 10.5 pounds at 0 to 1,000 feet of altitude is required to reach 240 F [115 C] degrees inside the canner… The pounds of pressure figure was rounded to 11 pounds in dial gauge canners to avoid the confusion of half-pound recommendations. Weighted gauge canners are already machined to operate at 10.5 pounds as a built-in safety factor when they are set at 10 pounds.” [3] Patrick, Ruth M. Canning Green Beans. Revised November 2009. Louisiana State University Agricultural Center. Accessed March 2015 at https://www.lsuagcenter.com/MCMS/RelatedFiles/%7BB9014A9B-CD62-4F8F-92AE-FF60503C43A8%7D/CanningGreenBeans.pdf
That doesn’t change processing times or pressures one iota, but there you go, just some poundage trivia for your next canning party!
Are there any exceptions to the 10 lbs at sea level norm?
There appears to be a small handful of exceptions in the USDA 2015 Complete Guide, for which 15 lb at sea level processing directions are given for weighted-gauge canners. This includes Tomato Juice (page 3-5), Tomato and Vegetable Juice Blend (3-6), Crushed Tomatoes (3-7), Standard Tomato Sauce (3-8), Tomatoes Whole or Halved (3-9 to 3-12)
Provision for 15 lb processing at sea level for crushed tomatoes (USDA Complete Guide 2015. Page 3-7. Note: no provision for higher pressures above 1000 feet / 300 metres.
Look at the incredible time difference when pressure canning whole tomatoes at 15 lbs:
Only 1 minute for whole tomatoes in water at 15 lbs pressure. (USDA Complete 2015, page 3-10)
What heats does pressure canning achieve?
Tanner, F.W. and Grace B. Armstrong. Canning Fruits and Vegetables. Circular 614. Urbana, Illinois: University of Illinois Extension Service. June 1947. Page 6.
References
Angell
Hi I have pressure canner it will only get up to 8#s of pressure can I still use to process my foods? And process longer?
Rosalie Stewart
Hi! I accidentally canned my food at 10 lbs but realized after the fact that we should have used 15 lbs because we live at 3000 feet. Everything is sealed, but will it be OK?
Healthy Canning
The food is underprocessed. I can’t tell you it will be okay. You may wish to speak with this group of Master Food Preservers to decide how to proceed: https://www.facebook.com/UCCEElDoradoMFP/
Janis McLendon
I accidentally pressure canned green beans in quart jars for 3 minutes instead of 25 minutes. I read the wrong chart in canner booklet. Will.they be safe of can I repressure them???
Lauren
I live in Spokane, Washington. I want to pressure can meats. What weight am I to use?
Healthy Canning
Here is the guide to adjusting pressure for your local altitude: https://www.healthycanning.com/altitude-adjustments-for-pressure-canning/
Margo Gonzalez
I have a pressure canner that works well, but every time I use it and it gets to the point to put the weight on it gets harder for me to regulate. I mean it goes a little over 10 pounds when it starts to shake. Lowering my fire does not seem to help. Will my jars be okay?
Heather
Hello
I live at 1,058 ft above sea level. I used 10lb weight to process my soup. Will that be ok or should I use 15lb weight?
Thanks
Healthy Canning
The 10 lb is fine. If you lived at exactly 1000 feet above sea level, but on the 6th floor of an apartment tower, I’m pretty sure you would still be classed as 1000 feet.
blanche
I live at just under 4000′ and do my canning in the outdoor kitchen on a camp stove. The lowest flame in summer heat keeps the pot at a steady 15 lbs. Am likely to harm my foods running that high for full USDA times? Mostly canning meat based products. Very little vegetables included.
Kathy Gassen
Where can I get a 10 pound pressure regulator. Mine only has 15. None of recipies call for15 only 10. It is a presto. Will it work changing it to a 10from a 15pp?
Healthy Canning
Please see here for a discussion of Presto pressure canner accessories.
Shirley
I just realized today that I have been canning using a 15lb weight instead of 10lb. I have canned meat, green beans, potatoes, squash, and soups. Do I have to worry about spoilage if they have all sealed!!?
Healthy Canning
They will be overprocessed, so the food might be a little bit softer than it would otherwise, but the jars will be safe.
Susie
I live at a level of 1310 and I have always canned with 10#. I have never had problems with spoilage or failed Jays. I took a break from canning to caregive for my parents and when I started back up I was questioned about my canning weight. I decided I would go ahead and try the 15# weight as recommended and I have not had good success. Am I that far above the thousand to have to go to 15 pounds? I don’t know if I’m in a dip here on our property or what but 15 pounds at the same length of time as the 10 pounds is cremating my food.
Rebecca
Go to Presto web page, Amazon, or http://www.pressurecooker-outlet.com
Bernard john hayes
All I have is a 15lb weight can I still can at the 10lb time limit
Healthy Canning
You need to get a 10 lb weight to avoid overprocessing your food and ending up with unpalatable results.
Billy Reed
I am looking for a modern guide to pressure and retort canning at higher pressures 15lb + any direction would be helpful.
Thanks
Healthy Canning
Such guides would exist commercially. I myself wouldn’t be familiar with such sources; try asking Dave French at https://www.aardvarkassoc.com/
Jean
I want to pressure can pints of yellow wax beans in my every-day, Fagor pressure cooker. My pressure settings are low at 215 degrees or high at 250 (15 psi). All of the canning recipes I see say to use 10 lbs of pressure which is 240 degrees, which is not an option on this pressure cooker. Is it alright to use the 15 lb setting for the recommended 20 minute time stated for 10 lbs?
Healthy Canning
Sorry, we don’t have any recommendations for doing pressure canning in a pressure cooker of whatever brand. Freezing would be a good option for yellow beans. Here are directions for freezing: https://nchfp.uga.edu/how/freeze/bean_green.html