I've been pressure canning zucchini soup the past 2 years and it's a beautiful thing. This year I used a different pressure cooker, and I've just found out that 15psi on this pressure cooker is actually more like 13psi, and the internal temperature gets to 235 maximum when it says 15psi.

Well, that means that I didn't meet the rules of 240-250 degrees for 15 minutes and I have 20 cans of soup to show for it. I also learned while researching that it may not be a good idea to puree the soup before canning due to high viscosity and heat distribution, and it is indeed pureed, so I have two issues to combat. All of the can seals are still in tact, but it's only been a few weeks.

I've come up with a few options:

  1. Re-can the soup. Just put new lids on, bring the water up to boiling for a minute or two before putting the lid on and building pressure. This will help with heat distribution from room temp up to boiling point since this is not freshly cooked and hot soup. I will also keep the water level in the pressure cooker to just below the fill level in the bottles to further combat the viscosity/heat distribution issue with the puree.

  2. Sterilize then freeze the soup. Pour the cans from matching batches right into the pressure cooker, bring it up to pressure to kill anything that may have formed, then bring down to about room temperature inside of sealed pressure cooker, pour into containers and freeze it. This method addresses my fear of the pureed/viscosity issue.

  3. Refrigerate, use ASAP.

  4. Put the cans in the freezer.

  5. Leave it alone. Is 235 degrees good enough? Are those extra 10 degrees important? Is everyone else in the world as precise as me, or was there a safety factor when they came up with those numbers?

I'm not sure which is the safest option. All I know is I dodged a major bullet by finding this out early. In the future I will can the soup before pureeing as well.

  • 3
    What I did was leave the food canned in the jars on the shelf, none of the seals broke. I took the soup out in batches of 4 cans at a time and pressure cooked them at a real 15psi for 45 minutes, which is overkill to kill botulism if any even was in the soup, if any even survived canning. Surprisingly, the quality of the soup didn't suffer too much. Nobody died. Jan 19, 2018 at 14:28

2 Answers 2


I personally to be on the safe side would freeze it in another container. To freeze it inside the jars you would have to make sure you left enough room for expansion, which all foods to when frozen. If you didn't leave enough room to freeze in the jar, I would worry the lid would pop-off. That is why I feel your best bet would be freezing them in another container, leaving room for expansion.

The pressure cooker has the ability to sterilize, but it takes time. Clinical sterilization can only be achieved by running a pressure cooker that reaches 15 PSI at high pressure for 30 minutes – pressure cookers that do not reach 15 PSI, like most electric models, will require even more time.

Few pressure cooker recipes actually need 30 minutes of cooking time. Pressure cooking food for less than 30 minutes is not going to kill any more bacteria than bringing food to a boil (212F/100C). However, just like boiling without pressure, bringing a cooker to pressure will kill most bacteria responsible for cases of food poisoning like, Salmonella6, Campylobacter7, Lysteria8 and E.Coli9.

Read more: 3 pressure cooker nutrition myths that just won’t go away… ’till now http://www.hippressurecooking.com/3-pressure-cooker-nutrition-myths-that-just-wont-go-away-till-now/

I found this on Pressure cooking for Dummies: http://www.dummies.com/how-to/content/pressure-cookers-for-dummies-cheat-sheet.html

Temperature-Pressure Ratios for Pressure Cooking The following table translates the pressure setting on your pressure cooker to temperatures and pressure levels:

Pressure Setting Cooking Temperature Pressure Level in Pounds per Square Inch (psi) High pressure 250 degrees 13–15 psi Medium pressure 235 degrees 10 psi Low pressure 220 degrees 3 psi

Should you try the freezing method, make sure you get as much air out of the container as possible to minimize ice crystal formations at the top, and freezer burn. I bet you can use the puree to make some great recipes over the winter, even bread depending on the kind of spices you added.
Good luck


Seeing as canning is significantly different to pressure cooking, I'd say options 1,3,4, and 5 are somewhat sketchy and perhaps/probably unsafe. So either toss it out (better safe than sorry), or open the jars then boil the heck out of it (or pressure-cook it in the canner like you said) and freeze it (I'm hesitant to say this though as I dont want to be responsible for you getting sick if it doesnt work properly...).

The biggest concern with canning is the botulism toxin which I believe is tasteless and odorless and rather deadly and just loves the airless environment on the inside of sealed jars. The advised times for canning foods are always for the item with the longest processing time in the mix and take into account the density (as you have mentioned) to ensure that the heat has properly penetrated the food in the jar and thus killed off all the botulism spores that are present everywhere that would otherwise flourish in the airless environment.

Regarding increasing the water level in the canner... I would advise against that and to always just follow the manufacturer's directions... I've seen too many wrecked canners. Plus (and perhaps the bigger issue) is that adding more water might make it hard to get up to pressure as water is a liquid and thus has a different temperature-pressure curve to gas (steam).

I'm on a canning group on facebook that really advocates safe practices and the admins and the "canning gurus" on there only ever advocate tossing improperly canned goods after about 48 hours without refrigeration... it sucks but it does keep people safe.

There probably ARE tolerances in the safe canning guidelines, but without knowing exactly what they are and how much even normally and perfectly following the guidelines in a home kitchen pushes the tolerances due to the unavoidable inaccuracy in a home kitchen... Its not a good bet to assume its within tolerance and thus okay.

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