canning tomatoes

Asked October 22, 2018, 10:27 AM EDT

I purchased a box of canning tomatoes from the farmers market, skinned and cored them, cut them into pieces, crushed some of them (not all) with potato masher, added 4 teaspoons of citric acid powder to the mixture and stirred thoroughly, loaded 32oz canning jars, and placed them in my new pressure canner. I've canned in water bath but this was my first time pressure canning. I placed the 10 weight on and maintained 10 or 240 degrees for 30 mins. All but 1 popped. I removed the rings and can lift the jars holding the lids so they have a good seal. I did all this yesterday evening so around 10-12 hours ago. I noticed 2 things: 1) the level of the jars has dropped – in other words there is more space between the top and the lid than there was when I filled them; and 2) there appears to be foam in the jar. When I shake it the foam forms and then it settles, though it doesn’t seem to go away completely (see pictures). On the internet I’ve seen some posts that say throw it all away and others that say this is normal. Any advice would be appreciated.

Arlington County Virginia

3 Responses

Your description of the process sounds correct. Given that the headspace in the jar has changed from 1/2 inch to well over an inch and its less than 24 hours I would reprocess the tomatoes. You can find research based, validated recipes for canning in the USDA Guide to home canning. The tomato canning portion can be found here: Another resource is the National Center for Home Food Preservation at
Generally in tomatoes that were placed in a pressure canner with correct headspace and suffer this much liquid loss from the jar is a result of a sudden pressure change. If the weight was removed before the canner completely cooled and the pressure had dropped to zero, that sudden pressure change would result in a loss of liquid like you are seeing. As for the foam, I have seen tomatoes have that before and following proper canning methods is not a cause for concern. If you would like to discuss this further and would like to talk, I can be reached at 1-434-645-9315. When reprocessing you will need to follow all the steps in the recipe leading up to placing the jars in the canner and then follow the proper canner venting, bringing canner to pressure, processing times for selected method, and cooling. If you choose to water bath, the venting and pressure do not apply.

Thank you Eric - I did remove the weight when the canner was hot because I thought doing so would cool it more quickly and I could begin canning a second batch. I missed this detail from the instructions and didn't know this was would cause a problem. There was definitely a sudden pressure change as you pointed out that I now know caused my liquid loss. I will repeat the process and leave the weight on this time.

I am glad to help find the cause of liquid loss. It will take about an hour for the canner to cool down with no pressure left. Consult your canner manual on how to check to make sure the canner is cool enough to remove the weight. Usually, when you think the canner is cool, you would use a fork to gently rock the weight once to see if any pressure is left. If you do not get a hissing sound from steam escaping, you repeat the process to be sure. Then the weight is removed and wait about 5 minutes to make sure the pressure is stabilized before removing the lid. If the canner is a new one, it will have a safety lock feature with a indicator that the canner still is under pressure. The indicator is usually a piece of metal that raises up to initiate the safety lock when pressure is present. Please call the office or post if you have any additional questions or concerns.