It’s important to follow the proper cool down process after water bathing, and steam canner processing, for both the safety, and quality, of your home water bath and steam canner processed products.
Here is the cool down procedure:
- When the water bath processing / steam canning time is up, turn off the heat, and remove the canner lid;
- Leave the jars as they are in the canner;
- Set a timer for 5 minutes;
- At the end of 5 minutes, remove the jars and place them on a towel or a wire rack somewhere away from cold drafts;
- Do not cover jars; do not touch rings (unless you are using Tattler lids);
- Let jars sit untouched for 12 to 24 hours.
Don’t cover the jars in an attempt to lengthen the time that the jars stay warm — you run the risk of your jars developing flat sour.
Just let the jars cool naturally out on a counter or table, away from drafts or cool breezes.
After the time is up on the recommended hot water bath processing time for your recipe, turn off the heat, remove the cover, and let the jars settle for 5 minutes  This settling is for product quality: it helps prevent an extremely fast change in temperature for the jars, causing contents to surge up onto the rims causing sealure failures. Have a wire rack or thick hand-towel placed out somewhere free of drafts or cool winds. After the 5 minutes, remove the jars and place on your prepared surface at least 3 cm (an inch) apart. Placing jars apart helps keep the jars out of moderate temperature zones where flat sour could develop. Don’t cover the jars with a towel or anything. Covering the jars could also keep them in moderate temperature zones. Let stand for 12 to 24 hours undisturbed Lids actually may seal and unseal several times during this time, so let them do their thing., then remove rings, check seals, wash jars if needed, label, and store away without the rings on.
Researchers found that the cool-down period was actually an important part of the sterlization
In 2014, researchers in the Department of Food Science at the University of Wisconsin-Madison tested home preserving three foods (applesauce, tomato juice, and cranberries) using the boiling-water bath method. The study was published in January 2015 in Food Science & Nutrition journal.
They followed the USDA Complete Guide (2009) research-based methods and processes, processing the jars in a boiling water bath canner for the recommended periods of time. Among their other findings, they found that the USDA recommended cool-down procedure for the jars after hot water bath processing was actually a critical part of the process. A lot of bacteria inside the jar are still being killed while the jars are cooling down from the high heat of the boiling water.
So, when you are water bath or steam canning,
Don’t lose your cool!
What the researchers said
Here are some extracts from that January 2015 Food Science & Nutrition article:
Most of the lethality during home canning occurred during air cooling, making cooling of home canned foods of great importance.
“We processed applesauce, tomato juice, and cranberries in pint jars in a boiling water canner to test thermal processing theories against home canning of high-acid foods. For each product, thermocouples were placed at various heights in the jar. …. There was a cold spot in the jar, but the cold spot during heating became the hot spot during cooling. During heating, the geometric center was the last to heat, and remained coldest the longest, but during cooling, it was also the last to cool, and remained hottest the longest. … Most of the lethality during home canning occurred during air cooling, making cooling of home canned foods of great importance.”
“The cold spot during heating becomes the hot spot during cooling.”
“Thus, as long as up-to-date, research-tested home-canning [Ed: water-bath] practices are followed for high-acid foods [Ed: most jams, jellies, pickles and relishes], consumers can be reassured by the inherent safety of the product that they are producing for themselves and their families.”
Etzel, M. R., Willmore, P. and Ingham, Barbara. H. (2014), Heat penetration and thermocouple location in home canning. Food Science & Nutrition. doi: 10.1002/fsn3.185. Accessed June 2016 at https://onlinelibrary.wiley.com/doi/10.1002/fsn3.185/full
|↑1||This settling is for product quality: it helps prevent an extremely fast change in temperature for the jars, causing contents to surge up onto the rims causing sealure failures.|
|↑2||Placing jars apart helps keep the jars out of moderate temperature zones where flat sour could develop.|
|↑3||Covering the jars could also keep them in moderate temperature zones.|
|↑4||Lids actually may seal and unseal several times during this time, so let them do their thing.|
Why did you have a photo of a pressure gauge, not a water bath canner? And is the cooling down phase the same for a steam canner?
That’s a photo of an analogue clock app on an Apple iPad. For steam canner cooling, see here: https://www.healthycanning.com/steam-canning#Steam_canning_processing_steps
Could you explain the science behind the 12 to 24 hour cooling period please. I cannot find this information anywhere. Why 12 to 24 hours, why not 4 or 6 or 8? If the jar is completely cool all the way through 6 hours after canning then I don’t see the purpose and not touching it for another 6 hours. But I would really like to know the science behind this.
Help! Hello last night I accidentally left my quart jars of tomatoes in the water bath for 4 1/2 hours after I turned off the heat. Are these still safe? Thank you!
yes but it may not taste good
One of the reasons you want to get them out right away after processing is that you run the risk of flat sour. https://www.healthycanning.com/flat-sour/
Hello! I just canned some corn relish this afternoon and accidentally left a batch in the hot water bath after processing. It was in the water for about an hour and a half while I went to get my son from school. All of the jars seem to be sealed but I was worried that sitting in the water for too long might pose a problem. Do I need to be concerned or are these ok to keep in the pantry? Thanks!
hi i dropped one jar several times trying to remove it from the canner with regular tongs. Can I trust the seal? Should I assume that food hit the rim and it won’t be able to seal now?
If it seals, you are good to go.
I want to can some peach preserves and I have a small rack that handles the smaller jars. I can process four jars at once but my recipe will yield six jars. Can I process them sequentially or should I use a bigger rack and water bath?
I am finding it difficult during this pandemic to purchase what I actually need so I am trying to make due with what’s available. Do you have a resource page that has supplies?
You can waterbath process them 4 jars at a time. A resource page is likely a good idea; added to todo list!
Some of my 1/2 pint jars did not seal. I could lift the lid off easily. I placed them in the fridge overnight and I can no longer lift the lids. Can I use they are safe and can now leave them in my pantry?
No, they will not be safe unless reprocessed. Very frustrating when this happens.
Thanks for your responses it is a lesson learned as I am a beginner so it is all part of the learning process. 🙂
I hope you found an answer already but I wouldn’t consider that to be safe!
Hi! I am just now seeing your post. I have found each time I put an unsealed jar into my fridge, like yours, it seems to seal up after awhile. However, bringing the jar out of the fridge to room temperature, like at breakfast table to use, the lid pops back up in a short time. So, it is simply making a false seal from the cool fridge environment.
I put my jellies into the fridge immediately if they don’t seal, so I have no problem using them by storing in my fridge. They never go to the pantry, unsealed.