Safe home canning is all about killing illness-causing microorganisms.
Gosh, I hope that you have listened to or read the show notes for the podcast on mistakes to avoid in home canning because it's important one! Why? Because there is so much information out there is just isn't that fantastic or potentially unsafe. But, don't rely on me, always double check reliable sources!
Before we get into air cooling, let's back up for a moment and quickly touch on the research that is done to test canning procedures and canning recipes. Thank you food scientists!
- Experimental processes and procedures are designed to to ensure factors such heat penetration, heat transfer, thermal lethality, and canner safety are tested and evaluated.
- Testing equipment such as thermocouples are used to measure temperatures at prescribed intervals to determine the heating pattern of the canner. The theoretical cool spot of the food in jars is determined and monitored. The rate heating and cooling of the food in the jars are recorded and evaluated.
What is air cooling?
Air cooling is the time after the jars are removed from the canner, placed on a protected surface away from drafts, and allowed to cool for 12-24 hours.
What is not air cooling?
Air cooling doesn't include freezing, refrigeration, ice, cold water, snow, freezing outside temperatures, or any strategy to accelerate the rate of cooling. Just don't!
Why is air cooling so important?
Air cooling is the critical time after the jars are removed from the canner during which the majority of lethality (killing of illness-causing microorganisms) occurs!
Yes. In fact, one recent study determined that in the case of apple sauce that 90% of lethality occurs in the cooling stage and for tomato juice 60% of lethality occurs during the cooling stage.
During cooling mostly convection heat transfer is taking place. What?! The heat transfer happening inside the jar is faster than the transfer of heat to the surrounding air.
What the hell does that mean? That means that the heat transfer continues until the the jars have cooled--creating a wonderful, safe, shelf stable home canned food.
The safe preservation of food by canning requires and includes air cooling. Don't attempt to expedite the cooling of home canned food!
Be safe as you are proceeding at your own risk. Be safe and eat well!
Etzel, M.R., P. Wilmore, and B.H. Ingham. 2014. Heat penetration and thermocouple location in home canning. Food Sci. Nutr. (accepted October 10, 2014). Published online December 9, 2014: http://onlinelibrary.wiley.com/doi/10.1002/fsn3.185/full.
- Kansas State Research and Extension, Preserve it Fresh, Preserve it Safe.
- University of Wisconsin-Extension, Safe and Healthy: Preserving Food at Home
- USDA, National Center for Home Food Preservation, Complete Guide to Home Canning (2009 version)
- Utah State University Extension, Food Preservation Fact Sheets