Tuesday, May 3, 2011

More canning info

On my Canning Mustard post, a reader named Dannie asked a very good question. She wrote:

I just purchased my first water bath canner and my daughter and I plan to do canning together this summer. Being new at this I just wondered if you could tell me why you had to heat the mustard before you put it in the glass jars. It seems like double cooking to me but I know there is a logical reason.

I realized I had no suitable answer to this question. I have raw-packed foods before (notably bacon) but most of the time I hot pack foods. But why hot pack? I never gave it much thought. My favorite canning reference book, Putting Food By, mentions hot food packs better and requires less processing time. Somehow this didn't seem like the whole story.

So I turned to an expert named David Blackburn at a wonderful website called CanningUSA.com and posed the question. Here is his response:

In the case of mustard (and all canned products,) temperature control has to do with viscosity and kinetic energy. Basically, the thickness of a liquid, solid or gas, determines the combination of time and energy it takes to change its temperature. In canning, we are most concerned with the lowest core temperature.

The easiest example of this is canning whole tomatoes, which are not viscous. If you cold pack them, they need to be processed in pint jars for 85 minutes in a water bath canner. If you hot pack them, it's 40 minutes. The former cooks at the temperature of the waterbath canner, or the boiling point of water - 212 degrees at sea level, after it's brought both the water in the canner and glass jars up to temperature. The latter process heats the tomatoes using a wood, electric or gas heat source before canning. Depending on the energy source, this temperature is nine to fifteen times higher than the boiling point of water. So, it's a lot faster and more energy efficient to heat the product up to its boiling point first, can it and then process in the canner. When there is an option between the two processes, I only publish the least in overall time and energy consumption.

Let's go back to your mustard question. Imagine heating a pint of water and a pint of mustard on a stove top. For the water, you can put it in a pan on any heat source and at any temperature and it pretty much takes care of itself. You don't have to worry about it burning or heating unevenly because it has a low viscosity. For mustard, which is much more viscous, so you have to heat it more slowly and stir it constantly to make it heat evenly and to ensure it doesn't stick or burn. I haven't calculated it, but you could sumise it takes more energy and time to heat mustard than water. If you placed the mustard in a jar inside a waterbath canner, it would take an eternity for its lowest core temperature to reach the appropriate canning processing temperature. As far as your bacon is concerned, it isn't viscous and the paper doesn't impede the processing.

I also noted a question on your post about electric tops and pressure canners. Electric heat sources do not heat evenly, so you can't control the temperature. The glass tops are not flat, which makes it worse. We recommend buying a small gas burner and external tank, such as propane, which burns a lot hotter than natural gas.

Wow, I think you'll agree that Mr. Blackburn's reply is a lot more intelligent than anything I could ever dream up! I'm grateful he took the time to explain the process.

Thanks, Dannie, for asking such an excellent question.


  1. I have encountered a situation that Mr. Blackburn did not address about glass yop stoves. Thankfully, we discovered this by a warning - perhaps in "Countryside" - and not by experience.

    Glass yop stoves are not designed for the heat generated by pressure cookers, and there is a real danger of breaking the glass top. We have done ok with just the hot water baths for high-acid foods, but we do not use our glass top stove for the pressure cooker.

  2. yes! i knew it was a good decision to go with propane gas cookstove and i have won the bet with my husband! thank you patrice and mr. blackburn.

  3. Terrific info! I also wondered about the cold-pack vs. hot-pack differences. Why some and not others.... Great answer.

    By the way, I noticed in one of your canning photos that you add water to your beef chunks before canning. My canning DVD teaches to simply dry-raw-pack the beef chunks with the appropriate amount of salt and some pepper. Have you ever noticed a difference? Is one method better than the other as far as the finished product turns out? My beef tastes fantastic out of the jar so I was wondering if adding water prior to canning would make it more watery? Or just more juicy? The raw-pack beef method is quick and easy but it actually 'cooks' right to the inside of the canning jar so I need to scrub to get it clean and I was curious about the addition of water. Your thoughts and experience are much appreciated.

    God Bless,
    Janet in MA

  4. My husband purchased a Rocky Mountain Range from Cabelas. We use it outside to do all our canning. It's much quicker that the electric stove, and keeps the heat out of the house!

  5. In short, you heat the food and pack it hot to make sure it gets HOT ENOUGH in the center. The outside is easy to get heated. You want the center heated to the temp that kills the bad germs. It takes less time if you start hot.

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    Not sure if I have this in the right place but if not maybe ou can place where it will be noticed.
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