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Canning: water-bath temperature and high altitude adjustments


operaflute
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Here's a question that has made me crazy for some time.

When canning/preserving using a hot water bath, often a temperature is given for the water bath rather than "full boil." (Ex - pickles are often done at a lower temp than a rolling boil - 185 deg F - to preserve crispness).  In the same breath, the directions will often say to increase the processing time for high altitude according to a chart.

My question: If I can get my water to waterever temp the recipe calls for, why do I need to increase the time for altitude.  Water boils at a lower temp at higher altitude, but 185 is 185 no matter what altitude, correct?

What am I missing?

Thanks!

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You're right that 185 is 185 no matter the altitude. If you can reach and maintain that desired temperature, then the time at that temperature should be the same if you're processing sealed vessels.

Nancy Smith, aka "Smithy"
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Processing times are inherently increased in low-temperature recipes that are tested safe but the use of an accurate thermometer and timer is essential.

 

 

In water-bath processed recipes where the boiling point is inherent, processing times must be increased because water boils at lower temperatures as altitude increases. Increasing the process time compensates for lower boiling temperatures. 

~Martin :)

I just don't want to look back and think "I could have eaten that."

Unsupervised, rebellious, radical agrarian experimenter, minimalist penny-pincher, and adventurous cook. Crotchety, cantankerous, terse curmudgeon, non-conformist, and contrarian who questions everything!

The best thing about a vegetable garden is all the meat you can hunt and trap out of it!

 

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Right, of course. Water boils at lower temps higher up. But many recipes state a water bath BELOW my boiling point. If I can achieve that temp, there should be no reason to compensate for my altitude, as far as I can tell.

 

Processing times are inherently increased in low-temperature recipes that are tested safe but the use of an accurate thermometer and timer is essential.

 

 

In water-bath processed recipes where the boiling point is inherent, processing times must be increased because water boils at lower temperatures as altitude increases. Increasing the process time compensates for lower boiling temperatures. 

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As I said above, the processing time has already been necessarily increased in safe 180º to 185º F recipes to compensate for the lower temperature so there's no need for further adjustments.

 

"Low-Temperature Pasteurization Treatment

The following treatment results in a better product texture but must be carefully managed to avoid possible spoilage. Place jars in a canner filled half way with warm (120º to 140º F) water. Then, add hot water to a level 1 inch above jars. Heat the water enough to maintain 180º to 185º F water temperature for 30 minutes. Check with a candy or jelly thermometer to be certain that the water temperature is at least 180ºF during the entire 30 minutes. Temperatures higher than 185ºF may cause unnecessary softening of pickles. Caution: Use only when recipe indicates."

 

Source: "Complete Guide to Home Canning," Agriculture Information Bulletin No. 539, USDA (Revised 2009).

 

30 minutes of 180º to 185º F processing time vs, the shorter processing times in a boiling-water canner as in the following recipe.....

 

http://nchfp.uga.edu/how/can_06/quick_dill_pickles.html

Edited by DiggingDogFarm (log)

~Martin :)

I just don't want to look back and think "I could have eaten that."

Unsupervised, rebellious, radical agrarian experimenter, minimalist penny-pincher, and adventurous cook. Crotchety, cantankerous, terse curmudgeon, non-conformist, and contrarian who questions everything!

The best thing about a vegetable garden is all the meat you can hunt and trap out of it!

 

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Right, right, right. I got 'ya. (Sometimes it takes a hammer, I swear!)  Thanks for the add'l post!

 

As I said above, the processing time has already been necessarily increased in safe 180º to 185º F recipes to compensate for the lower temperature so there's no need for further adjustments.

 

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I realized the genesis of my confusion today, while canning apricots. I'll add the info here, for completeness of the thread.

 

In "Blue Ribbon Preserves," by Linda J. Amendt, on p 35, there is a chart of processing temps for various foods. Example: "Fruit (whole or pieces) 190F- to 200F.  Times vary depending on the type of fruit, size of pieces and method of preparation. (See recipe for exact time.)"

Below this chart she writes, "If you live at an altitude above 1,000 feet, you will need to make some adjustments for the altitude by adding additional time to the standard water bath processing times given above."  Another chart follows, giving the increases of processing times for altitude.  Next to this comment, I had penciled in, "Why needed if proper temp (ie 290) can be achieved???)

 

It seems to me, something is not quite right with her instructions.  Or I am mis-understanding them.

 

Example:

Following "Blue Ribbon Preserves" instructions I would process quart jars of hot pack apricots at 190-200F for 30 min plus 10 more minutes for my elevation, for a total of 40 min.

Following Natinal Center for Home Food Preservation Guidelines, I would process the same at boiling for 25 minutes plus 10 min more for my elevation, for a total of 35 minutes.

 

FWIW, water boils at about 203F at my current elevation.

 

For now, I use the NCHFP Guidelines, although I am curious if there is an "approved" way to process FRUIT at 190, to see if the quality of the product improves.  (I realize there is an NCHFP approved method for low-temp processing for PICKLES.)

Edited by operaflute (log)
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