Putting Food By - Janet Greene [6]
We mention this now because we use a Hot–Water Bath in processing a number of canned fruit juices. The individual instructions specify the simmer temperature needed—180 F/82 C to 190 F/88 C—but again this is at sea level, so at higher altitudes increase Hot–Water Bath processing time for such foods.
Pasteurization is the partial sterilization of food, and it was devised in the nineteenth century by Louis Pasteur as a means of controlling the fermentation of wine. As applied to milk, one method raises the temperature to 142–145 F/61–63 C, holds it there for 30 minutes, then quickly reduces the temperature to well below 50 F/10 C, where is is held for storage. The other way—called the “flash” method and used commercially by dairies—raises the temperature to 160–165 F/71–74 C for a mere 15 seconds, followed by rapid cooling to well below 50 F/10 C.
In addition we use the term pasteurizing in connection with the Hot–Water Bath for processing canned fruit juices (Chapter 7) and to ensure a safe seal for pickles, etc., in Chapter 19. Note that PFB recommends a “finishing” treatment by dry heat at 175 F/80 C for foods dried in open-air/ sun.
Canning at High Altitude
The thumbnail tables on page 14 were given to PFB by Dr. Gerald Kuhn of Pennsylvania State University, who organized, at the Center for Excellence, research for and publication of The Complete Guide to Home Canning (1988/89). They are generally in accordance with current USDA recommendations, although USDA Complete Guide to Home Canning (2006) recommends slightly longer processing times for some fruits when canning in a Boiling–Water Bath at altitudes above 6000 feet. It is these tables that householders are referred to when advised to insert their own altitude adjustments in the instructions for specific foods in Chapters 7 through 12.
These tables provide simple rules for using both dial-gauge Pressure Canners and deadweight-gauge (or weighted-gauge) Pressure Canners at high altitudes. To summarize, if using a dial-gauge Pressure Canner, the pressure in the canner must be increased by 1 pound of pressure for each 2000 feet above sea level in order to reach the required temperature of 240 F/116 C. If using a weighted-gauge canner, the 15-pound weight must be used at all altitudes above 1000 feet in order to reach the required temperature. Although it has been accepted wisdom in the Canadian and American Rockies to add processing time to 15-psig instructions, additional time is not necessary if the pressure of the canner is adequately adjusted.
DR. KUHN’S RULES OF THUMB FOR CANNING AT ALTITUDE
(If your county’s Cooperative Extension Service has no recommendations for your particular area, ask your State University CES for help.)
If the base Boiling–Water Bath time, always given as for the sea-level zone, is 20 minutes or less, increase the time by increments of 5, thus (using Hot-packed pints of stewed rhubarb as our example):
0–1000 ft/0–305 m = 10 minutes
1001–6000 ft/305–1829 m = 15 minutes
6001–9000 ft/1829–2743 m = 20 minutes
If the base Boiling–Water Bath time is more than 20 minutes (as, say, for a pint of Hot-packed quartered tomatoes with an added 1 tablespoon of bottled lemon juice):
0–1000 ft/0–305 m = 35 minutes
1001–3000 ft/305–914 m = 40 minutes
3001–6000 ft/914–1829 m = 45 minutes
6001–(9000) ft/1829–(2743) m = 50 minutes
For Pressure-processing low-acid foods in a Dial-Gauge Pressure Canner (“psig” = pounds per square inch by gauge)—using as our example the ever-present green/snap/wax bean, Hot-packed in pints and processed for 20 minutes:
0–1000 ft/0–305 m = 11 psig for 20 minutes
1001–3000 ft/305–914 m = 12 psig for 20 minutes
3001–5000 ft/914–1524 m = 13 psig for 20 minutes
5001–7000 ft/1524–2134 m = 14 psig for 20 minutes
7001 + ft/2134 + m = 15 psig for 20 minutes
For Pressure-processing low-acid food in a