Yesterday, my girlfriend wanted to make jam from strawberries we purchased at the Farmers’ Market (which are in season!). After purchasing the strawberries she posed a question I had not been asked nor had ever given much thought, “How much longer do I need to boil the jarred jam to make sure it is safe since we are not at sea level?” Boiling water!
We live at roughly 2,400 ft above sea level, close to the Appalachian Mountain Range, and water boils at 208°F instead of the normal 212°F. Many people only think of Colorado as having to worry about altering cooking (processing) procedures for living elevation, but anyone living over 1,000 feet above sea level will most likely have to alter their recipes to ensure safe food.
So why does water boiling at a temperature of 4°F lower than usual affect the processing time? The answer to this question is bacteria. As with any heat processing step, the objective is to kill bacteria and the spores they produce. All bacteria have a “D-value,” the duration for which foods must be cooked at a specific temperature to ensure that the harmful bacteria are either killed or their toxins or spores are inactivated. For example, a D-value may be heating a food at 212°F for 10 minutes; however, if you are living at altitude and water is only boiling at 208°F, then the water bath is not hot enough to kill all of those bacteria, spores, or toxins. Since there is nothing you can do about how hot the water will become, the duration of the heat step must be elongated.
In my case, an extra 5 minutes was added to the original processing time of 10 minutes to ensure that we will not become ill when we enjoy the fruits of our labor later.
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- Home Canning (Jamming) at Altitude - June 7, 2013