Preserving Floyd: Home Canning Essentials

Home processing of food sealed in jars to be shelf-stable and stored at room temperature is a simple and safe method of preservation as long as a few simple rules are adhered to.  The busiest months of the canning year are about to begin and it's good to start off with some basics for the novices out there embarking on their first canning adventures.

#1 Most Important Rule - All safe canning (both water bath and pressure canning) comes down to two facts: Acidity and Temperature.
Most fruits are considered high acid (except for tomatoes which are on the acidity cusp) and can be processed in a boiling water bath which will bring the internal temperature of the jars to 212F (the temperature of boiling water).  No matter how long you leave a jar in a boiling water bath the internal temp will never rise above 212F.  The length of time in the bath specified in a recipe is how long it takes for the heat to penetrate the density of the canned product and raise it to 212F.

Most vegetables (and meats) are low acid and must be processed in a pressure canner where temperatures above 212F can be achieved.  Steam under pressure becomes hotter than plain boiling water.  For example, water boiling under 10 pounds of pressure (a typical poundage for many pressure canned foods) reaches a temperature of 240F.  Again, the time specified in the recipe is how long it takes to raise the heat in the center of the jar to the desired temperature.  In recipes for pressure canned food you will find both the pounds pressure and the length of time to be held at that pressure specified. Below is a chart showing the acidity of some foods.

High Acidity Foods Using Boiling-Water Bath or Pressure Canning (for less processing)		Low Acidity Foods Using Pressure Canning Only
Apples	Plums	Artichokes (Jerusalem)	Mushrooms
Apricots	Raspberries	Asparagus	Okra
Blackberries	Rhubarb	Beans (green or yellow)	Parsnips
Blueberries	Strawberries	Beets	Peas
Cranberries	Pineapple	Broccoli	Peas (snap)
Cherries	Tomatoes (with acid added)	Brussels Sprouts	Peppers
Cucumbers (pickled)		Cabbage	Potatoes
Grapefruit		Carrots	Pumpkin
Grapes		Cauliflower	Spinach
Nectarines		Corn	Squash (summer)
Oranges		Eggplant	Squash (winter)
Peaches		Figs	Sweet Potatoes
Pears		Lima Beans

Chart courtesy of http://www.recipetips.com/kitchen-tips/t--1396/canning-temperatures-and-processing-times.asp