Canning High Acid Foods
by: Val Hillers, Ph.D. , Extension Food Specialist
Acid foods are foods that contain enough acid to have a pH of 4.6 or lower. Acid foods can be processed safely in a boiling water canner.
"Acid" foods can be:
- naturally acid foods
- foods that have acid, such as vinegar or lemon juice, added
- fermented foods, such as sauerkraut. During the fermentation process bacteria produce an acid.
Naturally acid foods include:
- most fruits (except figs, Asian pears, melons, bananas, dates, papaya, ripe pineapple, persimmons)
- most tomatoes
Processing In A Boiling Water Canner
Boiling water canning is recommended as a safe method for processing acid foods. Not all bacteria in these canned foods are killed. However, surviving bacteria can't grow in foods with pH values of 4.6 or lower. If, the pH of canned foods is above 4.6, surviving bacteria, includingClostridium botulinum, will grow in the food.
An increase in pH ofacid foods may be caused by growth of several bacteria and mold species when these foods are underprocessed. It's imperative, then, that acid foods be processed in boiling water for sufficient time to kill all organisms capable of growing at or below a pH of 4.6.
Water boils at a lower temperature at high altitudes, e.g., 203°F at 5,000 feet. Because of this, the processing time must be lengthened. Use the canning guides or instructions in the recipe, if they are given for high altitudes. If no such instructions are given, follow the guidelines below.
- If processing time given in the directions is 20 minutes or less, add one extra minute per 1,000 feet above sea level.
- If the processing time given in the recipe is more than 20 minutes, add two extra minutes per 1,000 feet above sea level.
When canning in boiling water, a longer processing time is needed for most raw-packed foods than is needed for hot-packed foods. Quart jars are processed longer than pint jars. Processing times for half-pint and pint jars are the same. Processing times for 1 1/2 pint and quart jars are the same.
Follow these steps for successful boiling water canning:
- Fill the canner halfway with water
- Preheat water to about 140°F for raw-packed foods or to 180°F for hot-packed foods.
- Fill jars, put on properly fitting lids, load into the canner rack and use the handles to lower the rack into the water; or, fill the canner, a jar at a time, with a jar lifter.
- Add more boiling water, if needed, so the water level is at least one inch above jar tops. Cover with the canner lid.
- Turn heat to its highest position until water boils vigorously.
- Set a timer for the minutes required for processing the food.
- Lower the heat setting to maintain a gentle boil throughout the processing schedule.
- When jars have boiled for the recommended time, turn off the heat, and remove the canner lid.
- Using a jar lifter, remove the jars immediately and place them on a towel, leaving at least one inch of space between the cooling jars.
Select only disease-free, preferably vine-ripened, firm fruit for canning. Do not can tomatoes from dead or frost-killed vines. Green tomatoes are more acidic than ripened fruit and can be substituted for ripe tomatoes in any canning recipe.
Some tomatoes are low in acid. To ensure safe acidity in whole, crushed, or juiced tomatoes, add two tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, use one tablespoon bottled lemon juice or 1/4 teaspoon citric acid. Sugar to taste may be added to offset the acid taste.
NOTE: The addition of acids will not increase the acidity of overripe tomatoes enough to make them safe for home canning.
Fruits with a desirable color, a pronounced flavor, and evenly ripened and uniform in size and shape will yield the most attractive product when canned. Expect many variety and seasonal differences in quality. Sort and discard small diseased fruits. Trim out minor diseased spots on large fruits. Wash fruit carefully, but avoid soaking. Peel apples that have fallen from trees.
Canning fruits with and without sugar
Sugar helps canned fruits hold their shape, color, and flavor. The sugar moves into the fruit tissue and keeps it firmer. Sugar is usually added as a syrup. Extra-thin or thin syrup adds fewer calories than heavier syrups, costs less and results in less floating of fruits. It is safe to can fruits without sugar using the same processing time you would use with sugar. Either water or fruit juice may be used for the liquid. Canning with artificial sweeteners is not advised. They lose some sweetening power when heated and may become bitter. Add sugar substitutes when fruit is served.
Preventing darkening in canned fruit. Light colored fruits, such as apples, apricots, peaches, and pears tend to darken when canned. To prevent this, hold peeled or pitted fruit in water containing ascorbic acid (vitamin C). To make an ascorbic acid solution, crush and dissolve six 500 mg. vitamin C tablets in a gallon of water.
Additional steps which help prevent darkening:
- cover fruit completely with hot liquid before closing jar
- remove air bubbles
- use recommended headspace
- tighten lids properly
- process foods for the recommended times