Identifying Acidity Levels in Food to
Determine Canning Method
It is important to identify the acidity level (pH) of the food you plan to process to determine the type of canning method that is required to process (heat) the food for safe consumption: water bath (boiling water canner) or pressure canning (steam pressure canner).
For the purpose of canning, all foods are divided into two classifications determined by the amount of natural acid present in the food or the acidification of the food to a specific pH level. The two classifications are:
High Acid Foods and Acidified Foods
These foods have naturally high levels of acid or have a sufficient amount of acid added to them. Bottled lemon juice, citric acid or vinegar labeled 5 percent acidity are sometimes added to canning recipes to increase acidity. Foods in this category must have a pH of 4.6 or less. The boiling water method of process is adequate for high acid foods.
Generally all fruits and soft spreads are classified as high acid foods. Figs and tomatoes require the addition of an acid so they may be safely canned using the boiling water method. Fermented foods, such as sauerkraut and brined pickles, and foods to which a sufficient amount of vinegar is added are also treated as high acid foods.
Low Acid Foods
These foods have very little natural acid. Vegetables, meats, poultry and seafoods are in the low-acid group. Soups, stews, meat sauces and other recipes which contain a combination of high acid and low acid ingredient yet remain with a pH level greater than 4.6, must be process as a low acid product. The pressure canning method (higher heat) is adequate for low acid foods.
If you are unsure of the acidity level and want to test it yourself, purchase litmus paper at a teacher or scientific supply store then test the acidity level of the food you want to can. Litmus paper is an acid-sensitive paper that measures the acid in food. The paper changes color when inserted in food. Then you compare the color with the pH chart of colors that accompanies the litmus paper.
The pH (potential of hydrogen) is the measure of acidity or alkalinity in food. The values range from 1 to 14. Neutral is 7. Lower values are more acidic, while higher values are more alkaline. The lower the pH value in your food, the more acidic it is.