A food or food mixture that contains sufficient acid naturally or added as an ingredient to provide a pH value of 4.6 or lower. Fruits, fruit juices, tomatoes, jams, jellies and most soft spreads are naturally high-acid foods. Food mixtures such as pickles, relishes, salsas and chutneys contain added vinegar or citric acid, which lowers their pH, making them high-acid foods. High-acid foods can be safely processed in a boiling water canner.

A type of pectin that requires a high sugar content and the presence of acid to produce a gel when making jams and jellies. Powdered and liquid commercial pectin products are usually high-methoxyl.

The process of preserving fresh or prepared foods in glass jars with two-piece closures, using heat processing to destroy microorganisms that cause spoilage. See also fresh preserving.

Filling jars with preheated, hot food prior to heat processing. Preheating food expels excess air, permits a tighter pack in the jar and reduces floating. This method is preferred over the raw-pack method, especially for firm foods.

A fresh preserving method in which hot foods are ladled into jars, two-piece closures are applied and the jars are turned upside down (inverted) for a period of time. Since no heat processing takes place, this method is not recommended.

A soft spread made by combining crushed or chopped fruits with sugar and cooking to form a gel. Commercial pectin may or may not be added. Jams can be made with a single fruit or with a combination of fruits. They should be firm but spreadable. Jams do not hold the shape of the jar.

A glass container used in fresh preserving to preserve food and/or liquids. For safe fresh preserving, jars must be designed to seal with two-piece metal closures and to withstand the temperatures and reuse associated with fresh preserving. See also mason jar.

A soft spread made by combining fruit juice or acidified vegetable juice with sugar and cooking to form a gel. Commercial pectin may or may not be added.

A mesh cloth bag used to strain juice from fruit pulp when making jellies. A strainer lined with many layers of cheesecloth may be substituted. Both the jelly bag and cheesecloth need to be dampened before use.

A stainless steel tripod stand fitted with a large ring. A jelly bag is placed over the ring. The stand has feet that hold it onto a bowl to allow juice to strain from the bag into the bowl.

See salt, kosher.

A metric unit of atmospheric pressure (force).

A metric unit of volume. One liter is similar in volume to 1 U.S. quart.

The acid produced during fermentation. The fermentation process converts the natural sugars in food to lactic acid, which, in turn, controls the growth of undesirable microorganisms by lowering the pH (increasing the acidity) of the food product and its environment. Lactic acid also adds a distinctive tart flavor and transforms low-acid foods into high-acid foods that can be safely processed in a boiling water canner.

Juice extracted from lemons that is added to food products to increase the acidity. Lemon juice can also be purchased commercially. In fresh preserving, lemon juice is added to certain foods to increase acidity and ensure proper processing. In some soft spread recipes, especially those prepared with added pectin, the acid in the lemon juice also aids with gelling. The acidity of freshly squeezed lemon juice is variable, depending on the lemon variety and harvest conditions, whereas bottled lemon juice is produced to consistent acidity standards. In recipes that specify bottled lemon juice, it is crucial for the success of the final product not to use freshly squeezed lemon juice. Where bottled is not specified, either freshly squeezed or bottled lemon juice may be used.