Woman's Institute Library of Cookery. Volume 5: Fruit and Fruit Desserts; Canning and Drying; Jelly Making, Preserving and Pickling; Confections; Beverages; the Planning of Meals

by Woman's Institute of Domestic Arts and Sciences

STEAM-PRESSURE METHODS

43. For canning foods by steam pressure, special equipment is necessary. In one of the steam-pressure methods, what is known as a water-seal outfit is required, and in the other a device called a pressure cooker is employed. The work of getting the containers ready, preparing the food for canning, packing it into the jars, and sealing and testing the jars is practically the same in the steam pressure methods as in the cold-pack methods. The difference lies in the cooking and sterilization of the foods after they are in the jars and partly sealed and in the rapidity with which it may be done.

44. CANNING WITH A WATER-SEAL OUTFIT.--A water-seal outfit, which may be purchased in stores that sell canning supplies, consists of a large metal vessel into which fits a perforated metal basket designed to hold jars of food. This vessel is also provided with a tight-fitting cover having an edge that passes down through the water, which is placed in the bottom of the vessel. When heat is applied to the bottom of the vessel, the water inside of it is changed into steam. The cover prevents the steam from passing out, and it collects in and around the metal basket supporting the jars of food. Enough steam is generated in this outfit to raise the temperature about 4 to 6 degrees above the boiling point. Thus, the water-seal outfit will cook the food in the cans in about one-fourth less time than will the water bath of the one-period cold-pack canning method.

45. CANNING WITH A PRESSURE COOKER.--For canning by steam pressure, a number of different kinds of pressure cookers are to be had, but in principle they are all alike and they are always made of heavy material, so as to withstand the severe steam pressure generated in them. In Fig. 20 is shown one type of pressure cooker. It is provided with a bail, or handle, for carrying it and with clamps that hold the cover firmly in place. Attached to the cover is a steam gauge, which indicates the steam pressure inside the cooker, and a pet-cock, which is used to regulate the pressure. On some cookers, a thermometer is also attached to the cover. Also, inside of some, resting on the bottom, is an elevated rack for supporting the jars of food that are to be sterilized and cooked. In operating a pressure cooker, water for generating steam is poured in until it reaches the top of this rack, but it should not be allowed to cover any part of the jars of food. Steam is generated by applying heat to the bottom of the cooker, and the longer the heat is applied the higher the steam pressure will go.

It is possible to secure a steam pressure of 5 to 25 pounds per square inch in a cooker of this kind. This means that the temperature reached will vary from a few degrees above boiling to about 275 degrees Fahrenheit. At a pressure of 20 pounds, the temperature will be about 260 degrees. The heavier the material used for a cooker and the more solid the construction, the higher may go the steam pressure, and, of course, the temperature. Some cookers of light construction will not permit of a pressure greater than 5 pounds, but even such cookers are very satisfactory. It is the high temperature that may be developed in a pressure cooker that greatly shortens the time required for cooking jars of food and making them sterile.