Reference > Cooking Methods & Techniques > Canning > Cold-Pack Method

Cold-Pack Method

The cold-pack method of canning differs from the open-kettle method in that the food to be canned is not cooked in a kettle before placing it in the jars and sealing them. In this method, the food to be canned is prepared by washing, peeling, scraping, hulling, stemming, seeding, or cutting, depending on the kind. Then it is scalded or blanched and plunged into cold water quickly and taken out immediately, the latter operation being called cold-dipping. After this it is placed into hot jars, covered with boiling liquid--boiling water and salt for vegetables, meats, fish, or soups, and boiling sirup for fruits. Then the filled jars are covered loosely and placed in a water bath and processed; that is, cooked and sterilized. When food that is being canned is subjected to processing only once, the method is referred to as the one-period cold-pack method; but when the food in the jars has not been blanched and cold-dipped and is processed, allowed to stand 24 hours and then processed again, and this operation repeated, it is called the fractional-sterilization method. The equipment required for the cold-pack canning method and the procedure in performing the work are taken up in detail, so that every point concerning the work may be thoroughly understood.

Utensils Required

The utensils required for canning by the cold-pack method are shown assembled.

Utensils for cold-pack method

Chief among them is a sterilizer, or boiler, which consists of a large fiat-bottomed vessel fitted with a rack and a tight-fitting cover. A number of such devices are manufactured for canning by the cold-pack method, but it is possible to improvise one in the home. A wash boiler, a large pail, a large lard can, or, in fact, any large vessel with a flat bottom into which is fitted a rack of some kind to keep the jars 3/4 inch above the bottom can be used. Several layers of wire netting cut to correct size and fastened at each end to a 3/4-inch strip of wood will do very well for a rack. In any event, the vessel must be deep enough to allow the water to cover the jars completely and must have a tight-fitting cover. Besides a sterilizer, there are needed three large vessels, one for scalding the food that is to be canned, one for cold-dipping, and one for keeping the jars hot. To hold the food that is to be dipped, a sieve, a wire basket, or a large square of cheesecloth must also be provided, and for placing jars in the water bath, a can lifter may be needed. The remainder of the equipment is practically the same as that described under the heading General Equipment for Canning.

Procedure in the One-Period Cold-Pack Method

Preparing the Containers

The first step in the cold-pack method consists in preparing the containers for the food. The jars, rubbers, and covers, however, do not have to be sterilized as in the open-kettle method. But it is necessary first to test and cleanse the jars and then to keep them hot, so that later, when they are filled and ready to be placed in the water bath, they will not crack by coming in contact with boiling water. The best way in which to keep the jars hot is to let them stand in hot water.

Preparation of the Food

Attention should next be directed to the preparation of the food to be canned; that is, clean it and have it ready for the processes that follow. The fruits or vegetables may be canned whole or in pieces of any desirable size. What to do with them is explained later, when the directions for canning the different kinds are discussed. While the food is undergoing preparation, fill the sterilizer with hot water and allow it to come to the boiling point.

Scalding and Blanching

When the food is made ready, the next step is to scald or blanch it. Scalding is done to loosen the skin of such food as peaches, plums, and tomatoes, so that they may be peeled easily. To scald such fruits or vegetables, dip them quickly into boiling water and allow them to remain there just long enough to loosen the skin. If they are ripe, the scalding must be done quickly; otherwise they will become soft. They should never be allowed to remain in the water after the skin begins to loosen. For scalding fruits and vegetables a wire basket or a square of cheesecloth may be used.

Wire basket
Cheesecloth

Blanching is done to reduce the bulk of such foods as spinach and other greens, to render them partly sterilized, and to improve their flavor. It consists in dipping the food into boiling water or suspending it over live steam and allowing it to remain there for a longer period of time than is necessary for scalding. To blanch food, place it in a wire basket, a sieve, or a piece of clean cheesecloth and lower it into boiling water or suspend it above the water in a closely covered vessel. Allow it to remain there long enough to accomplish the purpose intended.

Cold Dipping

After the food to be canned is scalded or blanched, it is ready for cold-dipping. Cold-dipping is done partly to improve the color of the food. It stops the softening process at once, makes the food more firm and thus easier to handle, and helps to loosen the skin of foods that have been scalded. It also assists in destroying bacteria by suddenly shocking the spores after the application of heat. Cold-dipping, in conjunction with blanching or scalding, replaces the long process of fractional sterilization, and is what makes the one-period cold-pack method superior to this other process. To cold-dip food, simply plunge that which has just been scalded or blanched into cold water, and then take it out at once.

Cold dipping

Packing the Jars

Packing the jars immediately follows cold-dipping, and it is work that should be done as rapidly as possible. Remove the jars from the hot water as they are needed and fill each with the cold-dipped fruit or vegetable. Pack the jars in an orderly manner and as solidly as possible with the aid of a spoon.

Packing the jars

Just this little attention to detail not only will help to improve the appearance of the canned fruit, but will make it possible to put more food in the jars.

When a jar is filled, pour into it whatever liquid is to be used.

Pouring liquid in jar

As has been stated, hot sirup is added for fruits and boiling water and salt for vegetables. However, when fruit is to be canned without sugar, only water is added. With tomatoes and some greens, no liquid need be used, because they contain a sufficient amount in themselves.

Preparation for the Water Bath

As the jars are filled, they must be prepared for the water bath. Therefore, proceed to place the rubber and cover on the jar. Adjust the rubber so that it will be flat in place.

Adjust the rubber

Then put the cover, or lid, on but do not tighten it.

Putting the cover on

The cover must be loose enough to allow steam to escape during the boiling in the water bath and thus prevent the jar from bursting. If the cover screws on, as in the jar at the left, do not screw it down tight; merely turn it lightly until it stops without pressure being put upon it. If glass covers that fasten in place with the aid of a clamp are to be used, as in the jar at the right, simply push the wire over the cover and allow the clamp at the side to remain up. Jars of food so prepared are ready for processing.

Processing

The purpose of the water bath is to process the food contained in the jars before they are thoroughly sealed. Therefore, when the jars are filled, proceed to place them in the water bath. The water, which was placed in the sterilizer during the preparation of the food, should be boiling, and there should be enough to come 2 inches over the tops of the jars when they are placed in this large vessel. In putting the jars of food into the sterilizer, place them upright and allow them to rest on the rack in the bottom. If the filled jars have cooled, they should be warmed before placing them in the sterilizer by putting them in hot water. On account of the boiling water, the jars should be handled with a jar lifter.

Jar lifter

However, if the sterilizer is provided with a perforated part, all the jars may be placed in it and then lowered in place.

Lowering the jars

When the jars are in place, put the tight-fitting cover on the sterilizer and allow the water to boil and thus cook and sterilize the food in the jars. The length of time for boiling varies with the kind of food and is given later with the directions for canning different foods. The boiling time should be counted from the instant the water in the sterilizer begins to bubble violently. A good plan to follow, provided an alarm clock is at hand, it to set it at this time, so that it will go off when the jars are to be removed from the sterilizer.

Sealing the Jars

After processing the food in this manner, the jars must be completely sealed. Therefore, after the boiling has continued for the required length of time, remove the jars from the water with the aid of the jar lifter or the tray and seal them at once by clamping or screwing the covers, or lids, in place.

Clamping the covers

Sometimes, the food inside the jars shrinks so much in this process that the jars are not full when they are ready to be sealed.

Shrinkage

Such shrinkage is usually the result of insufficient blanching, or poor packing or both. However, it will not prevent the food from keeping perfectly. Therefore, the covers of such jars of food must not be removed and the jars refilled; rather, seal the jars tight immediately, just as if the food entirely filled them. If, in sealing jars removed from the water bath, it is found that a rubber has worked loose, shove it back carefully with the point of a clean knife, but do not remove the cover.

As the jars are sealed, place them on their sides or stand them upside down, to test for leaks, in a place where a draft will not strike them and cause them to break.

Testing for leaks

If a leak is found in any jar, a new rubber and cover must be provided and the food then reprocessed for a few minutes. This may seem to be a great inconvenience, but it is the only way in which to be certain that the food will not be wasted by spoiling.

Wrapping and Labeling

When the jars of food have stood long enough to cool, usually overnight, they are ready for wrapping and labeling. Wrapping is advisable for practically all foods that are canned, so as to prevent bleaching, and, of course, labeling is necessary when canned food is wrapped, so as to enable it to be distinguished readily when it is in storage. To wrap canned foods, proceed as in the illustration.

Wrapping canned foods

Use ordinary wrapping paper cut to a size that will be suitable for the jar, and secure it in place with a rubber band, as shown, or by pasting the label over the free edge.

Procedure in the Fractional-Sterilization Method

In canning food by the fractional-sterilization canning method, the procedure is much the same as in the one-period cold-pack method. In fact, the only difference between the two is that blanching and cold-dipping are omitted, and in their stead the food in the jars is subjected to three periods of cooking. When the jars of food are made ready for processing in the sterilizer, they are put in the water bath, boiled for a short time, and then allowed to cool. After 24 hours, they are again boiled for the same length of time and allowed to cool. After another 24 hours, they are subjected to boiling for a third time. Then the jars of food are removed and sealed as in the one-period cold-pack method. By the fractional-sterilization method, the spores of bacteria contained in the food packed in the jars are given a chance to develop during the 24-hour periods after the first and second cookings, those which become active being destroyed by cooking the second and third times. Although some canners prefer this method to those already mentioned, the majority look on it with disfavor, owing to the length of time it requires.

Source

Woman's Institute Library of Cookery, Volume 5.

Print

Print recipe/article only


comments powered by Disqus