UNIVERSITY OF CALIFORNIA

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Date: April 30, 1974 To: Home Advisors and Dairy Farm Advisors DAVis, CALIFORNIA Cooperative Extension

From: John C. Bruhn Title: Extension Food Technologist Address: 235 Cruess Hall~UCD Re: "How to Make "

I was asked by a group of students on campus to prepare a brief handout on the home manufacture of yogurt. The enclosed publication represents this effort. You will note that five recipies are given for the home manufacture. These recipies have been tested and do provide a satisfactory product provided an active yogurt starter is used. You might note that recipe B indicates an incubation temperature of 43®C. You might want to change that to 110°F in copies distributed to the public.

Please feel free to use any part or all of this publication as it may suit your individual needs.

Your comments would be welcomed.

JCB /sr Enclosure cc:Gertie Thomas Kastanis Public Service, Mrak Hall

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CO-OPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS, U. S. Department of Agriculture and University of California co-operating For Interdeiiiirtinentiil Use Oiilv HOMEMADE CULTURED PRODUCTS

by

J. C. Bruhn Extension Food Technologist Dept. of Food Science & Technology University of California Davis, CA 95616

YOGURT RECIPIES — Introduction

There is little doubt that fermented have been consumed since man first milked cows. Prior to modern times there were no means nor knowledge of, the necessity for proper sanitation, adequate refrigeration , or heat treatment of milk to prevent spoilage. Milk left unconsumed would naturally ferment, and the characteristics of the resulting product were dependent upon the microorganisms present in the original milk.

It wasn't until about 100 years ago that man first discovered these microscopic organisms, and learned they were responsible for the many favorable and unfavorable changes that occur in raw milk and other foods. Since that time, man has learned how to best control fermentations and to produce uniform, high-quality products.

Modern methods for making in dairy processing plants are highly technical. They involve extreme precautions to protect all ingredients from contamination with microorganisms which may cause difficulties during manufacturing or defects in the finished product.

The simple procedures described in this publication for making cultured butter¬ milk, and yogurt in the home take advantage of knowledge employed by the highly-trained dairy plant processor. This is accomplished by recommending the homemaker buy some of the freshly-made products by the plant. These products can be used as bacterial starters to ferment like products in the home.

The Nature of Fermentations

The term "cultured" as it applies to dairy products, means controlled fermentation (by known types of harmless, active bacteria) to produce products having de¬ sirable flavor and body characteristics.

Anyone acquainted with the production and care of milk knows that if it is not handled under strict sanitary conditions, and if it has not been refrigerated properly, it will quickly spoil. The type of fermentation which takes place under such conditions, however, may differ widely from one experience to the next. The nature of natural fermentation is related to the microorganisms present. The fermentations are desirable in most cultured dairy products:

1. Lactic Acid Fermentation — Some microorganisms break down lactose (milk sugar) to produce lactic acid, which is a sour compound. When enough acid has been developed, it will coagulate (clabber) the protein of the milk.

2. Citric Acid Fermentation — Other microorganisms produce certain aroma and flavor compounds from citric acid which are pleasing to the consumer. Thus, a good type of fermentation would involve some of these types of microorganisms as well as lactic acid-producing microorganisms. Page 2

Controlled Fermentation is Necessary

Pure cultures of bacteria are necessary to develop the desired flavor and aroma in dairy products. Dairy plant laboratories obtain these pure cultures from specialized laboratories and grow them under strict sanitary conditions, using utmost pre¬ cautions to prevent contamination with other microorganisms. These cultures are used as "starters" to fermend commercially processed cultured , sour cream, yogurt, cottage cheese, and other cheeses.

Before such products are cultured with a starter, the raw milk or cream must be heat- treated to destroy microorganisms which may be present. The elimination of un¬ desirable microorganisms prevents their interfering with proper fermentation and the development of desirable flavor and aroma. Milk and cream used for homemade cultured products should also be heat-treated to destroy troublesome microorganisms and to make good-flavored, wholesome products. Products made by dairy plants, since they contain pure cultures of the right kinds of bacteria, are ideal for use as starters for homemade products. Purchase the freshest products to be used as starters, since bacteria become less active with age.

Yogurt

Yogurt is a coagulated, sour made from fresh, whole milk with added solids, either from nonfat dry milk or evaporated milk. It is a popular dairy food in southeast Europe, southern Asia, and northern Africa. The bacterial culture used in making yogurt differs from those used in making most other cultured dairy products. These bacteria grow best between 105° to 110°F., a temperature at which the growth of most other bacterial is retarted. Yogurt may be eaten "as is"; as a custard with berries, peaches, or apple pie; seasoned with salt and chives or chopped green onions; as a topping for fruit; or served with sweets such as honey, maple syrup, jelly, or molasses. Anyone who like buttermilk should like yogurt.

Yogurt may be made in the home by one of the following procedures.

A. 1. Add one ounce of nonfat dry milk or one 13 oz. can of evaporated milk to 3/4 qt. of clean, fresh milk in the top part of a double boiler.

2. Heat the fortified milk to 190° to 205°F. and hold it at that termperature for one hour. Keep the cover on the double boiler during .

3. Cool the milk to 120°F. and pour it into a clean quart jar or other suitable container that has been sterilized in boiling water or by steaming. Cool to 110°F.

4. Add 3 tbsp. of yogurt milk obtained from the local grocery. Mix it thoroughtly with the milk. Cover.

5. Place the jar in a pan of water which is maintained at 108°F. Allow the milk to ripen at that temperature until it is thick and has developed a tart, acid flavor. The ripening period required 3-1/2 to 5 hours.

6. Remove the ripened yogurt from the water bath and place it in the refrigerator to chill and store until used. • ^ *■ Page 3

B. To make about 2 quarts of high protein yogurt:

1. Mix 1-1/2 cups of powdered skim milk, 3 tbsps. of commercial plain yogurt, and a large can (13 oz.) evaporated milk into 1-1/2 quarts of lukewarm water.

2. Incubate at about 110°F for 3 to A hours, or until thick; longer time gives a tangier product.

C. Ingredients: 1 quart milk, 2 tbsps. "starter" (commercial yogurt). Utensils: Saucepan, crockery bowl and cover, dish towel, two heavy towels.

1. Bring milk to a boil, slowly, over low fire. It must not boil over. The instant it boils, pour into crockery (not metal) bowl. Cool until a little warmer than lukewarm (105°F).

2. Pour 1/2 cup of milk into a bowl and blend into it wo heaping tbsps. of commercial yogurt. Stir well, and then blend this mixture into remaining warm milk.

3. Cover crockery bowl with dry dish towel; then put on crockery bowl cover; and finally completely wrap bowl in two heavy turkish towels. Store in warm place for at least 7 hours (or overnight).

4. Remove towels and cover. Blot up any liquid that has formed on top of yogurt. Spoon out three heaping tablespoons and place in glass (not metal) jar, storing in refrigerator until needed as starter for the next batch. Add salt to the remaining yogurt and store in glass jar in refrigerator.

If you prefer a sharper tang, the leavening time should be lengthened.

D. Same as C except under ingredients, add 1 package unflavored gelatin.

1. Add package gelatin to cold milk.

2. Continue on as for recipe C.

E. 1. Use whole milk of the highest quality and add 5% dry skim milk (by weight) or equal quantities of evaporated milk to the whole milk.

2. Heat the concentrated whole milk to boiling (212''F) and cool at once to 115°F. Heating to 180° for 30 minutes will suffice. Cool to 115°

3. Add 2% of plain commercial yogurt starter (2 tbsps. to each pint of milk) to the milk at 115°F., and mix thoroughly.

4. Put the inoculated milk in 1/4-pint bottles and cover with loose fitting caps, or use any other type of small container with suitable cover. Custard cups or jelly glasses are satisfactory for home use since the yogurt can be eaten directly from the container in which it is made.

5. Incubate the containers of inoculated milk at 112° to 115°F., in water or in an incubator for 3 hours or until coagulation is complete.

6. Place the containers of coagulated milk in a refrigerator to cool. The yogurt may be eaten as soon as it is cool enough. Yogurt will keep for a week or longer if it is held at 50°F., or lower.