This is Frontier's nitrogen-flushed double-wall silverfoil pack. Some Frontier packs are double-walled wax-lined paper.

Yogurt is cultured milk made with Lactobacillus acidophilus, L. thermophilus, L. bulgaricus, or other other beneficial lactic-acid bacteria.

Lactobacillus acidophilus is a 'friendly' bacterium (called a probiotic) that inhabits the intestines. It helps prevent bacterial disease, partly through the production of lactic acid.

This makes it, and foods containing it, medically useful in maintaining normal intestinal flora, preventing and treating diarrhea and vaginal infections. Eating yogurt is an ancient cure for vaginal infections and diarrhea.

The harmful bacteria that cause yeast infections are normally kept under control by the beneficial bacteria in our bodies. Antibiotics, antibacterial soaps, or a change in the body's acidic/alkaline balance, may wipe out beneficial as well as harmful bacteria, leaving the body open to infection.

Acidophilus creates beneficia bacteria. Yeast infection can be prevented or reversed by eating three servings of acidophilus yogurt daily or by taking acidophilus as a supplement.

L. acidophilus also produces lactase, the enzyme that breaks down milk sugar (lactose) into simple sugars. Fermented milks had been made since early times, when warm raw milk from cows, sheep, goats, camels, or horses was naturally preserved by common strains of Streptococcus and Lactobacillus bacteria. (The 'cultures' were obtained by including a small portion from the previous batch.)

These harmless lactic acid producers were effective in suppressing spoilage and pathogenic organisms, making it possible to preserve fresh milk for several days or weeks without refrigeration. Cultured products eventually became ethnic favourites and were introduced around the world as people migrated. Central to the production of cultured milk is the initial fermentation process, which involves the partial conversion of lactose (milk sugar) to lactic acid. Lactose conversion is accomplished by lactic-acid-producing Lactobacillus acidophilus.

University of Nebraska Cooperative Extension:

Yogurt is made by inoculating certain bacteria (starter culture), usually Lactobacillus acidophilus, or Streptococcus thermophilus and Lactobacillus bulgaricus, into milk. After inoculation, the milk is incubated at approximately 110°F ± 5°F until firm; the milk is coagulated by bacteria-produced lactic acid.

To maintain a culture, save a small portion of yogurt (1 c is enough for a 1-gal batch) to use as a starter culture for the next batch. Be sure to refrigerate the starter culture in a clean, air-tight container.

Accurate temperature control helps assure rapid coagulation and a good-tasting yogurt. A thermometer that measures temperature in the range of 90°F to 120°F should be adequate.

Yogurt can be made by using only nonfat dry milk (NFDM) and water, or by adding NFDM to skim milk, 2% milk, or regular milk. Nonfat dry milk is commonly available in two forms, instant and regular. Ideally, the milk powder should be weighed to obtain the desired solids content (15 percent on a weight basis).

Method for making yogurt:

Mix the appropriate quantities of liquid and dry ingredients.

Heat this milk in a saucepan or double boiler to boiling and cool immediately to 110°F. Discard any 'skin' that may have formed on the milk. Sugar may be added to the milk before boiling, if desired. Heating the milk to boiling kills any undesirable bacteria that might be pre-sent and also changes the properties of the milk protein so that it gives the yogurt a firmer body and texture.

To 1 gal of milk, add 1 cup of warm 110°F starter culture. Mix well but gently. Do not incorporate too much air. If too much air is mixed in, the starter culture will grow slowly.

Sanitize yogurt containers by rinsing with boiling water.

Pour milk into clean container(s) and cover with lid. If fruit is to be added to the yogurt, put in the bottom of the cup before adding the inoculated milk. The fruit should be at a temperature of 110°F. (Omit fruit from a small portion of the recipe and save it to use as a starter culture in the next batch.) Incubate filled containers at 110°F. Do not stir the yogurt during this period. There are several ways to control temperature during incubation:

Special yogurt-making equipment allows for careful temperature control without a thermometer and reduces the chances of failure.

Yogurt containers can be kept warm in a gas oven with pilot light and electric bulb, or an electric oven with light bulb of sufficient wattage (approximately 100 watts).

A Styrofoam box with light bulb may be used as an incubator.

Another good way to control temperature is to place yogurt containers into pans of 110°F water in an oven or an electric frying pan. Set oven temperature at lowest point to maintain water temperature at 110°F.

Wide-mouth thermos bottles, heating pads, and sunny windows also have been used.
Regardless of the method of temperature control used, determine ahead of time that the proper temperature can be maintained. To do this, place water or a container of water in the incubator and monitor its temperature with a thermometer.

Maintain 110°F temperature until the milk coagulates with a firm custard-like consistency (3-6 hrs). Check by gently tilting cup. Then refrigerate. It will keep for two to three weeks in the refrigerator.

Enjoy!

Trouble Shooting

Problem: Yogurt does not have a custard-like body but rather is soft and not smoothly solidified.
Causes:

Addition of starter culture to the milk before it has cooled down may kill the culture and prevent coagulation. Solution: Wait until the milk cools down to 110°F before noculating.

Both high and low incubation temperatures slow down culture growth and increase the amount of time necessary for coagulation. Solution: Use a thermometer to control temperature.

Extended storage of the starter culture reduces the number of live bacteria in the culture. Solution: Use more starter culture in the recipe or obtain a new culture.

Contamination of the culture with undesirable bacteria. Solution: Get a new culture. Also clean and sanitize yogurt containers each time yogurt is made.

Omitted or added an insufficient amount of nonfat dry milk to the milk. Solution: Accurately measure or weigh the nonfat dry milk.

Over-agitation before incubation may slow down starter activity. Solution: Combine starter culture and milk by mixing gently.

Problem: Yogurt tastes bad.
Causes:

Starter culture is contaminated. Solution: Obtain new culture.

Yogurt has over-set or incubated too long. Solution: Refrigerate yogurt immediately after a firm coagulum has formed.

Overheating of the milk causes an off-flavor. Solution: Do not overheat the milk.

Problem: Whey collects on the surface of the yogurt.
Causes:

Yogurt was over-set or incubated too long. Solution: Refrigerate yogurt immediately after a firm coagulum has formed.

Yogurt was bumped, moved or stirred during incubation. Solution: Place yogurt in a quiet location where it will not be disturbed.