- Milk, dry milk, yogurt
- Jars, thermometer, measuring cup, saucepan, cooler
To begin, you need to mix some milk along with some nonfat dry milk powder. You can simply mix the two ingredients together in the saucepan that you will use to heat the milk. We used regular dry milk, but you can substitute instant but you will need twice the amount listed below. The ratio of milk to milk powder is determined by the type of milk you are using:
- 1 qt. (1L) nonfat milk + 1/2 cup (120mL) powder
- 1 qt. (1L) lowfat milk + 1/3 cup (90mL) powder
- 1 qt. (1L) whole milk + 1/4 cup (60mL) powder
Stir the ingredients together and gently stir over medium to high heat. Note that you can add sugar or honey at this stage if desired. Heat the milk to kill any bacteria: about 175°F (80°C). Immediately remove the saucepan from heat and set aside to cool. Note that overheating the milk beyond 175°F (80°C) may cause an unpleasant flavor.
While the milk is cooling you need to ‘sterilize’ any containers or utensils that will touch the milk/yogurt. The addition of unwanted bacteria can inhibit the coagulation of the yogurt, so this is an important step. Simply boil some water (we used a pressure cooker) and rinse all items that you will be using. We simply placed all the items in a sink and slowly poured the hot water over all the surfaces.
To speed up the cooling of the milk, you can gently pour the milk from the saucepan into a sterilized container, cover it, and put it in the refrigerator or freezer. Regardless of how you are cooling the milk, monitor the temperature with a thermometer, until it reaches 110°F (44°C). Note that some glass thermometers cannot handle high heats and may break. A kitchen thermometer like the one shown on the right is most suited for this.
Once the critical temperature has been reached (this can take about 30 minutes) you are ready to add the yogurt starter culture; remember that you must use a yogurt with active or live cultures for this to work (a previous batch is perfect). You need about 1/4 cup (60mL) of starter culture for each quart (liter) of milk. You should warm the starter culture to 100 degrees F (44 Celsius) before incorporating it into the milk. Using the microwave is fine, but do not overheat the yogurt because you may kill the culture. When the appropriate temperature has been achieved (usually less than 30 seconds) gently stir it into the milk using a sterilized utensil. Thorough mixing is important but do not incorporate too much air into the liquid.
The final step is to incubate the liquid for approximately three to six hours at 110°F (44 Celsius) plus or minus 5°F (3°C). We recommend using glass jars with lids for the yogurt, but lidded plastic will also work. There are many ways to achieve the stable temperature that is required but we have found that a cooler filled with the proper temperature water is a very easy solution. The water level should be kept below the tops of the containers to ensure that they don’t start floating around. You should have all of this this prepared in advance so you can place the jars in right after mixing.
Monitor the temperature so that it doesn’t drop more than 5°F (3°C) in relation to the target temperature; to do so you can simply add hot water as necessary. If you put the cooler in a warm place, you may only have to monitor the temperature once every hour or two. Do not disturb the yogurt during this period. After about three hours but maybe as long as six, the culture will spread throughout the liquid and the yogurt will coagulate. Note that some water (whey) may collect at the top. On occasion, gently tip the jar(s) to test and once the yogurt has coagulated, remove it from the incubator and refrigerate. Congratulations, you’ve made your own delicious yogurt, and it will last for about two or three weeks if properly refrigerated.
Click here for detailed procedure of Method #3
source: source: dost.gov.ph, uniqueprojects.com, photo from www.latteria-vipiteno.it