I remember being introduced to making yogurt in science class. That experiment involved tin foil, a shoebox, a 60watt light bulb, a few jars, and a thermometer. Years later I am still making yogurt at home albeit with tools more commonly found in the modern kitchen. I have tried several different methods of heating, cooling, and fermenting yogurt over the years. I will explorer these methods below starting with the simplest and getting more technical, using equipment more common to gastronomy than home cooking.
A few words on Sanitation
Proper sanitation is very important! Yogurt is a fermented food. This means that the process of making yogurt involves creating an environment that is ideal for bacterial growth. Bacteria are opportunistic bastards and don’t care about your intentions to stay healthy. Any bacteria present or introduced in this process are likely to grow and some of them can make you very ill.
To prevent illness and foul batches of yogurt ALL equipment and utensils that come in contact with the yogurt during the process must be clean and sanitary. I recommend using stainless steel or non-porous equipment and utensils and avoiding wood or plastics. Items can be sanitized with a solution of 1 ounce bleach to 1 gallon water. Let the items soak in this solution for 10 minutes to kill off any bacteria that maybe present. If you have a dishwasher with a NSF certified sanitation cycle this is a good alternative to using a bleach solution. Finally, if bleach is not appealing and or you do not have a NSF certified dishwasher a commercial sanitation solution works as well. After making sure that all equipment and utensils are clean I use STAR SAN commercial sanitizer. A bottle of STARSAN can be purchased at most home brew shops and websites selling home brewing supplies. It is inexpensive, easy to use, and an 8 ounce bottle, used as directed, will yield 40 gallons of solution.
Any utensils that have come in contact with the yogurt should be washed and resanitized before being used again with the batch. A spoon or thermometer laying on the counter with milk or yogurt on it is inviting to all types of bacteria. Putting that utensil back in contact with the milk or yogurt is asking for trouble.
Finally if it doesn’t smell right, or taste right something may have gone wrong and its best to throw it out. If it doesn’t look right, has changed colors, consistency that isn’t creamy or milky throw it out.
With sanitation covered its time to get to the fun stuff. My normal batch starts with between half a gallon to a gallon of whole milk. Lower fat milk can be used but will result in a thinner yogurt. This method uses a double boiler to heat the milk. A double boiler (if you don’t already have one) can be made by finding a bowl that will both hold the milk and will fit in pan with water underneath it. I use a stand mixer bowl in a 2 quart pan.
After sanitation temperature is the next most important factor in making yogurt. The milk gets heated to 180 degrees. If it goes too far over 180F the proteins, in the milk, over develop and yogurt will not ferment properly. Ultra-pasteurized milk will not work for making because it is heated past 180F in the ultra-pasteurization process. You will have something closer to ricotta cheese, after draining the excess liquid off. If the milk doesn’t get to 180 then the proteins do develop enough and the milk may also have other bacteria in it that isn’t killed off. An accurate instant read thermometer is needed. If you don’t already own one, you should purchase one before attempting to make yogurt.
Instant read thermometer
Large bowl, large enough for the top of the double boiler to fit in
Stainless steel spoon
Stainless steel whisk
2 quarts of whole milk
1 single serving container of unflavored yogurt
Pour the milk in to the double boiler and place it on the stove over medium heat. Once the water in the bottom of the double boiler starts to simmer stir the milk and check the temperature. Watch the temperature of the milk until it reaches 180F. Once the milk reaches 180F turn off the heat and very carefully remove the bowl from the double boiler. Turn oven on to keep warm. Fill the larger bowl with cold water in the sink. Carefully place the large bowl of hot milk in the cold water. Stir the hot milk with the spoon to help it cool off. Keep stirring until the instant read thermometer reads 105-110F. If possible keep cold water running in to the bowl without getting water into the hot milk. Remove bowl of now warm milk and place on counter top. Open the single serve yogurt. Whisk the yogurt in to the warm milk. The milk now has an ample supply of yogurt bacteria and is ready for fermentation. Turn off the oven and place the mixture in the warm oven. Let the mixture sit in the oven for 6 to 12 hours. The longer it sits the thicker and more flavorful the yogurt will get. Once the yogurt has reached its desired flavor or consistency it is ready for the refrigerator.
Greek yogurt is made by straining the liquid off of fresh yogurt. Place a bowl under a strainer large enough to hold all of the yogurt you want to strain. Place a few layers of cheese cloth in the strainer and gently fill it with yogurt. Cover the strainer with plastic wrap. Place the bowl with strainer in the refrigerator. After 12 hours check it for consistency and discard any liquid that has collected in the bowl. If the greek yogurt is at a consistency you like you can pull it out of the strainer by lifting the cheese cloth. Place the fresh greek yogurt in a clean container and refrigerate. If you want thicker greek yogurt leave it in the strainer until it is at a consistency you enjoy. Use within two weeks
Advanced (other methods)
These methods don’t make it any more difficult but they do use equipment not found in the average kitchen. In fact I think these methods make it easier, the hard part maybe finding space for extra cooking gear in the kitchen.
Using an induction cook top
I have really enjoyed using a single burner induction cook top for many heating tasks in the kitchen. The cook top I have has temperature settings from 100F to 380F. Using the induction cook top for making yogurt I don’t need to use a double boiler. I pour all of the milk in to an induction ready pot and set the cook top to 160F and let it heat. When it reaches the set temperature a relay will start clicking on and off as it regulates the temperature of the pot. When I hear the clicking its time to turn up the temperature, grab my thermometer, and start stirring. The induction heats the pan at the bottom and stirring help distribute the heat through the pot.
I can easily cool the whole pot by placing it in a larger pot with cold water. Once it has cooled back down to the 105-110 range then I whisk yogurt into the warm milk. I can place the whole pot back on the induction cook top and set it for 100F for 8hrs. The cook top will do the rest. Using this method I have made 1 gallon batches.
Using Sous Vide
This uses a sous vide water circulator for heat. This isn’t actually sous vide I am not putting the milk under vacuum. The milk gets divided up in to quart mason jars with at least an inch of head space. The lids are placed on the jars. The jars are then carefully placed in a water bath. I set the sous vide circulator at 183F for 8 hours. It takes a long time to heat a quart jar filled with milk. The good news is I don’t have to watch it the whole time. After 8 hours I pull the jars out and make sure the lids are tight. Glass jars do not like large temperature differences do not place them in cold water. I let them sit on the counter top to cool off. The jars are sealed and they have been in the water bath long enough to kill anything that could possibly have gotten in to them. I am not overly worried at this point. Once the jars are cooled I divide up the yogurt and mix it into the individual jars. The lids go back on and they go back into the water bath. This time the temperature is set to 105F for 12 hours. At the end of the 12 hour fermentation the jars are placed in the refrigerator.