There are several reasons to love yogurt. First, it’s a product of microbes. If that’s not enough to make you appreciate microbes, consider the role of microbes in wine, cheese, beer, and other tasty treats. Second, it’s delicious and nutritious. Yogurt and a bit of cereal make for a quick and easy breakfast, and is usually cheap enough for the starving grad student (if you buy it on sale.) Unfortunately, a lot of the yogurt that goes on sale is a bit too sweet to eat for breakfast and would make a better dessert. Fortunately, yogurt is really easy to make, and you don’t need fancy equipment to make it. If you’re concerned about artificial ingredients to the point of dissing science in your yogurt caps like Chobani famously did, then it’s best to just make it yourself. Don’t know how? It’s actually really easy, and one of the more enjoyable experiments taught in some introductory microbial sciences class (so stop hating on science, m’kay?).
What you’ll need: Milk, a bit of yogurt (as a starter culture), an appreciation for the awesomeness that is microbiology
Boil the milk in a pot–be careful because milk burns easily, so stir frequently. This step is necessary because even pasteurized milk can still contain nasty bacteria. Some people like to add evaporated milk to the milk, to ensure the yogurt microbes have an excellent growing medium, but it’s not really necessary (though it helps if you are trying to use skim milk or 1% fat milk).
Once boiled, cover and remove from heat. Allow the milk to cool to about 40 degrees Celsius. If you don’t have a thermometer, it’s generally when you can touch the pot without burning yourself, but it still feels a uncomfortably hot. If you want to be sure to get it right, use a thermometer. While you wait for the milk to cool to the right temperature, turn on your oven on for a little bit to get it toasty in there, but not too hot. When your milk has cooled to the right temperature, mix your starting culture in, cover, and place in the oven. The oven will serve as an incubator to ensure that the milk does not cool too quickly, so be sure that it’s not too hot in your oven, else you will cook your microbes. One of the more common strains of bacteria used in yogurt production is Streptococcus thermophilus which (as the ‘thermophilus’ in its name implies), grows optimally at warmer temperatures, so turn on the oven briefly if it begins to start cooling. The other species of bacteria commonly used in yogurt production is Lactobacillus delbrueckii subsp. bulgaricus which produces the amino acids from milk proteins which are then used by s. thermophilus.
Let the microbes do their thing for a couple of hours. You can be as involved as you want with them (ie- checking oven temp. frequently to ensure optimal temperatures.) or you can leave it in the oven overnight after insulating the pot. Stick in the refrigerator for a couple of hours the next morning and it’s ready to eat. If you like your yogurt thicker, you can strain out some of the whey by putting some in a coffee filter in a large bowl or plate and leaving it in the fridge.
Flavor it however you like, or enjoy it plain for a super cheap breakfast. 1 gallon of milk will make 1 gallon of yogurt (assuming you don’t strain out the whey), so your home made yogurt will cost about $3/128 oz compared to $0.50/8 oz. If you do strain your yogurt, you can expect to get about 1/2 as much, so it’s about $3/64 oz of strained (greek) yogurt compared to about $1/6 oz.