Yogurt

When I first heard that yogurt could be made at home without any special equipment, I was intrigued. 

People make homemade yogurt for a variety of reasons, cost and taste being the most common. For me however, it was the fact that 4 years of post-secondary education, 6 years of graduate school, and even more time spent working in a research lab, were finally going to be useful.

To describe it in lab terms, yogurt is bacterial culture. Bacteria are used to inoculate or seed a liquid medium, in this case, milk. As the bacteria grow, they convert the lactose in milk to lactic acid, which gives yogurt its characteristic “tangy” flavor. The lactic acid also interacts with the milk proteins to produce a thicker texture.

There are a couple of things to consider when making yogurt:

1. Milk.

Whole milk gives the best results when making yogurt. If you want something lower fat, 2% milk with added milk powder, to increase the protein concentration also works really well. Here in Texas, I’ve had great results using the high-protein 2% milk from Borden.

2. Bacterial starter.

While you can buy freeze-dried bacteria cultures, it’s much easier to go to the grocery store and buy a small container of yogurt to use as your starter. Different yogurts produce subtly different flavours and textures. I quite like Activia yogurt by Dannon, mostly because it produces a smooth-textured yogurt, but also because I get a kick out of culturing their proprietary bacterium, Bifidobacterium lactis DN-173 010. 

3. Yogurt style

The method and length of the incubation period gives different styles of yogurt. The best and quickest way is to use something to keep your yogurt at the ideal incubation temperature of ~120°F/50°C with an electric yogurt maker. However, wrapping the yogurt in a towel and storing it in a warm spot works just as well, if not a bit slower. I’ve found that the towel-method and the following incubation times work well:

4 hours: very soft, drinkable yogurt

6-8 hours: very soft, cream like, no tang

9-10 hours: firm, slight tang.

While most recipes suggest reserving a bit of your homemade yogurt to start the next batch, I never do.  For consistent results, so I always use store-bought yogurt when making a new batch.

Of course, no bacterial work can be done without adhering to safe food handling practices, or as we say at work, aseptic technique. In the lab, we autoclave our dishes, wear gloves, disinfect surfaces with ethanol, and even control the air flow. For yogurt, just wash everything in really hot water. The sanitize cycle on a dishwasher is convenient. If you want to be extra-cautious, boil your jars and utensils as though you were canning.

Yogurt

Adapted from Bon Appetit

8 cups of whole milk

6 tablespoons of yogurt with live and active cultures (or 1 single serving pack of Activia)

Kitchen thermometer

1. Heat milk in a medium, thick-bottomed, saucepan over medium-low heat, stirring and scraping the bottom of the pan often with a heatproof spatula. If you have a thin-bottomed saucepan like I do, just accept the fact that some of the milk may scorch.  Heat until the milk just until it begins to bubble, around 185°F /85°C. If you are using raw milk, this step will kill off any bacteria, so that it’s a clean slate for your culture. 

2. Turn heat to low and keep milk at 185°F /85°C for about 20-25 minutes. This long heating period denatures the milk proteins, so that it thickens properly rather than forming cheese.

3. Turn off the heat and let the milk cool to 110°F-130°F /40°C-55°C. You can put the saucepan in a large bowl filled with ice water to speed things up. A skin will form over the milk as it cools. It’s edible, but I scoop it out and discard it.

4. Using a sterile spoon, place your yogurt in a small, sterile bowl and slowly stir in about 1.5 cups of warm milk until it is completely incorporated.  You want the dilute the yogurt so that it has the same consistency as milk.

5. Pour the yogurt mixture into the remainder of the milk in the saucepan. Gently stir the milk until everything is mixed.

6. Pour the yogurt mixture into glass or plastic jars with lids. I use a mixture of small canning jars and old jam/sauce jars. Wrap the jars in a bath towel and place in a warm oven (just make sure you turn off the heat after the yogurt goes in) or another warm spot. Let the mixture incubate from 4-20 hours, depending on the desired result. The longer you incubate the yogurt, the thicker and tangier it will be.

7. Place yogurt in the fridge for several hours to stop the bacterial growth and to firm up the yogurt. A little bit of whey may form on top, which can be stirred back into the yogurt or poured off.

8. For thicker yogurts, simply strain after chilling.  For Greek yogurt, strain the yogurt for several hours. For labneh, strain overnight. While I prefer unsweetened yogurt, toppings that I’ve enjoyed include honey, fruit, pumpkin butter and black sesame powder.