Stories from the Lab: Fun with Yogurt

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Hello, fellow food lovers! Welcome back to my culinary science blog. If you’ve read some of my previous “Stories from the Lab” posts, you’re aware of the thrilling projects my classmates and I have been doing. This time, in my Microbiology class with Professor Monaghan, we made different varieties of yogurt.

Have you ever made homemade cultured yogurt? Let me tell you, it’s exciting! It’s a process that involves curdling milk and fermenting it into a semisolid tart mass. While it takes a while to complete, the end result left our class oohing and aahing.

Yogurt manufacturing is a multi-billion-dollar industry. If done properly, you can make it at home. Yogurt is originally a Turkish root word that means thick. It involves two kinds of bacteria:  Lactobacillus delbrueckii and Streptococcus salivarius subspecies thermophilus. Both of these bacteria stimulate the growth of each other, and combining the two helps acidify the milk. When the milk is left out, fat-enriched cream forms at the top. The remaining milk can naturally turn into acid and curdles into thick yogurt.

In the lab, my classmates and I made yogurt with several different types of milk, including Soy milk, coconut milk, whole milk, almond milk, and oat milk. My teammate and I got to use oat milk, which has become an early food trend of 2019.

It’s dairy-free and nut-free and contains more protein and fiber than many other types of milk. Major manufacturing companies like Oatly, Starbucks, and Quaker have utilized oat milk in beverages and on their restaurant and company menus.

Time to Make the Yogurt!

Yogurt-making involves two steps: heating the milk and fermenting the warm milk. With the oat milk, I heated it to 110 degrees F in a pot and then mixed in a yogurt culturing packet. The yogurt starter packet I used was by a brand named Culture for Health. This—along with the fact that I used oat milk instead of traditional whole milk—made the yogurt completely vegan. Usually, this heating process allows the dairy milk to denature its protein structure so it can properly thicken when it meets the bacteria. In non-dairy milk, it helps activate the starch. The milk is then cooled so the bacteria can grow when added.

After heating, we transferred the mixture to a culturing container jar. Before closing, we lined the top opening with cheesecloth. The jars were then added to a thermal circulator until the next day.

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Fermenting the milk allows the yogurt to come to the correct consistency while it sets. At 108 to 110 degrees F, the yogurt bacteria tend to produce lactic acid and the milk proteins start to gel. Usually, this part of the process can take anywhere from 2 to 8 hours, or even overnight. We left the yogurt in the thermal circulators overnight. The next day, we transferred the yogurt to our walk-in refrigeration and held it for the next week.

After the first two hours, some of yogurt samples began to separate immediately. Our oat milk sample was one of them.

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Initially, Professor Monaghan said that was a clear sign that the oat milk was not going to work, but as it turned out, it did—and was actually quite sweet-smelling. It had a smooth texture but was somewhat thin.

The Results

After one week, my classmates and I were thrilled to look at and taste our yogurt samples. We had made 10 different samples, but only four of them cultured properly. The samples that worked were the traditional, oat, soy, and Bulgarian yogurt. Bulgarian yogurt is one of the most popular variations you’ll find. It usually is thick and creamy, and smooth. One of the yogurt samples that did not work out was the coconut milk sample. It actually grew a type of fungus on the surface—which our professor said we were absolutely not allowed to taste.

According to Professor Monaghan, the soy yogurt properly cultured because the soy milk sample had enough fat and protein so that when they started to curdle, they were able to emulsify and form a set structure. The traditional milk sample also had enough fat in it to set the structure. My classmates agreed that this was best out of all the samples made.

As you can see, making yogurt with different kinds of milk generates different results. I had never made yogurt before this, so the results really astonished me. Some of the milk produced thick yogurt, while others produced much thinner yogurt.

Be sure to catch my next blog, when I add the Bulgarian yogurt sample to agar to examine the bacteria that grows on it. Until next time, stay “sciencey” and keeping loving food!

By Majestic Bryant-Lewis

Majestic Lewis-Bryant