Demystifying Yogurt

by Hal B. Klein

This exploration began two years ago when my friend Karen dared me to make my own yogurt. I like nerdy food projects, plus I assumed it would be totally easy. Imagine my shock when the yogurt didn’t come out as planned. It wasn’t terrible, but it wasn’t exceptionally pleasant, either. There was curd/whey separation, and the yogurt that remained was rather thin. I suppose that was to be expected since I used commercial yogurt as a starter culture, my oven’s pilot light as a heat source, and I was working on this project with decidedly limited (read: none) research. Fast forward to September, 2011. Armed with greater knowledge, freeze-dried active yogurt cultures, and a digital yogurt fermenter, I was ready to begin the challenge again. This time, I was determined to make something better than I could find at the supermarket.

Yogurt is milk that has been bacterially fermented. The two primary bacteria responsible for fermentation are Streptococcus thermophilus and Lactobacillus bulgaricus, although other bacterial cultures are often included either to enhance flavor or for perceived health benefits. The bacteria are temperature-sensitive; the best temperature for rate of growth depends on the specific bacterium, but they generally grow best between 110F to 113F. During fermentation, the bacteria convert lactose into lactic acid, which causes the milk to thicken, acidify, and change its flavor profile. The amount of thickening depends of the quantity of bacteria present, the fat content of the milk, and the time/temperature of the fermentation process.

The exact origins of yogurt are unknown, although evidence points to humans consuming fermented milk products for over 8,000 years. Yildiz believes, “The earliest yogurts were probably spontaneously fermented by wild bacteria living on the goat skin bags carried by nomadic people” (2). The spontaneous fermentation theory gives credence to the idea that yogurt doesn’t have a single point of origin, but instead developed in several warm-climate locales. James believes much of the credit for yogurt’s growth goes to the Armenians and Lebanese, “who have founded colonies in virtually every city of the the Western world” (32). A more widely accepted history, however, has nomadic Turks spreading yogurt to the Western World, most notably to the Balkans. According to Yildiz, the first written descriptions of yogurt were recorded in 1070 AD. Yogurt was fermented commercially by Danone in 1922, and “particularly since 1950, the technology of yogurt and understanding of its properties have advanced rapidly” (Prajapati and Nair 7).

One of the primary reasons people consume yogurt is for its health benefits, either real or perceived. The consumption of yogurt for health-related reasons isn’t a modern conceit, either. “Ancient physicians of the Near and Middle East prescribed yogurt or related soured milks for curing disorders of the stomach, intestines, and liver and for stimulation of the appetite” (Prajapati and Nair 7). Contemporary research demonstrates that yogurt can be a functional food for people with lactose intolerance. Milk is widely regarded as highly nutritious, yet milk in unfermented form is not well-tolerated by many people. The bacterial fermentation that takes place converts “lactose, the milk sugar that so many humans cannot tolerate, into easier-to-digest lactic acid” (Katz 6). It should be noted that although fermentation improves tolerance to milk products in many people, it is not universal and some people will still experience discomfort regardless. Probiotics, defined by the National Center for Complementary and Alternative Medicine as, “live microorganisms (in most cases, bacteria) that are similar to beneficial microorganisms found in the human gut…also called ‘friendly bacteria’ or ‘good bacteria’…” is another reason people consume yogurt. Although there is conflicting evidence regarding the efficacy of consumed probiotics, Lactobacillus acidophilus and Bifdobacterium spp. have been shown to have at least some therapeutic value (Shah; Chandan & Shah).

Nearly all of the yogurt in the market today has been mass-produced using milk from industrially raised dairy cows. The yogurt is almost entirely sold pre-sweetened, and as Mendelson characterizes, with “lunatic results.” She elaborates:

You can now walk into thousands of supermarkets and take your pick of ‘amaretto cheesecake’ or ‘lemon cream pie nonfat yogurt’; low-fat yogurt with a choice of chocolate chips, granola, or Reese’s Pieces as a topping…without necessarily being able to find any item that people brought up on the real thing would recognize as plain yogurt worth putting a spoon into (28).

This isn’t to say that high-quality, commercially made, yogurt from sustainable sources can’t be found at the supermarket; it can be, and it certainly can be found at co-ops and farmers’ markets throughout the United States. Still, it was more motivation for me to try my hand at making yogurt again.

I began my 2011 yogurt-making project by purchasing a EuroCuisine YMX650 Digital Yogurt Maker. Organic yogurt retails for anywhere between $0.11 and $0.26 per ounce, making it fairly more expensive than organic whole milk[1], the only ingredient of significant cost in making yogurt. I figured my investment would be paid back fairly quickly. Of course, this would also require me eating considerably more yogurt than I normally do. That’s okay. All in the name of science, right? In order to maintain the integrity of my experiment, I decided to use the same milk processor for all the batches. I used Natural by Nature brand whole milk from grass-fed cows. It should be noted that yogurt can be made from lower fat or soy milks, but the yogurt will be thinner, and you need to allow it more time to ferment.

My first batch of yogurt was made from the starter packet of culture (L. bulcaricus, L. Acidophilus, S. thermophilus) included with the yogurt maker. I was instructed to scald whole milk to 180F[2], rapidly cool the milk to 110F, and add the culture. I did as instructed, trying to take the temperature as precisely as possible. Once mixed, I poured the inoculated milk into seven 6oz. containers, and set the timer on the yogurt maker for seven hours. The instructions said it was crucial not to disturb the machine, but, after 3 hours, I couldn’t resist. I peered in, shaking one of the containers ever-so-gently. It looked like…warm milk. I replaced the lid, and vowed not to mess with the machine anymore. Let the bacteria do their work. A watched pot never ferments, isn’t that the old saying? However, I couldn’t contain my curiosity, and I checked it again an hour later. No change. After 7 hours, the milk looked slightly, vaguely yogurt-like, but it appeared more like the early stages of cheese making. There were tiny curds.

I refrigerated the yogurt overnight and tasted it first thing in the morning. It was…well…it wasn’t much better than my previous yogurt-making experiment. Thin, sour, with a slight off-taste. Edible, to be sure, but certainly not more delicious than a quality store-bought yogurt.

I wasn’t ready to give up. Round two was a simultaneous fermentation project. Into the yogurt maker went an heirloom Bulgarian starter culture containing L. Bulgaricum and S. Thermophilus bacteria. At the same time, I started a Finnish heirloom culture called Villi, which contained Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis biovar. diacetylactis, and Leuconostoc mesenteroides subsp. cremoris.  Both cultures required first activating the starter and then making a batch of yogurt from that starter. After the initial batch, full batches could be made by taking some of the existing yogurt and mixing it into milk that would ferment into the next batch.

I began the Bulgarian culture by scalding/cooling the milk, stirring in ½ teaspoon of the starter, and placing it in the yogurt maker. After eight hours in the fermenter, there was no change! What I had was warm milk that smelled slightly of cheese. I thought about throwing it out, but then decided to give it another few hours. After twelve hours, there was something thicker, but it was also chunky.

I thought I might as well refrigerate it. The starter looked a little better in the morning, so I began a full batch of yogurt. After fermenting eight hours (no peeking this time), I put the warm yogurt into the refrigerator and let it rest until morning. The next day, I was pleased to discover something that actually resembled yogurt. Okay, there were still a few sizeable chunks in it (concentrated bacteria colonies, perhaps?), but the flavor was tart, clean, and pleasant. I mashed a half-pint of blueberries, added elderberry syrup, and stirred in six ounces of the yogurt. Delightful!

The Villi proved an even greater test of patience. This culture is meant to ferment at room temperature. I brought a half-cup of milk to room temperature and added a ½ teaspoon of the starter culture. I placed it somewhere fairly warm, which proved tricky, as it was a hot summer day, and my air conditioner was working overtime. Twenty-four hours later, nothing. Nothing at all. I took the temperature of the culture—it was only 69F. How was it colder than the room? I wrapped it in a hand-towel like it was a baby in need of nurturing, and moved it to a different location. Twelve hours later, still nothing. This was disturbing. It wasn’t supposed to take this long. And I wasn’t supposed to care this much. I microwaved my petulant starter for 10 seconds, and the temperature now registered eighty-two degrees. It instantly grew thicker. Good. This time, I left it nestled between my cable box and my television. This was visually awkward, but at least it provided some protection from the hard-working air conditioner.

Eight hours later, success! It looked like a cultured starter. I was ready to incorporate the culture into four cups of milk. I decided not to mess with a good thing, and returned the food-grade plastic jug to its cozy spot near the television. I let the yogurt ferment for 18 hours and checked in again. It smelled of cheese and had a crust on the top. Determined to let things be, I simply placed it in the fridge. The next morning, the crust had dissipated a little bit, and the odor was milder than it had been the night before. I sampled the yogurt, and, to my surprised delight, it was rather delicious! This is a very thin yogurt, so I decided to juice a few peaches, mix with the yogurt, and have a fantastic, cool summer yogurt drink.

After all that, I asked myself, “Is it worth it? Should I continue to make yogurt at home?” I was still on the fence, but leaning toward yes—so I experimented with a few more batches. With practice, my homemade yogurt tasted much better–more complex, and cleaner, if you will–than commercial yogurt. Plus I had the power to decide where the milk is sourced. It’s also more economical than buying it at the grocery store. However, I also became a slave to my yogurt maker. For awhile I had three different yogurt cultures alive in my refrigerator, and I needed to propagate each of them every 7-10 days or else they would die. That’s a lot of responsibility.

Postscript

They all died.

The EuroCuisine went first, because it was the least delicious. The Finni lasted several more batches and was the foundation for many delicious yogurt-based fruit drinks (try adding a little bit of basil). But eventually I had to let it go–there was still too much yogurt in the fridge. The Bulgarian culture lasted the longest; I kept it alive for nearly two months. Sadly, all yogurt cultures eventually burn out (OK, truth is they eventually get overrun by other wee critters, but I’m sure you’ve heard enough about microbiology already…) and so I had to let it go.

I was travelling fairly frequently for a few months, and, because of that, the yogurt making basically stopped. Happily, after having a cup of terrible store-bought yogurt (fake honey flavoring…really?) six weeks ago, my interest has been renewed, and the Streptococcus thermophilus and Lactobacillus bulgaricus bacterias are again alive and kicking in my kitchen. The results have been pretty delightful. My most recent discoveries: Letting the milk scald for 15-20 minutes vastly improves the texture (the extra time at high heat changes the protein structure of the milk), and adding 2 tablespoons sugar before fermentation creates a more complex flavor profile for the yogurt.

Try making yogurt yourself. If you don’t have a yogurt maker I’ve been told a slow-cooker set on its lowest setting works just fine. Or you can just awkwardly wedge a batch behind your television like I did.

Works Cited:

Chandan, Ramesh C., and Nagendra P. Shah. “Functional Foods and Disease Prevention.” Manufacturing Yogurt and Fermented Milks. Ed. Ramesh C. Chandan. Ames, IA: Blackwell Pub., 2006. 311-25. Print.

James, Frances. “Yogurt: Its Life and Culture.” Expedition 18.1 (1975): 32-38. Print.

Katz, Sandor Ellix. Wild Fermentation: the Flavor, Nutrition, and Craft of Live-culture Foods. White River Junction, VT: Chelsea Green Pub., 2003. Print.

Mendelson, Anne. Milk: the Surprising Story of Milk through the Ages : with 120 Adventurous Recipes That Explore the Riches of Our First Food. New York: Alfred A. Knopf, 2008. Print.

Nummer, Brian A. “Fermenting Yogurt at Home.” University of Georgia. National Center for Home Food Preservation | NCHFP Publications, Oct. 2002. Web. 26 July 2011..

Prajapati, Jashbhai B., and Baboo M. Nair. “The History of Fermented Foods.” Handbook of Fermented Functional Foods. Ed. Edward R. Farnworth. Boca Raton: CRC, 2008. 1-9. Print.

“Probiotics [NCCAM Health Information].” National Center for Complementary and Alternative Medicine [NCCAM] – Nccam.nih.gov Home Page. Web. 30 July 2011. <http://nccam.nih.gov/health/probiotics/>.

Shah, Nagendra P. “Probiotics and Fermented Milks.” Manufacturing Yogurt and Fermented Milks. Ed. Ramesh C. Chandan. Ames, IA: Blackwell Pub., 2006. 341-54. Print.

Yildiz, Fatih. Development and Manufacture of Yogurt and Other Functional Dairy Products. Boca Raton, FL: CRC/Taylor & Francis, 2010. Print.