January's Au Lait du Mois: Yogurt

As I mentioned previously, co-blogger Rebecca gave me Ricki Carroll's Gourmet Home Dairy Kit for Hanukkah/Christmas/Solstice/Kwanzaa/New Year 2010. My goal this year is to post once a month about my experience making either a soft fresh cheese or another dairy treat with the Gourmet Home Dairy Kit. Rebecca has gamely agreed to post her experiences too, as she has a Kit of her own. I'm starting with yogurt as I am already somewhat familiar with the process.

Many moons ago I posted about Jennifer Reese's piece for Slate comparing the wonders of homemade versus store bought foodstuffs including yogurt, which provided both a price comparison and a taste comparison, as well as links to recipes. She comes down heavily on the side of making your own yogurt. Reese's section on yogurt is a must read.

I made my first yogurt about five months ago following the instructions put forth by Ruth Yaron in Super Baby Food. Here is my Southern California Summertime version of yogurt adapted from Super Baby Food.
Ingredients:

• 2 qt. raw milk
  
• 1 container Stonyfield Farm Oikos organic, 0% fat, Greek yogurt

Implements:

• 2 qt. glass jar
  
• Pot that glass jar can fit into and be 2/3s covered in water.
  
• Dairy Thermometer
  
• Spoon
  
• Plastic wrap
  
• Rubber band
  
• Measuring spoons
  
• A small bowl

Procedure:

• Strain milk through sieve into a 2 qt. glass jar.
  
• Put the jar into a pot of boiling water for 10 minutes.
  
• While milk is boiling, take Oikos out of fridge.
  
• After milk has boiled for 10 minutes, take the jar out of the pot and put thermometer in the milk. Cover the top with plastic wrap secured with a rubber band. Put the jar in the fridge.
  
  
• When the milk's temperature gets down to 112 F (to go from 200 to 115 degrees it takes about 1 hr. 45 min. in the fridge), add 1 T Oikos per 2 C of milk. Take a little of the milk, mix it with the yogurt in a bowl, then stir it gently into the milk.
  
• Put the thermometer in the milk and recover the top with plastic wrap secured with a rubber band. Place the yogurt in the sunniest spot on the back porch and check occasionally that the milk's temperature doesn't dip below 90 degrees. If it gets close to 90, put the jar in a pot of water on the stove to warm, but not above 120 F.
  
• After 6 hours, start checking hourly for doneness by touching the top with your clean finger. It should have a thick pudding-like consistency.
  
• When it is at the correct consistency, put the jar in the freezer for 10 minutes, then put it in the fridge.

Ricki Carroll's Gourmet Home Dairy Kit has one definite advantage over the Super Baby Food method: the Yogotherm yogurt incubator allows you to do this in places other than Southern California on a summer day. Also, the dairy thermometer that comes in the kit ROCKS! So much better than my all-purpose instant-read thermometer.

Other than slight modifications in the yogurt making process, the other big difference (so long as we're all using cow's milk) is the cultures. Harold McGee's On Food and Cooking: The Science and Lore of the Kitchen gets into quite a bit of detail on the exciting bacteria in fermented milk products.

Early in the 20th century, the Russian Nobelist Ilya Metchnikov (who discovered that white blood cells fight bacterial infection) gave a scientific rationale to [the belief that yogurt and other cultured milks can actively promote good health], when he proposed that lactic acid bacteria in fermented milks eliminate toxic microbes in our digestive system that otherwise shorten our lives. Hence Dr. James Empringham's charming title of 1926: Intestinal Gardening for the Prolongation of Youth.

Metchnikov was prescient. Research over the last couple of decades has established that certain lactic acid bacteria, the Bifidobacteria, are fostered by breast milk, do colonize the infant intestine, and help keep it healthy by acidifying it and by producing various antibacterial substances. Once we're weaned onto a mixed diet, the Bifidobacterial majority in the intestine recedes in favor of a mixed population of Streptococcus, Staphylococcus, E. coli, and yeasts. The standard industrial yogurt and buttermilk bactera are specialized to grow well in milk and can't survive inside the human body. But other bacteria found in traditional, spontaneously fermented milks--Lactobacillus fermentum, L. casei, and L. brevis, for example--as well as L. plantarum from pickled vegetables, and the intestinal native L. acidophilus, do take up residence in us. Particular strains of these bacteria variously adhere to and sheild the intestinal wall, secrete antibacterial compounds, boost the body's immune response to particular disease microbes, dismantle cholesterol and cholesterol-consuming bile acids, and reduce the production of potential carcinogens.

McGee laments the industrialization of yogurt production to the extent that it has reduced the commonly used bacteria to two: Lactobacillus delbrueckii subspecies bulgaricus, and Streptococcus salivarius subspecies thermophilus. Oikos, which I used as my starter in the recipe above, contains five live active cultures: the two common industrial yogurt bacteria--L. bulgaricus and S. thermophilus--two found in traditional, spontaneously fermented milks--L. casei and L. acidophilus--as well as Bifidobacteria. Ricki's Yogurt (Y4) Tangy culture which came in the kit says it contains "s.thermophilus, l. delbrueckii, s.bulgaricus, s.lactis." This labeling might include a typo. Lactobacillus delbrueckii subsp. bulgaricus is one bacterium, not two. Ricki also sells two other yogurt cultures. The following table shows which yogurt or yogurt cultures contain the six bacteria I found.

	Streptococcus salivarius subspecies Thermophilus	Lactobacillus delbrueckii subspecies bulgaricus	Lactobacillus acidophilus	Lactobacillus casei	Bifidobacterium	Lactococcus lactis
Oikos	Yes	Yes	Yes	Yes	Yes
Ricki's Y4	Yes	Yes				Yes
Ricki's DS	Yes	Yes	Yes		Yes
Ricki's Bulgarian	Yes	Yes
Trader Joe's European Style Organic Whole Milk Yogurt	Yes	Yes	Yes		Yes

I modified Ricki's instructions slightly based on my reading of On Food and Cooking. As McGee explains, there are basically two steps to yogurt making: heating the milk and fermentation.

Ricki has you heat the milk to 185 F and then let it stand for 10 minutes. She specifically tells you NOT to boil the milk. So she would disapprove of my previous yogurt making practice. I originally boiled my milk for 10 minutes because that is how Super Baby Food suggests one pasteurize raw milk prior to making it into yogurt. McGee explains that heating the milk to 185 degrees for 30 minutes or 195 degrees for 10 minutes improves

the consistency of the yogurt by denaturing the whey protein lactoglobulin, whose otherwise unreactive molecules then participate by clustering on the surfaces of the casein particles. With the helpful interference of lactoglobulins, the casein particles can only bond to each other at a few spots, and so gather not in clusters but in a fine matrix of chains that is much better at retaining liquid in its small interstices.

To pasteurize raw milk McGee explains that it could be heated to 145 F for 30 to 35 minutes or 162 degrees for 15 seconds. So heating the raw milk to 195 degrees for 10 minutes both pasteurizes the milk and improves the consistency of the resulting yogurt.

Ricki suggests you cool the milk to 110 degrees and then transfer it to the Yogotherm to begin the fermentation process. Super Baby Food has you add the yogurt once the milk's temperature dips below 112 degrees, but as you're not incubating the milk, it focuses on keeping the milk above 90 degrees. According to McGee, the maximum temperature the bacteria will tolerate is 104 to 113 degrees F. At these higher temperatures he notes that the milk proteins gel quite quickly, as in under 3 hours. Super Baby Food suggests that the warmer the fermentation temperature, the tarter the yogurt. McGee explains that at 86 degrees F the milk proteins can take up to 18 hours to gel, which

produces a finer, more delicate, more intricately branched network whose individual strands are weaker but whose small pores are better at retaining whey.

Super Baby food suggests that the cooler the fermentation temperature, the sweeter the yogurt. I let the milk cool to 103 degrees - one degree below the high temperature range McGee specified - before transferring it to the Yogotherm. As this was my first time out with the Yogotherm, I wasn't sure how well the milk would retain its temperature, so I didn't want to let the milk get too much cooler for fear it would drop below 86 degrees and the bacteria would become inactive.

After 9 hours, the Yogotherm maintained the fermenting milk at above 90 F. While the milk had thickened slightly, it was nowhere near as close to being done as when I used the Oikos starter. I thought I might have put in the Y4 while the milk was still too hot and ruined my batch of yogurt. But then I talked to my friend Bridget and she said she too had to wait a much longer time for her yogurt to thicken with Ricki's cultures than with yogurt starter.

After 18 hours the Yogotherm maintained the yogurt at above 82 F, so the cultures were no longer active, but it was still 17 degrees warmer than the ambient temperature in the room. More importantly, after 18 hours the yogurt had set beautifully. It was smooth, sweet, and retained the whey very well. The McGee-ification of the recipe was definitely worth the extra effort. I prefer the bacteria available in Oikos as well as the shorter incubation period compared to Ricki's Y4 culture. Once I run out of her Y4 cultures, I'll go back to using Oikos as my starter. Either way, I'm totally hooked on homemade yogurt. And our wee bairn goes through two quarts in about a week anyway, so the quantity is just right.

Yogurt adapted from Ricki Carroll's Gourmet Home Dairy Kit and Harold McGee's On Food and Cooking: The Science and Lore of the Kitchen
Ingredients:

• 2 qt. raw milk
  
• 1 packet Yogurt Direct Set Culture

Implements:

• sieve
  
• 2 qt. pot
  
• 2 qt. glass jar
  
• Dairy Thermometer
  
• Spoon
  
• Plastic wrap
  
• Rubber band
  
• Yogotherm yogurt incubator

Procedure:

• Strain milk through sieve into a 2 qt. pot and affix the thermometer in a readable position.
  
• Put the pot on medium heat and stir occasionally until it reaches 195 degrees. Maintain 195 degrees for 10 minutes by moving the pot on and off the burner while stirring constantly.
  
• After milk has been at 195 degrees for 10 minutes, pour it into a 2 qt. jar and put thermometer in the milk. Cover the top with plastic wrap secured with a rubber band. Put the jar in the fridge.
  
• When the milk's temperature gets down to 103 F, pour milk into the Yogotherm yogurt incubator.
  
• Add the packet of Yogurt Direct Set Culture and stir thoroughly.
  
• After 6 hours, start checking hourly for doneness by touching the top with your clean finger. It should have a thick pudding-like consistency.
  
• When it is at the correct consistency, put the Yogotherm insert in the fridge.

Edited 1/30/2011 to add:
Cultures for Health sells a number of interesting yogurt starters including their Vili Yogurt Starter, which contains Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis biovar. diacetylactis, and Leuconostoc mesenteroides subsp. cremoris.

Edited 2/2/2011 to add:
My friend Bridget just recommended The Cheesemaker as a source for various cultures. She gets her brie cultures and whatnot from The Cheesemaker. He does have some yogurt cultures for sale.

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