Yogurt

Homemade yogurt!

Concept

The Problem

The wife has a taste for Greek-style yogurt, but it's fairly expensive. I had made yogurt in the past, but got out of the habit because it's not significantly cheaper than the plain yogurt I bought anyway, and the novelty of babysitting the incubation for most of a day wore off.

How It's Done

The theory behind making yogurt is very simple. Milk is heated to a certain point (the usual recommendation is 180-185°F) to destroy any "bad" bacteria, then is allowed to cool to around 110°F. Seed cultures ("good" bacteria) are then added, either from freeze-dried yogurt starters or from a few tablespoons of store-bought plain yogurt (ensuring that the packaging says it contains live and active cultures). That temperature is maintained for 6+ hours until the yogurt sets and acquires the desired taste; longer incubation produces more tartness. Heating the yogurt cultures beyond about 120°F will kill them, and letting the temperature drop below around 100°F will deactivate them.

Ideas

We set out to perform our first test with equipment we have on hand, rather than buying a purpose-built yogurt maker. For the heating stage, we used a makeshift double-boiler out of a large metal bowl and a 6-ish quart stock pot.

For the incubation period, there are lots of options. Some we considered are:

• Cooler. This is what I used my first time around. I poured the heated yogurt into individual-sized jars, placed the jars in a cooler, filled the cooler up close to the top of the jars with hot tap water (which at my previous abode was 120°F), and covered it. I'd check the temperature in the cooler every couple of hours and replace water as necessary. Took about 8 hours to get the appropriate tartness.
• Heating pad. Works well for some people, and the wife wanted to try this method until she realized she didn't actually have one.
• Slow cooker. Heats too hot if left to its own devices, but if babysat a bit, would be pretty simple to keep it in range.
• Warm oven. Some folks get an appropriate temp in their oven with just the pilot light, but we have electric. Others recommend turning the oven light on, but I don't think that'll do it, at least in winter.

Development

First Batch

Seed Culture

The wife is fond of Fage Greek-style yogurt, so we decided to use that for our cultures.

Heating

As mentioned, we have a cheap metal bowl (holds a bit less than a gallon) that fits nicely inside our biggest pot with a little room at the bottom.

Setting it up as a double-boiler, it only took 5-10 minutes to get our half gallon of 2% milk up to 180°F.

Incubation

For the incubation phase, we poured the milk into the inner bowl of our small slow cooker. We let it come down to 120°F and then placed it in the same stock pot used for the heating phase (whose water was also down to about 120°F). We used three towels to insulate the setup: one folded underneath, one wrapped around the stock pot, and one folded and placed over the top. We left our thermometer probe inside the yogurt container to track the temperature.

We were amazed at how well this setup incubated the yogurt. After hours it only seemed to lose a couple of degrees. I got suspicious, but it still felt warm inside the blankets, so let it go.

Final Product

After 8 hours, we unveiled the final product... which was not at all thickened. While the water felt warm, it didn't feel 110°F warm (the thermometer still registered 108°F). I grabbed my candy thermometer, and lo and behold, it only registered around 80°F. Oops.

I boiled some water and poured it into the water bath until the candy thermometer registered around 115°F and let it sit for a few more hours. The temperature dropped much more rapidly this time, although in fairness it did have to reheat the pot of 80°F yogurt back up, so I'm still not actually sure how effective the towel insulation is. After 2-3 more hours, though, finally the yogurt was a reasonable consistency.

Straining

To make the yogurt "Greek-style", we lined a colander with cheesecloth and poured the finished yogurt in to strain out the whey. We left it overnight, and by morning it had a similar consistency to the Fage (the wife says it's actually a bit thicker).

Taste Test

The homemade yogurt has a similar consistency and mouthfeel to the Fage. Though the homemade didn't quite reach the same level of tartness as the commercial, it did have a similar flavor profile. Getting better temperature control would probably improve our control over the tartness.

Lessons Learned

Our thermometer, though it's happy to display temperatures much lower, apparently has awful accuracy in the vicinity of 110°F. Testing it against boiling water, it seems to be ok in the actual cooking range.

Leaving the yogurt straining overnight might be a bit too long, as the end product ends up even thicker than the commercial Greek-style yogurts.

The initial trial was a qualified success. Though the improvised setup worked reasonably well (other than the thermometer), since we both enjoy yogurt and would be making it fairly often, we took the plunge and just purchased a Yogourmet 2 quart yogurt maker to handle the incubation for us.