Yogurt making

Well, after this post on my home made yogurt, I’m running out of fermentables to write up, I think only bread remains undocumented. Yogurt making is actually one of the primary reasons I started this blog, as it was Jen B.’s interest in it that prompted all this. However, I only make yogurt once a month at most so it has taken a while to be able to take pictures of the process (and on the day I made it one camera was out of power, and the other with my wife, so I had to use an actual film camera with a few pictures left, then get them developed - can you notice difference? The last 3 pictures were taken with a digital camera) . I usually make five tubs of 750 ml in each batch, which lasts us for over a month often.

This longevity is, I believe, the original reason for making yogurt - as a way to preserve dairy products. Only one batch (when I discovered that my electronic thermometer gives funny readings when immersed in water for long periods) had issues - a bit of mold growth on the sides of the last tub when I opened it (but the yogurt itself was OK - at least, nothing happened to me after eating it). The reason for the mold was that because my thermometer was not working properly, I was not holding the yogurt at high enough temperatures, so it did not acidify enough, which in turn made it more susceptible to mold infections - but only marginally so.

So, the theory behind yogurt is to ferment milk using a lactobacillus/thermobacillus culture to acidify it to help preserve it, and (a bit less clear on this part) to make it more easily digestible by adult humans. Initially the milk should be scalded - briefly brought up to at least 95 degrees . From what I understand, this is to modify the milk protein (makes the yogurt thicker and taste better), and probably kills off most competing bacteria. To properly and quickly ferment, the milk must then be held at temperatures between 40 and 50 degrees for several hours.

In practice, this is how I do it:

Here I have assembled the ingredients (milk, and store-bough active culture yogurt) and the scalding pot and thermometer.

Here the thermometer shows 95 degrees - the milk has finished scalding. I use only medium heat to do this as I find that it means less burned-on milk at the bottom of the pot, and it is easier to prevent boil-overs.

After scalding the milk, I cool it down to about 55 degrees (here the thermometer shows 53) in a cold water bath in my sink. This takes about 5 minutes - if I stir both milk and water.

Here I have divvied up the starter culture between the five tubs I will be using (I used Astro's Balkan style yogurt this time - this was the best culture I have used so far, as it made a very thick and proper yogurt). Although this means only 150 ml of yogurt starter per tub, I have not had any trouble starting fermentation.

Here is how I ferment the yogurt. I place all 5 tubs in this picnic cooler, and immerse them in the hottest tap water I can get - usually around 54 or 55 degrees. I then monitor the temperature, and when it falls to 40 degrees (usually takes at least 90 minutes) I empty the water and refill it with hot tap water again. I usually do this 3 times.

Here's a comparison of temperature readings from my electronic thermometer and my brewing thermometer. The electronic one shows 53 degrees, while the brewing thermometer shows only 49 degrees. Not sure why or which one is right, but I trust the brewing thermometer more!

This is what yogurt making looks like for most of the time it takes to do.

The finished product! After about 4.5 hours, the fermentation has acidified the milk, and it has turned into a nice thick yogurt. Notice how rigid it has become - even when tilted to a 45 degree angle. To me, it tastes pretty much the same as yogurt I buy (others describing their own yogurt say it tastes 'creamier'; the only time I found this to be true was the time it did not acidify enough because my thermometer mislead me, and it did not ferment properly). I have also read elsewhere that you should mix in dehydrated milk powder to achieve the thickness of commercial yogurts (or that commercial dairies add artificial thickeners to achieve their thickness). I don't really agree - my yogurt has always been as thick as the stuff I buy, so no need to add any milk powder, and it makes me doubt that artificial thickeners are neccessary even on a commercial scale - lactic acid works fine. What probably is happening is that people making their yogurt at home may not be keeping it warm long enough to produce sufficient acid, or they are not keeping the temperature high enough.