Homemade Yogurt

Microorganisms are a huge part of my life.  I am a clinical laboratory technologist and love the study of microbes and parasites.  Most people say yuck when I get excited!  This has lead to a fascination with cultured foods.  So much of what we eat is dependent on the action of microrganisms. 

A few years ago I experimented with homemade kefir.  Kefir is similar to yogurt in that it is a fermented milk product.  It is much runnier and contains different bacteria.  The freeze-dried cultures I used for making kefir were not ideal but I did not have a good source for kefir grains and was not super impressed by the taste either.  Kefir is great for drinking and making smoothies but I love yogurt with granola and fresh fruit for breakfast or a snack.  Kefir just does not lend itself to this type of dish.  Plus I was using a stove-top which was somewhat labor intensive.  I decided it was not worth the effort to keep pursuing this prep method.

More recently, I began reading again about homemade kefirs and yogurts.  I found several sources for making crockpot yogurt or other incubation methods.
 
http://www.keeperofthehome.org/2011/04/making-homemade-yogurt-2.html
http://www.thefamilyhomestead.com/yogurt.htm
http://bornambitous-bornimaginative.blogspot.com/2011/03/yogurt.html

This sounded like a great idea!  So I tried it.....with not so great results.  I sterilized the milk in the crockpot and let it cool.  I used Stonyfield yogurt and kefir cultures as starters.  I added powdered milk and even pudding mix to one batch.  Each time I got slightly thickened milk.  Yuck.....well it did make some great strawberry smoothies and banana/Nutella smoothies but I still wanted thick yogurt. 

Then I said to myself, you are a scientist!  You can figure this out!  So I read more recipes and thought about the process and concepts behind it.  As long as the crockpot was turned off, that milk was going to cool down.  Over several hours it will reach room temp.  Bacteria does not grow well at room temp, well Yersinia does but we are not detecting stool pathogens here (at least I hope not!).  My hypothesis was that the temperature of the crockpot after cooling was not sufficient for adequate growth of the cultures.  So I filled my crockpot with water.  I heated it up.  I unplugged it and monitored the decrease in temperature.  Sure enough that crockpot was not staying warm very long!  I will save you all of the data points but I knew what I had to do!

Bacteria grow best at body temperature.  I wanted to maintain a temp of 95-105 degrees.  My oven cannot be set that low so that option was crossed off.  My crockpot has a low and high setting.  I needed a warm setting or a precise thermostat but I wasn't going to go out and buy a new crockpot.  So today I did another experiment and had success!

I added about half a gallon of milk to my crockpot and heated on high for about 2.5-3 hours.  After the heating process, I turned the crockpot off and let the milk cool to about 110 degrees.  I added powdered milk and about a half cup of Stonyfield.  I checked the temperature of the mixture every so often.  I was not really precise with the time intervals, just checked when I had a break in the other projects I was working on this afternoon.  When the temperature was dropping below 100 degrees, I turned the crockpot on low.  I let it heat for about 10-15 minutes and turned it off again.  I did this twice in about 5 hours and by then the yogurt was a great consistency!  Not as thick as some varieties but enough that I could eat it instead of drink it. 

I am so happy that I found a solution.  One more thing that we can do ourselves at home!