Yogurt: an experiment in oven control

Several months ago Phil and I were walking home from downtown and decided to pop into the bookstore at the ÉTS to see what there was to see. After poking around the computer section (Phil) and the stationary section (me), we headed over to what looked like the fun things section and a make-your-own yogurt kit caught my eye. The combination of the little pots and the cute recipe book overcame me and we brought it home.

The box of pots for the yogurt sat on our shelf and the book sat on my bedside table where I would pick it up and leaf through from time to time, my stomach rumbling in happy anticipation of nutella yogurt or honeyed yogurt.

I finally decided to go for it one day. I bought my full fat organic milk. I bought my freeze-dried yogurt culture. I washed the pots and some extra jars and then sat down to read through the instructions once more.

Mes petits pots de yaourt gives instructions for four methods: in a yogurt maker, in the oven, in a pressure cooker, and in a thermos (for emergencies [who has yogurt emergencies??]). Not having a yogurt maker or a pressure cooker, and considering the fact that I was not in mortal peril for lack of yogurt I decided to use the oven. Here's what the book has to say about that:

You can make your yogurt in the oven if you have an oven whose temperature you can control very precisely.

Carefully mix 1 litre of gently warmed milk with 1 yogurt culture. Divide into pots.

Put the yogurts into a 40 degree (C) oven. After two hours turn off the oven but no matter what don't open the door. Leave the yogurts in the oven without moving them for at least 6 hours, then refrigerate them. Serve cold.

Okay, fantastic, no big deal.

But then I looked in The Joy of Cooking, which had quite a lot to say on the matter of making yogurt, but it starts with this:

If you have ever eaten good, naturally flavored yogurt, you will try, as we have, to make it. We hope these directions will spare you some of our exasperating failures.

Exasperating failures doesn't sound too promising. The method that Joy suggests is to build a "snug nest" contraption that retains the heat of the warmed milk. Maybe some day I'll buy the required inch-think foam rubber to do one up, but this time around I decided to stick with the oven method. My oven doesn't have a precise temperature gauge that goes low enough, however. I decided I would continue on... The metric instructions call for 40 C, the English for 106-109 F. That oven setting looks pretty good, right? In a flash of inspiration I thought of a fantastically clever way to monitor the internal temperature of the oven: I stuck my insta-read thermometer into the oven vent and thereby could see the temperature of the hot air as it left the oven.

I'm so smart! If the temperature at this point was juuust a little below what it was supposed to be, then in the oven it would be spot on. So I waited and watched my little jars of inoculated milk through the oven door.

After the prescribed two hours I turned off the oven and waited and waited and waited. When I opened it oven the yogurt looked pretty good. Some of the water had clearly evaporated, at least.

Disappointment struck, however, when I tilted the jar.
Exasperating texture failure - it was still thin thin thin! Why hadn't it worked?
I roasted my bacteria!

I haven't repeated the experiment but maybe next time I'll try to make the cozy nest and stick it in an off oven.

For now I'm working on getting the apartment all tidied up. Little brother is coming for a visit and at the end of August I'm moving up to a new job that will require me to have a good home office space. The professional organizer comes Wednesday to help me get sorted...