Success with making delicious tangy dahi (दही, yogurt) at home!

I miss having home-made dahi, that staple of Indian meals. I've been making do with Pavel's Russian plain yogurt which comes very close though the consistency is thicker than our dahi, and Verka Dahi, which again is thicker and sweeter than the home-made variety.

I made one unsuccessful attempt to make it at home using the culture from Verka. There were three possible reasons why it went wrong:

• I microwaved the milk too much - it had boiled over.
• I didn't cool it enough - it tried the finger in hot milk for 10 seconds test and at the 8th second, my finger was burning hot but I mixed in the culture anyway. I probably ended up killing the yogurt bacteria.
• I didn't maintain the temperature of the container between 100 and 120°F for 8 hours.

I think the 3^rd reason is likely the largest contributor to the failure. The problem is I didn't quite know how to maintain the container at the said temperature; what to use to do this. I considered a few possibilities. A crockpot that can stay warm for hours on end, a toaster oven that I'd set up to stay on at the lowest temperature (which was 150°F unfortunately), the big oven that I'd preheat to 350° and then keep the light on. I wanted something convenient so that I could repeat this forever with minimal trouble. There are directions on the web on keeping ovens within the said temperature but they require one to constantly adjust the settings so the oven doesn't get too cool or too hot, and I was looking for something that did its job overnight. Finally, I settled on a ceramic bowl inside one of those soft thermal lunch bags. I moved the contraption inside my heated room so that the thermal bag didn't have to work too hard. Next morning, I went and looked and it looked like the culture had died too soon because there was a layer of curdled milk on top but the rest of the milk was untouched though slightly sour.

Well, yesterday, I decided to try again. This time around, instead of 300 ml (~10 oz) of good fresh milk, I chose a small glass of milk (about 150 ml, 5 oz), wholefat and non-homogenized, since if it didn't set again, I didn't want to waste so much milk. And besides, I figured that it'd be easier and more likely for bacteria to work on a smaller volume of milk in potentially inhospitable conditions. Microwaved it for about 1 minute 40 seconds at which point the milk had steamed but not boiled over. Then, I made sure to cool the milk enough. I didn't mix it with culture until I could keep my finger in the milk very comfortably for 10 seconds. Once it had cooled to this point, I poured a bit of milk into a separate bowl and mixed it with about 2 heaped teaspoons of yogurt (containing live cultures). And then poured this starter into the glass and stirred lightly so that the culture was well-spread-out through the milk. Remembering a tip from my mom, I lightly rubbed some of the yogurt on the sides of the glass. I set up a heating pad at medium, put the glass (with cover) on it, then rolled the pad over so it covered the glass, and also bundled the glass with towels to preserve the heat. I didn't touch the contraption until morning. The key, I hear, is to not disturb setting yogurt and let the bacteria work their wonder in peace or you will end up with runny yogurt. When I went to check in the morning, what I found was a delicious well-set glass of dahi. Spooning out a morsel, I was amazed to find that it had a nice, subtle tangy taste, the kind we have with home-made dahi in India. I'm overjoyed with this success, and especially because it seems like this could be repeated - there was nothing that was awkward to set up or left to chance.

I've had a nice glassful of delicious yogurt today, with just the taste I like. I've taken out a couple of spoonfuls to use as the starter for tomorrow's glassful. Hope this experience helps others who're experimenting with home-made dahi too.