Yesterday I decided to try to make my own yogurt, just for kicks. I heated a quart of 2% milk to not-quite-simmering, stirred in a touch of half-and-half for richness, sat it by the window to cool, watched the Daily Show online, realized it was now too cool and put it back on the heat until it was just over 100 degrees, mixed in ~4 tbsp plain live-culture yogurt, and let it sit in a warm oven for about 10 hours. (My oven's lowest temp is 170, so I turned it on to that but turned it off before it had reached 170. I then turned it on again once or twice during the 10 hours just for a minute or so to keep things warm.) The resulting yogurt has an incredible delicate flavor, but it's thinner than I'd like, as though it got 80% of the way from plain milk to the consistency of Dannon and then gave up. Next time, should I let it sit longer? (Most recipes I saw said either 4-6 hours or 8-12, so 10 seems like it should be enough?) Add more starter? Keep it somewhere warmer? Did the cooling and reheating screw something up? Also, to make flavored yogurt - can things like sugar and vanilla be added to the milk at the beginning, or do I wait and stir them into the yogurt later?
I'm in the midst of making yogurt cheese out of half of it; after sitting overnight it's almost to the consitancy of Fage yogurt. In the future, can I stir in add-ins for that (I'm thinking garlic & basil) when I start draining it, or will that mess up some chemical reaction?