Our supply was running low, so I whipped up another batch of yogurt. Last time, we had 2% milk (the grocery store had run out of our usual 1%) and the yogurt thickened nicely in 3 hours. This time, we used 1% and it took four-ish hours to get to the same consistency. Do any yogurt gurus know if this is normal?

I also was pretty haphazard about the addition of the dry milk last time, so since I was more precise this time (and probably added less), this could perhaps have had an impact as well?