Yogurt making problem

[Guest guest]

We're having a strange problem with our yogurt making lately. The past two or

three batches

have not soured or thickened like they normally do.

We've followed exactly the same procedure we always follow, which is to heat raw

milk to 180

degrees, allow to cool to 110, add 1 TBS. of starter (we normally use a

locally-produced

organic, artisanal yogurt, but we have tried two different brands to rule out

the possibility

that there weren't enough cultures in our normal brand). Then we pour the

mixture into a

mason jar, wrap in a towel, and put into an insulated container and let sit for

24 hours.

The first several times we did this it worked very well. The last three times,

however, it has

not become sour or thick. Nothing else has really changed - if anything, it's

warmer in the

kitchen and I would expect fermentation to go faster.

Anyone experienced something like this before? Any ideas what might be causing

the

problem?

Thanks,

Chris