As a continuation to my [previous question about a very slow fermentation](https://homebrew.stackexchange.com/questions/80/sloe-wine-going-very-slowly) of sloe wine, I think my demijohn is just too cold where it is. I haven't taken readings - I'm still fuzzy on how - but judging by its activity I'm sure there's plenty of sugar left and not too much alcohol.

Can anybody suggest a safe way of warming it up, without it getting hot enough to harm the yeast? It's too big to fit in the microwave. :)

Once it's warmed up, I assume it will keep its heat for a while? I know after boiling the fruit up, it took until morning before it was even cool enough to add the yeast.