In this article discussing beer, it is said that in medieval times yeast (possibly only brewer's yeast) was called godisgoode. Is that the case? (Searching on Google sheds very little light on the matter.)
It's not just that article. Here's a book which has it:
Bread and ale, both packed with calories and nutrients, lay at the heart of all diets, and ale barm was so vital that it was sometimes known as godisgoode 'bicause it cometh of the grete grace of God'.
Searching for the last quote, I found a site with this information:
In her splendid book on English bread and yeast cookery, published by Allen Lane, Elizabeth David has this to say: In Chaucer’s England one of the names for yeast or barm was goddisgoode ‘bicause it cometh of the grete grace of God’.
At any rate, it appears that it's not just one person's tale.
Berme [yeast], otherwise clepid [called] goddes good [god's good], withoute tyme of mynde hath frely be goven .to ye value only of a ferthyng .bicause it cometh of ye grete grace of God.
This appears to be as definitive as it gets.
Update: Andy Connelly, the author of that article, just got back to me:
...I would love to say that I had a water tight source for the origin of "godisgoode" but I don't. The term is all over the blogs and books on beer so I accepted it as fact. However, it could be a convenient, rather than actual, fact (like Marie Antoinette's "let them eat cake" line). I have set a couple of friends on looking into the relevant places to search out a source if we find one I will let you know.
We'll see if they get any further than I did.
Andy Connelly contacted me again to let me know that he and his team did not, in fact, get any further than the online ME dictionary I had already found, so the issue has finally moved beyond my range:
Best I can find:
Have a look at 4c
goddes god - God's gift, yeast
Spelling is a little different but I can see an modernised version stretching to Godisgoode (with an extra e for effect). However, I am no middle English scholar!