Once upon a time there was a farmer who had a horse with a very long mane. Unfortunately, birds found this spectacular mane irresistible and insisted on building their nests in it. The worried farmer sought advice from a neighbor who suggested sprinkling yeast on the mane so that the birds would rise (and no, that's not the big pun yet).
So the farmer went home and sprinkled yeast on the horse's mane and the birds rose and flew away just as promised and both horse and farmer were much relieved. Thus, the moral of the story is: Yeast is yeast and nest is nest and never the mane shall tweet.

Do I owe you an apology for that one?

Yes.

Groan. Sounds like you've attended lectures at the P*D School of Humor.