My fermentation bucket is on top of my washing machine, when it spins it vibrates the brew.
I've been careful to clamp it to the back of the washing machine with a bungee otherwise it might shake off.
Just want to check that this is a good thing, presuming this agitation is good for the yeast?
In the first stage of fermentation it could be some good. Yeast needs oxygen to the growth phase, when building membrane and other things needed to increase the cell count. When this oxygen is over, then the yeast can take its anaerobian way, and produce alcohol and carbon dioxide, which is needed for beer making. But if you shake your wort vigorously some seconds/splash it to your fermentor before you leave it alone, you get a good enough amount of oxygen.
If you never stop agitating it, maybe it could over-oxygenate your brew, or oxygenate after complete atenuation - don't know if it makes sense considering a very leak proof fermentor; after some time the whole atmosfery of the fermentor would be carbon dioxide, considering that tight environment. But any oxygen after the end of fermentation could feed beer spoilers that you don't want. And I don't know what would happen to your alcohol production.
But nonetheless, you want to settle solid things of your wort, including dead/inactive yeast cells. So, even if it was good to yeast growth phase, you would need to leave it alone after that.
So I think it is a bad idea. If it is a matter of space, you could put a shelf above your machine, or build a rack that envolve it like an outside frame but don't touch it. Good luck!
I would also be concerned with the washing machine's effect on your wort temperature. If you use hot water "for your whites", that heat will rise, right into your fermenter. Where I live, (Florida) keeping the wort cool is a real challenge, especially during the first few days of fermenting when the alcholol level is not yet high enough to limit yeast growth; off flavors plague me when I let new yeast breed too fast. Might be different where you live, but its still worth consideration.
I don't know the answer, but vibration and agitation are not the same thing. I don't think the vibration from the washer will do much to keep yeast in suspension. I do think I read once that vibration can stress yeast out. But at what frequency I don't think that is clear.
It probably won't help.
Agitating the wort to add oxygen is often a good idea (particularly with higher-gravity beers), but the washing machine won't give nearly enough agitation for that, and it is in any case only relevant before the fermenter is closed. Once primary fermentation starts, any oxygen in the headspace will be flushed out by outgassing.
As for keeping the yeast in suspension, most yeast are not so flocculent that they'll drop out before fermentation is complete. You might slightly speed up fermentation by vibrating the wort in this way, but I doubt the difference would be measurable.
