When I wrote about making a sparkling ginger mead using Safale S-04 (Fermentis) ale yeast, Carl Swan quite rightly pointed out that I’d said it was a bottom-fermenter, when traditionally ale yeasts are all top fermenters. I had to look into this matter.
My only road back to exactly where I’d seen that information is on a computer I can’t access for a bit, and that’s assuming I could find my way through browser history to the right source (I look at a lot of websites when I’m researching something). Somehow I was under the impression that Safale themselves had said it was bottom-fermenting. In the process of checking, I’ve about memorized everything Fermentis says about S-04 – how it’s known for its quick ferment and compact lees, its preferred temperature range, how it’s recommended for a large range of ale beers. Nothing about where it prefers to ferment. Hm.
What this is about: Yeasts tend to like to either float to the top of your brew and ferment, or sink to the bottom and ferment (as cells die off, they tend to sink anyway). Generally the more flocculent the yeast (the more it clumps), the more likely it is to rise to the surface during fermentation. As a rule, ale yeasts are top-fermenters and lager yeasts are bottom-fermenters. Ale yeasts generally ferment best within a warmer temperature range than lagers. I did see one thread that posited that top and bottom fermentation aren’t so much a quality of the yeast as they are a result of the yeast’s preferred fermentation temps. Yeasts that like cooler temps tend to ferment more slowly, and have more time to settle to the bottom.
Cropping, or collecting yeast from an actively fermenting batch of beer, is often best done from the top during active fermentation no matter what kind of yeast you have. That’s when yeast is at its most vital.
Where I looked: White and Zainasheff’s Yeast. It’s very granular and not brand-specific. It does discuss top-cropping and bottom-cropping yeast (harvesting it). Second check: John Palmer’s How to Brew comments that some modern yeast strains confound the old rule (about ales being top-fermenters and lagers being bottom-fermenters), but he doesn’t cite which ones. His text on Safale S-04 is a copy of what I saw in many places, and it doesn’t mention top or bottom fermentation. Roger Barth’s The Chemistry of Beer. No joy there; this is chemistry (with very helpful illustrations). And on and on…back to thar Interwebz.
No luck retracing my steps without browser history. Then, finally, good ol’ Homebrewtalk.com came to my rescue (you’ll need a login). According to a thread there, the Fuller strain of S-o4 is a bottom fermenter. The kind I bought is Whitbread strain. Brewers Connection (Arizona homebrew store) website says it’s a bottom fermenter, too. That’s only one source, so I don’t know for sure they didn’t get the two confused…but of course, it’s not going to make a huge difference in how I treat the fermenting mead near as much as keeping it within the preferred temperature range will.