Good old Wikipedia does the job of defining
Racking.
The Home Distiller wiki also defines the term, but in brief:
RackingThe process of siphoning the beer or wine off the
lees to allow clarification and aid in stabilization. A
Racking Hose or tubing is used and can be attached to a
Racking Cane to make this task easier.
Wikipedia has more pictures. Neither really explains
why a distiller would bother racking off. Sam_and_liv gets closer to the money with his 'the end product is more pure'.
There seem to be two scenarios in which people 'rack' their ferments.
- During fermentation. Some people 'rack' or decant the fermenting liquid from an open container into an airlocked container if the initial stage of fermentation produces a lot of foam (due to high protein ingredients). Once that foaming has settled they 'rack' the ferment to reduce exposure to airborne bacteria.
- After fermentation is complete. Some people 'rack' or transfer the fermented liquid from the fermentor into another container (usually a clean fermentor) to aid clarification or, as what I do, to eliminate the chance of disturbing settled yeast when moving your wash to your boiler.
Which raises the question:
Is 'racking' a habit that I've kept from my Turbo days? I always thought that yeast cells exploded at the high temps you get in a boiler, producing off tastes. Is that true or BS? Quite a few people who've been around for some time don't worry about racking or clearing washes.
And you'll find a glossary of other terms here.