My process has been honed over the years, as I've improved my recipe design, mashing, boiling, hop additions and all the processes in between and after (bottling and kegging, serving temp, condition). The intermediate step, fermentation, is all down to the yeast. Mishandled yeast can, at best, behave a little odd, throw out some unusual flavours, or take a while to start or stop. Sometimes a poorly treated yeast will give you some bad flavours and aromas. I've got to the point now where that kind of thing is no longer tolerable, and it's apparently bad form to blame the yeast. Acetaldehyde (green apples), Diacetyl (butterscotch), solvents (pear drop esters at best, nail polish remover at worst) phenols (smokiness or pepperiness) and some rubbery aromas if allowed to die and disintegrate in the wort.
So, in the same way as I developed my other brewing skills, I'm now paying some close attention to my yeast. I do have a microscope, but haven't been able to use it properly yet, as I can't get hold of Haemocytometer plates. Nevertheless:
1: Pitching rates- at it's simplest, for a standard strength ale (up to SG. 1060) a single sachet of dried brewers yeast will work fine. For a lager, buy two. They're not expensive. Rehydration can take place before, or by addition to the cooled wort. Rehydration advice found here: http://www.fermentis.com/wp-content/uploads/2012/02/SFA_S04.pdf
For wet yeast (or liquid yeast) I believe one vial treated well will work for a standard strength ale, and again cough up for two if you're brewing a lager, but preparing a starter is the best treatment here.
Repitching yeast from a previous batch (slurry) can help reduce the cost of buying two or more sachets or a vial. Depending on how fussy the yeast, or how obvious it will be in the final beer, I'll either pitch straight onto the yeast cake in the fermenter, or scoop some out (in a sanitary manner) for use later.You wouldn't pitch a pale beer straight onto a stout yeast cake, for example.
2: Temperature- best not to pitch while too hot, or to have a temperature jump from yeast temperature to wort, or large fluctuations in temperature during fermentation (with the exception of a specific fermentation profile, like crash cooling, Diacetyl rests or increasing temperature for Belgian style beers or for attenuation). Also, keep the beer at a suitable temperature for the beer. Warmer temperatures tend to create more esters, while cooler fermentations, though slower, produce a cleaner beer.
Most beers ales are fine fermented between 16 and 20 degrees C, but do check. Also, picking yeast best suited to your actual ambient temperatures can work. WLP029 Kolsch yeast is a warm lager yeast, fermenting a clean beer at ale temperatures, and I've got Nottingham to work quite well at quite low temperatures.
3: Style- pick a yeast suited to the beer style brewed. I'm spending a few extra euros for wet yeasts, of which there is a much wider variety. Spending more money on Saaz and brewing water adjustments, pilsner malts and making space in the fridge is a waste without the perfect yeast for the job*. That's not to say that good beers can't be brewed with other yeasts, of course. Stout brewed with Belgian yeast, IPA with Brett, My next step is to make a stir plate (read here for the reason I chose not to http://www.jimsbeerkit.co.uk/forum/viewtopic.php?f=12&t=70926), and aquire some Erlenmyer flasks in order to make some starters a few days in advance. I've bought a pressure cooker to sterilise wort in jars, and then I'll feel I've really got the hang of brewing.
*And for this prize of which I mention in the title, the yeast is Vermont IPA yeast (Conan). This is being fermented warm in my specially designed fermentation chamber (which has cost about a tenner to make from begged stolen and borrowed gizmos). The beer is an America IPA for the Galway brewer's competition. It didn't make it in, after all, but I enjoyed drinking it, I suppose.
