First, a preface as this is my first proper post. From reading these boards it seems this place is very up for challenging received wisdom and superstition when it comes to brewing. Hence I have posted this here rather than other forums as I am aware the thread title may come across as slightly inflammatory but I am trying to understand the parameters and real goal behind temperature control of fermentation as it relates to fermentation activity.

Most information I have seen is of the "you must control fermentation temperature or you will not get good beer". Clearly this is not true - you may still get good beer. You are unlikely to consistently produce good beer and this is fair enough and likely true.

My case in point - I am currently fermenting an pale English style ale with S-04 and it is the dead of winter here. This is my Sixth brew total (fifth AG) and first time making even the most cursort attempt at temperature control, wrapping the fermenter in a sleeping bag. The brew started out around 15C and peaked at just over 17C two or three days into fermentation. We had a cold snap Monday into Tuesday (outside ambient temps dropped to -5C) so when I got home from work on Tuesday evening the temperature of the beer had dropped to 14C. However, I do understand that it is better to be on the low end of a yeasts recommended temperature range and also that S-04 is quite a forgiving yeast so I am in no way panicking.

So the meat of the issue - is the point of temperature control to maintain as close to a precise, constant temperature as possible or to keep within the yeasts recommended operating temperatures, whether manufacturer advertised or established through experience? I am unlikely to be getting any more sophisticated in the near term when it comes to temperature control so this will probably affect the degree to which I am fussing over the fermentation (eg. last night I had it beside a radiator to bring temp back up to 15.5C before tucking it up again).

Well, I had intended to brew a Hefeweizen (first attempt at this a couple of brews ago did not go well at all) next but having thought about this I will probably leave that until the summer when the ambient temperatures will be more suited. I'm in Northern Ireland and we would rarely see temps above 22-23C but ambient temperatures in the summer should be good (as far as I understand) for a Hefe in the upper "Banana" type range.

Brewbelt and temperature controller might be doable.