Does the ideal fermentation temperature range given on a package of yeast mean the ambient temperature or the internal temperature of the fermentation?
Internal (wort) temperature. (Good question)
Cheers!
There is I think a bit of a consensus among a number of frequenters on this forum that Mfr. temperature ranges should be taken as a suggestion, not necessarily as religion. A goodly number of yeasts will perform well outside the suggested temp. ranges listed by the manufacturer.
I’d add that there won’t be a significant difference in temperature between a temperature probe in the middle of a fermenter and one that’s well-adhered or well-insulated on the outside, at homebrew scale.
I am not sure what you mean.
Fermentation is exothermic, which means it will create its own heat. Having the ability to cool the wort once it starts fermenting, and maintaining the wort temperature within a tolerance range is considered a best practice.
While the manufacturer’s temperature ranges may not be the best guideline, all yeasts produce different results at different temperature ranges. Some strains are more forgiving than others, but being able to control your fermentation temperature will let you control your fermentation character better and produce consistent results. For example, I’m brewing a hefeweizen with WLP351 right now. White Labs lists the optimum temperature as 66-70F. I’ve found that I like the results much better when I ferment it at 62F. There is a subtle vanilla/cinnamon character that is enhanced by a cooler ferment and gets lost when I’ve brewed it at 68F.
tl;dr - The manufacturer’s listed temps aren’t always the best guide, but fermentation temperature does matter. And it is referring to wort temperature, not ambient.