I know that fermentation generates heat. I've demonstrated it to myself by measuring the temperature inside and outside an uncontrolled fermentation and seen as much as 8 °F difference. But I have also seen that in my 50 °F cellar, the beer in my carboy never gets above the temperature I have my set on my Johnson controlled FermWrap.
So when I see a recipe say, "Start fermentation at 64 °F and allow to free rise to 69 °F," and I have seen some professional brewers give this advice, what does it mean?
I mean, if the ambient temperature is 64 °F I can imagine one thing happening, but if the ambient temperature is 85 °F, it will be another, and if I control the temperature, well then I'm not exactly letting it free rise, am I?
So, what does it mean?