I have read that the temp during fermentation can be as much as 8 deg F hotter than the ambient room temp. this I did not believe although I know that some brewers brew with their FV placed in a bath of colder H2O, However I decided to check this out,my results were that the temp of the ferment was 4 degrees F LOWER than the room ambient !! ?? I am using SafAle T58, this is day 5, brew was 1043 at start.Can anyone shed any light on this please?
Make sure you are taking the ambient room temp at ground level, and that you are taking a temp reading for the liquid at center mass. Surface temp of the carboy could be skewed by condensation on the side of the carboy. If your carboy is touching the ground you will lose some heat to the cold floor as well. On another note if the fermentation is on day 5 it make be complete. A bit more specific information would be useful to complete the assessment of the situation. For this yeast strain you have a safe temp range from 59 - 68 F, as long as you are fermenting in this range the yeast should produce normal esters for you. I wouldn't worry much about 4 F less if you are still within the safe range. Cheers