# Temperature range in a body of liquid

1. Sep 22, 2009

### Greg J

Hi,

I am an avid home brewer and I am looking to refine my methods in the fermenting stage. For about 7 years now I have had a cupboard where the temperature of the air inside the cupboard is controlled by a thermostat. The probe is located near the bottom of the vat. There is about 650mm of space below the vat, where the light providing the heating is located and there is about 400mm of space above the vat. The entire space is 1650mm high, 550mm deep and 480mm wide. The enclosure is reasonable well insulated. The body of liquid is approx 48 litres with a specific gravity of 1.032 (start) - 1.010 (finish) over the 7 to 10 day period. The liquid starts at the same temperature as the thermostat, lets say 25 degrees celsius. Every now and again I poke a thermometer down through the airlock to verify the temp and it is typically the 25 degrees celsius. This test is only the liquid at the very top of the vat, I have never tested it further down.

So my questions are:
- is it reasonable to assume that if the air temp in the cupboard is maintained that the temp of the liquid in the whole vat is maintained?
- as the liquid must remain stationary for the entire process, is it likely that parts of the vat may be warmer than other parts, and if that is the case, is it possible that the liquid will slowly move with warmer parts moving to the top and colder parts moving to the bottom?
- and as the heat is applied to the bottom (globe is approx 200mm from the bottom of the vat) would this assist in ensuring the brews temp is consistently maintained?

I am about to introduce a computer controlled environment to the cupboard where I can monitor the air temp in the cupboard as small intervals (ie every 5 seconds). This will tell me of the range of fluctuations to the air temp in the cupboard, what temp the light comes on, what temp the light goes off etc. I was also considering attaching a thermometer probe to the side of the vat and shielding it from the air temp to obtain the temp of the liquid in the vat. In doing that I was wondering if I would be getting an accurate reading by just testing the temp at a point half way up the side of the vat or do I really need to be suspending a probe in the vat itself.

Any advice would be greatly appreciated.

Greg J