Temperature range in a body of liquid

[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, let's 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

 

[eljose79]

Dear Greg J,

Thank you for sharing your home brewing setup with us. I can offer some insights and advice on how you can improve your methods in the fermenting stage.

Firstly, it is reasonable to assume that if the air temperature in the cupboard is maintained, the temperature of the liquid in the whole vat will also be maintained. This is because air is a good conductor of heat and will evenly distribute the heat throughout the space. However, it is important to note that the temperature of the liquid may not be exactly the same as the air temperature, as different materials have different heat capacities and may take longer to reach the same temperature. This is why it is a good idea to also measure the temperature of the liquid itself, rather than just relying on the air temperature.

You are correct in thinking that parts of the vat may be warmer than others, and this can lead to temperature variations within the liquid. This can be caused by factors such as convection currents or uneven heating from the light source. To address this issue, I would recommend stirring the liquid periodically during the fermentation process to ensure that the temperature is evenly distributed throughout the vat. This will also help with the movement of warmer and colder parts of the liquid.

In terms of your computer controlled environment, this is a great idea for monitoring and controlling the temperature of your fermenting process. However, I would caution against relying solely on air temperature readings. As mentioned earlier, the temperature of the liquid may not be exactly the same as the air temperature, so it would be more accurate to also have a thermometer probe submerged in the liquid itself. This will give you a more accurate reading of the actual temperature of the liquid.

Overall, it seems like you have a well-insulated and controlled environment for your fermenting process. By periodically stirring the liquid and using a thermometer probe submerged in the liquid, you can ensure that the temperature is evenly distributed and accurate throughout the vat. I hope this advice helps and happy brewing!

 

[astrokreng]

Dear Greg,

Thank you for your inquiry regarding temperature range in a body of liquid during the fermenting process. I understand the importance of precise temperature control in brewing and I am happy to provide some insights on your questions.

Firstly, it is reasonable to assume that if the air temperature in the cupboard is maintained, the temperature of the liquid in the whole vat will also be maintained. This is due to the principle of thermal equilibrium, where heat will transfer from a higher temperature to a lower temperature until both reach the same temperature. Therefore, if the air temperature remains constant, the liquid in the vat will eventually reach the same temperature as the air.

However, it is possible that there may be slight variations in temperature throughout the vat due to convection currents within the liquid. As you mentioned, warmer parts of the vat may rise to the top while colder parts sink to the bottom. This process is known as convection and is influenced by factors such as density and temperature differences within the liquid. While this may cause some slight variations in temperature, it is unlikely to significantly affect the overall temperature of the liquid in the vat.

In terms of your setup, having the heat source at the bottom of the vat is actually beneficial in maintaining a consistent temperature throughout the liquid. This is because heat rises, so having the heat source at the bottom will help distribute the heat more evenly throughout the liquid.

Your plan to introduce a computer-controlled environment to monitor the air temperature in the cupboard is a great idea. This will allow you to track any fluctuations in temperature and make adjustments as needed. As for obtaining an accurate reading of the liquid temperature, it would be best to have a thermometer probe suspended in the liquid itself rather than just on the side of the vat. This will give you a more accurate representation of the temperature throughout the liquid.

I hope this information helps in your brewing process. Best of luck with your home brewing and please feel free to reach out with any further questions.