Wet towel trick - are we just fooling ourselves?

**Grinder12000** · 07-30-2008, 01:11 AM

We all know that putting a wet towel or t-shirt around your carboy and a fan will lower the temp of the fermentation . . . or does it??

The typical measuring instrument is a plastic thermometer on the outside of the carboy.

Of course it will be cooler. The glass is cooler, and the thermometer is right next to the towel.

What is the temp 2 inches away from the glass in the carboy.

This has probably been discussed a LOT but I could not find an answer for a study on the inside temps.

Anyone?

polarbearbrewing · 07-30-2008, 01:29 AM

as long as the outside of the carboy stays cool it will eventually distribute to the inside...just watch how much that beer moves around while its fermenting

MayDayBrewing · 07-30-2008, 01:32 AM

I don't know the scientific term for it, but there is a phenomenon where evaporating water cools its surroundings. For example, you can spray a fine mist of water into the air on a hot day in your yard and, even without the water hitting you, it will cool down the yard. There are some neat "air conditioner" designs that use some type of water evaporation near a fan (usually a towel or something that passes through water).

See "http://www.newton.dep.anl.gov/askasci/gen99/gen99406.HTM" for another explanation.

Philip1993 · 07-30-2008, 01:43 AM

Simple answer: It takes heat to turn water into vapor.

Stevorino · 07-30-2008, 01:52 AM

It does cool down the carboy-- but it's not a suitable means of controller fermentation temperature if you are trying to make the best beer possible.

**Grinder12000** · 07-30-2008, 01:53 AM

I understand all of that but perhaps a 5 degree drop on the outside of a carboy where the temp is taken is less then 1 degree two inches into the carboy?

I know in THEORY it looks good but does a 5 degree drop = 5 degrees in the middle?

The reason I ask is I am fermenting as I type - will a 3 degree drop on the OUTSIDE of a carboy make that big of a deal to the 99% of the rest of the beer.

I know I'm sounding anal but all I have heard or read is theory and I'm seeing holes in it.

Stevorino · 07-30-2008, 01:55 AM

Quote:

Originally Posted by Grinder12000

I understand all of that but perhaps a 5 degree drop on the outside of a carboy where the temp is taken is less then 1 degree two inches into the carboy?

I know in THEORY it looks good but does a 5 degree drop = 5 degrees in the middle?

On the Brewing Network, Jamil talked about an experiment that said that the wort closest to the glass in a fermenter was within 1 degree from the wort in the middle of the fermenter.

For this reason, he justified taping a probe to the outside of the glass fermenter (but protected from fridge fan).

For the record-- this experiment wasn't something he did-- it was a published experiment given credibility by commercial & big-time homebrewers.

BrianP · 07-30-2008, 01:56 AM

It's call evaporative cooling. That's why sweating cools you off.

CGengo · 07-30-2008, 01:57 AM

Quote:

Originally Posted by MayDayBrewing

There are some neat "air conditioner" designs that use some type of water evaporation near a fan (usually a towel or something that passes through water).

That's called a swamp cooler and they work well in drier climates - we use to have one on our house when we lived in CA. If I remember correctly, you have to leave your windows open so that the moisture will exit the building. Anyway, I did this on a couple batches of beer before buying a Johnson control and it worked well in keeping the fermenter cool although I would imagine it works considerably better on glass carboys than plastic fermentation buckets due to glasses better conductivity.

http://en.wikipedia.org/wiki/Evaporative_cooling#Evaporative_cooling

**BierMuncher** · 07-30-2008, 02:34 AM

Quote:

Originally Posted by Grinder12000

...I know I'm sounding anal but all I have heard or read is theory and I'm seeing holes in it.

Good question. Here's my finding on a 10 gallon batch of my SMaSHed Nugget Pale Ale...one glass carboy in a water bath with a t-shirt and fan, one plastic bucket standing dry.

I dropped a probe into the middle of both beer 24 hours in and the carboy was chugging along at 66 degrees. The plastic fermenter was fermenting at 75 degrees.

A 9 degree differential between a simple water bath and a dry fermenter.

Done.