Fermenter temperature control and aeration

[PeteB]

None of my fermenters are jacketed, and in Australia we are heading towards summer. Last summer they ran a bit hotter than I would have liked on a few occasions.

Can anyone forsee any problems if I circulate some of the ferment through my heat exchanger to cool it?

The return pipe could splash into the fermenter giving some aeration as well!

[Rich Morgan]

Pete,

I would use an immersion coil, passing actively fermenting wash through a chiller is not advisable. We use coils with our condenser water, it's enough to keep everything below 35C. Dry ice is a good backup.

Aeration during fermentation is also not advisable either. Yeast typically multiply in aerobic enviroments, and ferment in anaerobic situations. Aeration is only ever done prior to pitching.

Rich.

[Absinthe Pete]

What he said. If you already have a chiller it's not that hard to add a flexible line, such as corrugated stainless steel to create a cooling snake.

http://morewinemaking.com/view_product/6800/103259/Cooling_Snake_-_80_Meters

Also you'll want to use a system that has a temperature probe as well and use the chiller/heater all the time if you plan on making consistent tasting batches all the time. The more you are able to keep the wash the same as every other batch the more likely you are to make consistent tasting batches and temperature is one of the most important.

What kind of wash are you making and are you sour mashing it?

[PeteB]

Thanks Rich, I didn't realise aeration should not be done after pitching.

Adsinthe Pete, I am making a 100% rye and lautering, not doing a sour mash.

[meerkat]

A local commercial plant with 300 m³ fermenters uses external plate heat exchangers with a pump-around for temperature control. As long as the seals do not give any problems with taste or smell there is no problem. This plant reports that fermenter temperature control is their most important factor in achieving good yields, and also very important in achieving good quality. As a general rule higher temperatures result in faster fermentations, but poorer quality and yield. Breweries ferment at around 10 C or even below because they do not have the option of distilling out what they do not want. 32C seems to be a good compromise between quality and productivity, but I know of commercial plants using higher temperatures than that.

I agree with Rich that aeration at this stage should be avoided.

[Edit Nov 2 - Brewing temperature typo fixed from 0 C to 10 C]

[nick jones]

Pete,

I would use an immersion coil, passing actively fermenting wash through a chiller is not advisable. We use coils with our condenser water, it's enough to keep everything below 35C. Dry ice is a good backup.

Agreed. I would imagine that cavitation in your pump due to CO2 off gassing would be a huge pain in the butt.

Aeration during fermentation is also not advisable either. Yeast typically multiply in aerobic enviroments, and ferment in anaerobic situations. Aeration is only ever done prior to pitching.

I agree that the process that Pete describes would not be an advisable way to aerate wash during fermentation, but the careful aeration of actively fermenting HIGH GRAVITY washes can be a very good idea. As Rich says, aerobic means yeast growth, and anaerobic means fermentation, but in the case of washes with a starting gravity in excess of 15-20 brix, a little growth in the middle of fermentation (around the 5-10 brix range) can be greatly beneficial for a clean, healthy ferment. The judicious use of O2 at this point is warranted, in my opinion.

Have fun, Pete!

Nick

[PeteB]

I am in no doubt cavitation would be a big problem with a centrifugal or vane pump. A slow reving piston or diaphragm pump might not have so much of an issue. I don't have either so I probably won't use my heat exchanger at this stage.

From the above pieces advice I might go for an immersion coil running cold water.

When the learning stops the fun stops, so I am definately having fun.

Thanks all.

[meerkat]

With small fermenters cavitation and NPSHa could be a problem. The pump around system that I mentioned above was with fermenters over 10 m tall, so there was no cavitation problem. I have seen 80 m³ fermenters that had water sparge rings on the top that simply sprayed water onto the outside of the fermenter to take advantage of the evaporative cooling as the water ran down the sides of the fermenters into a return gutter. These fermenters were in an open-sided building, so the wind was able to help with the cooling.

Coils inside the fermenter can work well because the CO₂ bubble generation induces a natural mixing and the movement over the coil surface increases the heat transfer coefficient. At an industrial scale getting sufficient area in a coil would be much more expensive than an external heat exchanger, but the smaller the fermenters the more economics would favor coils.

[PeteB]

Passive evaporative cooling, Before domestic refrigeration that was a very common practice in Australia, a wooden frame covered with hessian (burlap) and a water trough on the top that wicked the water down the sides. They were called Coolgardie Safes.

I did use that technique last summer but thought pumping through the heat exchanger might be neater

[miller]

Thats exactly how we cool our fermentation tanks , I suggest you try and keep your mash below 30 degrees C to avoid off flavors. We have seen off flavors which can be difficult to distill out when temperatures reach 35 degrees C.

There is enough CO2 in the fermenter so you need not worry about over oxygenating because of the splash.

[MG Thermal Consulting]

Meerkat has pretty much encapsulated many heat transfer issues- as scale of equipment increases what works as cooling in a small scale doesn't work on a large scale.

At some point using jacketed exchangers become less efficient and you have to lower the water/glycol temperature in the "grey area" where you can get close to the required heat transfer with agitation.

Of course the cost is more HP for the cooling as a function of the refrigeration cycle needing more energy to perform at colder temperatures.