Getting sick back from fermenter and not crash cooling

[brewhaus88]

Hello,

This is the first time I’ve used my temperature coil in my conical. I seem to be getting some suck back from the fermenter but I just started fermentation. I’ve heard this happening during crash cooling but never during primary fermentation. The cooling water is at 34 degrees. (Added a little to much ice and had fridge way colder) it only wants to suck back when the pump turns on and recirc’s the cold water through the coil.

For now I have just put in a blowoff tube that goes to the floor and turned down the fridge to warm the water up a bit.

I would like to know if anyone has seen this behavior with cooling water evening too cold. How did you counter act this?

 

[Dgallo]

Hello,

This is the first time I’ve used my temperature coil in my conical. I seem to be getting some suck back from the fermenter but I just started fermentation. I’ve heard this happening during crash cooling but never during primary fermentation. The cooling water is at 34 degrees. (Added a little to much ice and had fridge way colder) it only wants to suck back when the pump turns on and recirc’s the cold water through the coil.

For now I have just put in a blowoff tube that goes to the floor and turned down the fridge to warm the water up a bit.

I would like to know if anyone has seen this behavior with cooling water evening too cold. How did you counter act this?

So your cooling you’re wort to pitching temps in the conical FV with submersion coils that draw 34*f water through it with a pump?

 

[brewhaus88]

Well technically I’m maintaining my fermentation temp but yes, I have already pitched the yeast but it hadn’t started active fermentation yet. When I woke up this morning to check on it, fermentation had begun and isn’t sucking back anymore so problem solved for now.

 

[Dgallo]

Alright. I figure it’s because the cold water running through the coils creating some convection. It is also dropping the temp of wort below room temp which will cause negative pressure and suck back since it’s cooling quickly

 

[mongoose33]

When I'm lowering temps in my conical, bubbling through the airlock jar stops when the pump goes on. It's the coil cooling the headspace gases, which reduces the pressure, and which induces suckback. Ideal Gas Law, I think, but don't quote me on that. The larger the headspace, the more the cooling coils are exposed to that headspace, the greater effect you'll have.

I'm fermenting right now--just dropped the temp from 66 to 64. Guess what happened when I did that? Bubbling in the airlock jar ceased. It's back to bubbling now.

 

[Vale71]

This is entirely normal and inevitable and due to the air in the headspace shrinking as it cools in accordance with Boyle's law. If your blow-off tube is long enough this should not be a problem as the effect is not strong enough to actually suck water all the way to the top of the fermenter (for every centimeter of lift you need about 1 mbar of vacuum).

 

[brewhaus88]

Alright. I figure it’s because the cold water running through the coils creating some convection. It is also dropping the temp of wort below room temp which will cause negative pressure and suck back since it’s cooling quickly

Ah never thought about that. Thanks for the reply!

 

[Vale71]

Ah never thought about that. Thanks for the reply!

Stop thinking about it right now. Convection does not lower pressure and does not create suckback.

 

[Dgallo]

Stop thinking about it right now. Convection does not lower pressure and does not create suckback.

Convection from the air cooling near the exposed coils causes that colder air to sink and the the negative pressure created by the temperature dropping would all work in tandem causing the suck back

 

[Vale71]

No it won't as sinking air is always replaced by an equal volume of rising air without causing any change in pressure neither local nor global as nature simply abhors a vacuum. It's really just the application of gas laws combined with the fact that air cools much faster than wort/beer causing the air in the headspace to experience a much more marked drop in temperature than the underlying wort.

Here is an example just to give an idea of how much a drop of 2°C means in terms of pressure drop. Let's assume 1013 mbar inital pressure (atmospheric standard) and initial temperature of 293.15°K (22°C) and a final temperature of 291.15°K(20°C).

Assuming volume and gas quantity remain constant (no fermentation yet) we apply the equation:

P1/T1=P2/T2

and we obtain

1013/293.15=P2/291.15

which becomes

P2=1013/293.15*291.15

and finally

P2=1006.1 mbar

That's a drop of nearly 7 mbar, this would cause water to be sucked in the blow-off tube approximately 7 centimeters high. And that's just from the air in the headspace cooling by 2°C, the wort/beer doesn't even need to cool by even a tiny bit as volume contraction in liquid is way smaller than in gases and it only plays a (secondary) role for large temperature differences.

And yes, if you don't like the metric units that is entirely your problem.

 

[Dgallo]

No it won't as sinking air is always replaced by an equal volume of rising air without causing any change in pressure neither local nor global as nature simply abhors a vacuum. It's really just the application of gas laws combined with the fact that air cools much faster than wort/beer causing the air in the headspace to experience a much more marked drop in temperature than the underlying wort.

Here is an example just to give an idea of how much a drop of 2°C means in terms of pressure drop. Let's assume 1013 mbar inital pressure (atmospheric standard) and initial temperature of 293.15°K (22°C) and a final temperature of 291.15°K(20°C).

Assuming volume and gas quantity remain constant (no fermentation yet) we apply the equation:

P1/T1=P2/T2

and we obtain

1013/293.15=P2/291.15

which becomes

P2=1013/293.15*291.15

and finally

P2=1006.1 mbar

That's a drop of nearly 7 mbar, this would cause water to be sucked in the blow-off tube approximately 7 centimeters high. And that's just from the air in the headspace cooling by 2°C, the wort/beer doesn't even need to cool by even a tiny bit as volume contraction in liquid is way smaller than in gases and it only plays a (secondary) role for large temperature differences.

And yes, if you don't like the metric units that is entirely your problem.

Anytime that gases or fluids moves due to density(cold air being high pressure)it is considered convection. I’m not saying your wrong about the law of gases, but the law of gases can not take place without convection. The movement of the molecules is due ti convection. The degree to how densely they constrict or wildly expand is due to temperature and as a result positive or negative pressure is create