Diffusion vs. Density

[jack13]

I just poured 12 oz of coffee into my 5 gallon fermenter, which has been aging an imperial stout (now an imperial coffee stout, I suppose!).

I think the FG is 1.020 or so.

Can I expect the coffee to diffuse evenly throughout the fermenter, or will it sit on top since it's (a lot?) less dense? I'll shake or stir if I need to, but would just as soon avoid that. Since it's aging so long I'm a bit more paranoid about oxidation than I'd usually be.

 

[ajdelange]

Eventually it will diffuse but it may take a long time. Color isn't going to help you here. As a guide you could put 5 gal of plain water into a spare fermenter and pour 12 Oz of coffee into that. It will diffuse at about the same rate. If you want to model the density differences dissolve enough sugar into the water to make the SG of the mix about the same as the FG of the stout..

 

[IslandLizard]

What kind of fermentor are you using? How large is the headspace?
Do you have access to CO2?
Is this going to be bottled or kegged?

 

[jack13]

What kind of fermentor are you using? How large is the headspace?
Do you have access to CO2?
Is this going to be bottled or kegged?

It's a glass carboy. Not much headspace, maybe 1/4 gallon.

I do have CO2, and it'll be kegged.

You saying fill headspace w CO2 and stir?

 

[burntchef]

Hi!
Where are you in the small wonder? I am in Georgetown. Looking to network with local home brewers.
Eric

 

[jack13]

Hi!
Where are you in the small wonder? I am in Georgetown. Looking to network with local home brewers.
Eric

Just sent private message...

 

[IslandLizard]

It's a glass carboy. Not much headspace, maybe 1/4 gallon.

I do have CO2, and it'll be kegged.

You saying fill headspace w CO2 and stir?

Yup, flush headspace with CO2, stir it gently, and flush again. The back end of that long plastic brew spoon has a little stirring paddle on it.

I condition/age in kegs, under CO2. It also carbonates somewhat at the same time. That way it can sit for months at cellar temps (usually a bit higher), and I can add anything anytime, easy to mix, and never worry about oxidation. Those are my "secondaries," and the content never smells any oxygen.

 

[jack13]

Eventually it will diffuse but it may take a long time. Color isn't going to help you here. As a guide you could put 5 gal of plain water into a spare fermenter and pour 12 Oz of coffee into that. It will diffuse at about the same rate. If you want to model the density differences dissolve enough sugar into the water to make the SG of the mix about the same as the FG of the stout..

Good idea! I'm being lazy right now, but that is something I will definitely do some day when I'm in the mood. Do you see any problem with scaling it down (e.g., 1 gallon of 1.020 sugar water and 2.4 ounces of coffee)?

 

[ajdelange]

It is obviously going to take longer to diffuse the height of a longer column that a shorter one. Other than that, no. A further thought is to try to pour the coffee from some height so that it plunges into the beer this getting partly mixed when added and leaving less to the diffusion process.