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Old 03-06-2009, 01:48 PM   #1
The Blow Leprechaun
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Default Layering Beer Mechanism

I debated putting this here or under general techniques, so if someone wants to move this thread or something, I'm not going to be offended! It seemed more like a chemistry/physics-ish question to me than a technique one... I know how to pour a layered drink, I'm more curious about the science of it.

My question is this: when layering a drink, which matters more - final gravity or alcohol percentage?

It seems to me that final gravity would be the deciding factor because it's strictly a measure of density (right?), so as long as your highest FG was on the bottom, it should layer.

Follow-up question: do you need an appreciably different density to get it to form a clear layer, or does the similarity influence just the difficulty of getting a layer to form? If so, any guesses on how much?

I'm asking because I'm thinking about brewing two beers designed to be layered on each other, and trying to think how to approach it to get it the way I want it.

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Old 03-06-2009, 02:29 PM   #2
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Yes, it is the final gravity (density) that is important, not the alcohol content

As to how much difference, that depends on your level of sobriety. If one were really careful, you could layer two liquids with the same gravity. The bigger the difference in the gravities, the easier it is to layer. I like to cheat with layered shots and use a 10 ml pipette.

As to the actual detailed mechanism of this maybe a physicist will chime in

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Old 03-06-2009, 02:37 PM   #3
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Alcohol is completely and readily soluble in water (or beer for that matter). However, if you poured straight ETOH into water, it will initially rest at the top because it is less dense than water. But it will dissolve so rapidly that this isn't worth considering. So, IOW, alcohol is not much of a factor when mixing beers of different densities.

A lower FG beer will "float" on top of a higher FG beer due to differences in density and the fact that the compounds which cause SRM (color) aren't as soluble as alcohol is soluble. The greater the difference in density, the more quickly and dramatically they will separate. I imagine even a slight difference in density will eventually cause them to completely separate. However, I don't really mix beer (Black and Tan), so I don't have much first-hand experience with it.

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Old 03-06-2009, 05:54 PM   #4
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This sounds pretty much like what I thought... now I think I'll need to do some experimentation on styles of beer that go well layered together beyond the basic black and tan.

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Old 03-08-2009, 01:23 AM   #5
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Another tip for pouring a black and tan (if you don't want to wait a long time for them to separate, which happens if the SGs are not drastically different) is to pour the higher SG beer first, then pour the lower SG beer on top, over a spoon. This disperses the beer and keeps it from falling too deeply into the higher SG beer, allowing the separation to complete sooner.

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Old 03-08-2009, 07:32 AM   #6
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I have something like this laying around here somewhere..

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Old 03-08-2009, 07:33 AM   #7
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Quote:
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I have something like this laying around here somewhere..
Yeah, I have a spoon too.
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Old 03-08-2009, 08:03 AM   #8
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I had a spoon once but Steve Martin got it in the divorce. And that lamp. and that chair. He let me keep s&^thead the dog.

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Old 03-09-2009, 04:11 PM   #9
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Gravity is the major factor, but carbonation plays a roll in this as well. Take the classic black & tan for example. The carbonation in the Bass is much greater and continuall pushes up. I used to work for Guinness (prior to the Diageo era) and was directly responsible for assisting local customers in setting and balancing there draft system. One of the biggest challenges we had was with the pour on the Bass. If it was not pouring correctly, and foaming too much (or too little in the case of long-draw) it was nearly impossible to get the Guinnes to "float" correctly. You would see the bottom of the Guinness slowly falling into the Bass. Once we either corrected pressure, or changed line lengths, the problem would go away. If the temps aren't correct it can be problematic as well as that wil affect the amount of dissolved CO2 in the beer.

Guinness is lighter in calories and alcohol than most popular beers that would be layered with it. That said, gas does still play a big rol in the finished product.

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Old 03-09-2009, 04:17 PM   #10
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Another thought, when beer lines aren't cleaned properly and beer stone build up gets to be pretty thick, it would cause problems as well. I am not 100% sure as to why, but I think I remember something along the lines of dissolved solids being out of whack in the product coming out of the faucet.

Brolly spoons are a great aid in pouring black & tans. I have seen bartenders just try to pull gently on the guinness tap when they didn't have a spoon to keep the beer from shooting down into the bass. The problem here is that the Guinness isn't being forced the restrictor plate w/ enough force to effectively agitate dissolved gas, resulting in a metallic after taste in the Guinness and an incorrect mouthfeel.

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