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Layering Beer Mechanism

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The Blow Leprechaun

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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.
 

pjj2ba

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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
 

menschmaschine

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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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The Blow Leprechaun

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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.
 

nibiyabi

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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.
 

dontman

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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.
 

McSwiggin'

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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.
 

McSwiggin'

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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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The Blow Leprechaun

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I didn't even think about carbonation.

I think I'll just try to and design these beers to be carbonated to the same level, or maybe have decreasing carbonation as the gravities get lower.
 

McSwiggin'

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I didn't even think about carbonation.

I think I'll just try to and design these beers to be carbonated to the same level, or maybe have decreasing carbonation as the gravities get lower.
I don't think the issue is so much having lower carbonation in the lower gravity beer, more that it is not having a flat or over-carbonated beer on the bottom. The beer on the bottom needs to retain most of it's gas and at the same time not be too "heady".
 

McSwiggin'

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Carbonation doesn't really matter. It's easy to see that yourself: You can let the Bass and/or Guinness go completely flat and it doesn't affect how hard it is to pour a black and tan. It's all about the density (ie specific gravity).
I don't know that I agree with you on this. I know specific gravity is the major contributing force behind it, but we had many problems over the years, mostly with long draw systems that wern't balanced properly. We worked pretty closely with Guinness to on these issues (in the days prior to Deagio). Once we replaced lines for proper resistance, or adjusted psi output on the regulators, the problems went away. I estimate 30 - 40 accounts with similar problems over the years that Guinness was consulted on, and I trust those guys new what they were talking about.

Are you talking about pouring from a bottle or can? There is a lot less force when pouring a beer from bottle or can rather than dispensing from a keg. I have never seen a keg of Bass or Guinness go flat while pressurized by a dispensing system so I have no comparison there.

I don't dispute the fact that different gravities will layer regardless of carbonation, but I do know from experience that it is harder to keep them from "mixing" if there is not enough upward pressure from the bottom layer, specifically when poured from a pressurized system through a creamer faucet which, when set up correctly, does come out at a considerable force. The spoon can only disperse so much of the force.
 
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