False-bottoms and efficiency

The common opinion seems to be the higher the false-bottom (i.e. the more foundation-water space beneath the false bottom), the worse the efficiency. What doesn't make sense to me though is if I were to vorleuf the same amount of volume of the foundation-water, wouldn't that eliminate this idea of false-bottoms being less efficient? i.e. if I have one gallon of space under my false-bottom, and I vorleuf at least one gallon of the first runnings, have I eliminated any issue with the false-bottom efficiency? I guess I need a better understanding of this.

Not sure of the science but I have a adventures in brewing keggle with false bottom that has 2.5 gallons before it touches the grain bed, and my beer smith efficiency is always above 75 percent. I would think during mash heavier sugars would sink below the screen and during fly sparge it would filter out the good stuff better. But maybe a self taught pro can explain.

Jamming said:

Not sure of the science but I have a adventures in brewing keggle with false bottom that has 2.5 gallons before it touches the grain bed.

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I have the same bottom and hit 84% eff. every time.
I also have a center bottom drain and a pump to recirculate during mash
but I'm sure a dip tube would do the same thing.
Jamming, you can get the base water down to about 2 gallons if you take a grinder and round off those bottom support braces.

I need to bump this thread. I am having similar issues, only there's 3 gallons under my false bottom! I recirculate the entire mash with a low heat direct fire to maintain mash temps. Maybe I'm missing something, but wouldn't the added strike water bring your efficiency down? In theory, since you aren't using as much sparge water, you aren't rinsing your grains as effectively as you would if you didn't have a large amount of space under the fb. Maybe I'm lautering & sparging too fast? Any thoughts?

I have about 1.5 gallons under my false bottom and I have found a range of efficiencies as I try to lock down my process. I don't have a pump, but using a manual vorlauf, a mash out and fly sparge, I have my efficiency up to 85%. I fly sparge very slowly and it always takes about 75 minutes for me to collect 7.5-8 gallons of wort. I think speed is a big factor.

The efficiency problem only exists when you have a false bottom without a dip tube. Then, it's dead space filled with unrecoverable wort, and that will of course reduce efficiency.

If you have a tube that goes through the false bottom and pulls the wort from there, the false bottom should not effect efficiency at all.

My dip tube sits below my false bottom. I have no problem collecting my wort. My problem lies in collecting a higher volume of wort at a lower gravity. I assumed that the problem lies in the extra 3 gallons of strike water added to the mash tun to achieve a proper level of water in contact with the grain. Am I wrong in doing this? Perhaps I am sparging too quickly or I am channeling on my return valve?

passedpawn said:

The efficiency problem only exists when you have a false bottom without a dip tube. Then, it's dead space filled with unrecoverable wort, and that will of course reduce efficiency.

If you have a tube that goes through the false bottom and pulls the wort from there, the false bottom should not effect efficiency at all.

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+1

My efficiency went up 8% when I added a dip tube. Before that the heavier wort just sits below the take off valve.

It doesn't work that way because the water on the bottom is actually the most dense (has the highest gravity). This is why it is down there.

petep1980 said:

It doesn't work that way because the water on the bottom is actually the most dense (has the highest gravity). This is why it is down there.

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I'm not so sure that's entirely true. Sugar, like salt, wants to become "part" of the water; it's a solute (up until the point of supersaturation, http://en.wikipedia.org/wiki/Supersaturation).

In fact here's some references

http://science.jrank.org/pages/6282/Solubility.html
http://kitchenpantryscientist.com/?p=2625

It's my assumption that because the solution hasn't been stirred in order to disperse all sugars that the concentration will be at the lowest point because of gravity. It's not been boiling either so that convection will excite the molecules into dispersing completely.

stamandster said:

I'm not so sure that's entirely true. Sugar, like salt, wants to become "part" of the water; it's a solute (up until the point of supersaturation, http://en.wikipedia.org/wiki/Supersaturation).

In fact here's some references

http://science.jrank.org/pages/6282/Solubility.html
http://kitchenpantryscientist.com/?p=2625

It's my assumption that because the solution hasn't been stirred in order to disperse all sugars that the concentration will be at the lowest point because of gravity. It's not been boiling either so that convection will excite the molecules into dispersing completely.

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The time frame we're looking at here is small enough that a completely homogeneous wort doesn't happen for us. Compare the SG of your first runnings to those those of your last runnings. Even in no mash out, no sparge brewing they are different.

I too have the Adventures in Brewing PICO style false bottom that a few others mentioned.

What helped improved my efficiency on my last few beers was to pre-heat my tun and to fly sparge very slowly. I have hit my numbers each time I have done this.

petep1980 said:

The time frame we're looking at here is small enough that a completely homogeneous wort doesn't happen for us. Compare the SG of your first runnings to those those of your last runnings. Even in no mash out, no sparge brewing they are different.

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I guess that's why we even sparge at all

stamandster said:

I guess that's why we even sparge at all

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We sparge (I think) because after a while the difference in gravity between the grains and the water becomes small enough there is almost no flux between the two of them. When you sparge you're adding low gravity water which will again increase the flux between the grain and the water extracting the most out of the grain.

It's kind of like cooling your wort.

If you have a 200F wort and cool it in bath of 100F, both liquids will eventually reach equilibrium around 150F or so and no heat transfer will occur. Then you have to replace the 150F cooling water with 100F.

I'm sure someone much more detail oriented than me, and smarter, could really get into the physics of the problem. We hear so many chemistry terms for mashing, but I think physics plays a mammoth role in it that we almost never learn about.