Thursday, May 31, 2012

Maximizing wort extraction from BIAB

One of my frustrations with the BIAB method is that once mashing is complete, I feel that too much of the wort remains in the bag.  And even though a "stuck sparge" is supposed to be impossible with BIAB, there sure does seem to be too much sweet wort trapped in the grain bag that is unaffected by gravity while it hangs above my keggle.

I've tried spinning the bag to squeeze wort out, and I've put the grain bag in a collander on my keggle and tried to push on it and squeeze as much out as possible without burning my hands.  With either of these methods I can usually hit my numbers, but I'd like to figure out a way to avoid all the squeezing, pressing, etc.

I referred back to John Plamer's How to Brew book to try and get a scientific explanation of the sparging/lautering.  Appendix F of the book discusses the fluid dynamics of water through a traditional cooler mash tun grain bed.  In this case, the grain bed is only being affected by the downward force of gravity.  There is no lateral force on the sides of the grain bed, so the flow resistance is determined solely by the weight of the sparge water flowing through it, and the weight of the grain bed itself.

For BIAB method however, the grain bed/bag is also subjected to the lateral pressures of the grain bag itself, which push the grain particle closer together, increasing the flow resistance for the wort.

To prevent this, I plan to use a cake rack (or similar) to prevent the bag from collapsing around the grain bed as the bag is pulled from the vessel.  I have not determined if placing the rack inside the bag or under the bag is best.

I'm hoping to try this in the next week when I brew up a Gumballhead clone.  I'll report back my findings.

In the meantime, please let me know your thoughts on this and any other ideas you have to allow wort to flow more freely from the bag.


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How about recirculating or vorlaufing wort through the bag whilst it hangs as well? Or Dunking it into a second pot of water for a second sparge?

Good questions. I have tried both methods you mention with limited success. I usually vorlauf during the mash to even out the temperature in the grain bag, but not to get the wort to drain. Once I tried the dunking method also, but my goal is to try and keep things simple, so I decided to drop that.

I mentioned in this post that I wanted to avoid squeezing, but that's what I've found works best. I wrote about this in this post:

It does not add any astringency to the beer, and does a great job of getting a great deal of the wort out of the grains. I have shot some video of this method and plan to post it when I get some free time (and figure out how to use MoveieMaker!).

The other key to maximizing wort extraction is to choose the right bag material. While most BIAB'ers have success with voile, I tried that but am leaning to paint strainer bags that seem to have slightly more open weave that really lets the wort drain well. Keep your eyes peeled for a post discussing that here as well!


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