Author Topic: Is pressure-filtering ok to extract wort from mash?  (Read 1901 times)

Offline Silicon

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Is pressure-filtering ok to extract wort from mash?
« on: December 22, 2017, 01:32:16 PM »
I could really use some brainstorming advice from you all-grain brewers. :)

I'm currently an extract brewer and reading all I can on all-grain principles.  I'm wondering if anybody has any information regarding extracting wort from mash using a filter under pressure rather than sparging?  (Think of a coffee French press...pressing a filter against the mash to separate-out the liquid.)  I'm trying to determine if there are any detrimental issues I need to watch out for.  I'm hopeful that I can avoid them with some ingenuity...


Offline Oginme

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Re: Is pressure-filtering ok to extract wort from mash?
« Reply #1 on: December 22, 2017, 02:07:54 PM »
Under pressure is a great way to get a stuck mash (unable to drain).  When the starches are extracted from the grain kernels, they become very soft and malleable.  Applying pressure is a great way for them to get pushed into the void areas of the husk/grain filter bed and cause blockage.  It reminds me of a ChemE lab I once took where we had to try different media in an extraction column and then try to speed up the rate of flow by altering the process variables.  The spout from the top of the column when the pressure safety valve went off was spectacular.
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Offline Silicon

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Re: Is pressure-filtering ok to extract wort from mash?
« Reply #2 on: December 22, 2017, 02:58:46 PM »
So the mash would actually clog any sort of filter?  If so, that'd imply that the mash must remain loose for sparge water to flow through it.  I know trying to do it with a simple, single valve outlet would majorly fail, but I'm thinking of something more like a French press (i.e. press a filter against the mash) or a cider press.  (A cider press is a great example as it has to mash apples which are extremely hard.)  I'd also thought of something akin to a BIAB with a twist-squeeze of the mesh bag.

I'm thinking more of any chemical reasons why extracting the wort under pressure might be bad, e.g. extra tannins, maybe?

Offline Oginme

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Re: Is pressure-filtering ok to extract wort from mash?
« Reply #3 on: December 22, 2017, 05:12:30 PM »
Chemically, it takes conditions of pH over 6 and heat over 170?F (or there abouts) to solubilize tannins.  Pressure could result in lowering the heat requirement, but I don't know (nor have I looked) at any research on that topic.

When draining the wort from the grains, the first thing you do is start the drain slowly.  This allows the husks and larger kernel particles to form a filter bed through which the finer particles will get trapped.  The presence of hulls is the real key, as they act as channels for the wort to flow down through the every increasing depth of spent grains.  Shred the hulls too much, such as in a congress mash, and there is no chance of making a filter bed to drain the wort efficiently.

When you drain the wort too fast at the start, it compresses the filter bed quickly and removes the void areas which allow the wort to flow. 

Now, go back to the french press idea.  The filter is on the top, where most of the finer particles will settle.  Press a filter or fine mesh against it and apply pressure and you will quickly compress the finer particles against the filter, thus cutting down on the void areas and ceasing the flow of wort.

A cider press works on a different principal.  There are gaps between the boards which allows the juices to flow out through the sides as well as the bottom.  The grain of the wood also helps in channeling the juices away from the pulp.

As someone who does mostly BIAB, most people allow some or most of the wort to drain first.  When you twist of squeeze the bag, there is areas along the whole surface of the bag for the wort to drain, so it takes the least resistant path out of the grains and bag.  Oh, and yes, the bag can be blinded over and stop wort flow out.  I had one early recipe of 50% rye malt (hull less) and flaked rye which I started squeezing much too early and ended up with a gummy mess on the outside of the bag and missing my kettle volume by a fair amount due to the entrained water left in the grains.

I can think of a number of reasons why it might not work, but the proof is in the results.  By all means try it.  As someone who works in product development, you never really know until you try if you missed something or not -- it just boils down to probability of success versus effort input.

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Offline brewfun

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Re: Is pressure-filtering ok to extract wort from mash?
« Reply #4 on: December 23, 2017, 11:20:39 AM »
So the mash would actually clog any sort of filter? 

Commercially, there are mash filter systems that work similar to a cider press. The mash isn't compressed, but is held vertically between two plates at a depth of about 4". Unlike a cider press where the pulp is squeezed to extract the juice from cells, the mash isn't compressed but quickly sparged to extract the sugar. The resulting cake does get squeezed to remove water, making it easier to move on a conveyor for disposal, but the gravity is too low for reuse.

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If so, that'd imply that the mash must remain loose for sparge water to flow through it. 

Sugar extraction from grain is about osmotic pressure. Without new water flow, the extraction stops at equilibrium. Mechanical compression of the grain will force not only sugars into the water, but proteins, glucans, cellulose and tannins.

On a horizontal plane, the weight of the water can compress the grain, slowing or stopping flow. This also slows or stops efficient osmotic gradients within the mash bed. One cure for this is using mash rakes to increase the surface area available to water. Another cure is to not have too much water above the grain bed. Narziss did loads of research about wort velocity, the sum of which is that you really don't want more than 2 column inch pressure differences between the mash and the exit velocities. The practical application of his reasearch is that optimal sparge depths in commercial systems don't exceed 24". Deeper mash beds lose efficiency and speed.

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I'm thinking more of any chemical reasons why extracting the wort under pressure might be bad, e.g. extra tannins, maybe?

I'd add in haze issues and perhaps oxidation, but I think the mechanical reasons have more relevance. Tannin extraction is related to the amount of husk edge surface area as well as pH, temperature and sugar density (gravity). Luckily, malt does everything it can to become beer by creating the chemistry for us, if we give it the right mechanical conditions. 
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