I wanted to add some more discussion on my recent challenges with poor mash efficiency on my newer Spike 20G All in One bottom drain system. I use a false bottom grid from Brew Hardware which sets my mash dead volume at 5gals (just above the heating element), along with a 400 micron brew bag. I continuously recirculate with splitting the pump return at both the whirlpool port and also into a lineloc through the lid into the top of the bag. I set my mill at 0.025" so my grains are crushed really well with a reasonable amount of flour too (husks all appear to be very well crushed). There is a thermowell that I have a secondary temp confirmation as well as occasional thermopen verification in the top of the mash area. I am getting a slow ramp up to OG, where in the last batch I kept mashing for over two hours going up a few points every 15 mins and I even shut off the whirlpool valve to push more through the bag. I took a measurement of the kettle at the end of this time showing 11.8 brix (1.048). My NEIPA recipe called for an OG of 1.067 so quite a bit low. Then I gave up, allowed the bag to gravity drain with the same 1.048. I decided to then squeeze the bag and saw kettle gravity rise some to 1.049. All along the mash pH was a little high at 5.5. This puts me at a mash efficiency (from BS) at 74%.
Question - Is this the mash extraction efficiency that most others are getting from full volume BIAB?
74% mash efficiency is well within the expected range for full volume, no-sparge mashing. If you provide your grain bill weight, strike water volume, and pre-boil volume, I can use my spreadsheet (linked in my previous post above) to tell you what the best you could expect was, and where you may have lost efficiency.
1. Are grains not releasing sugars unless the bag is compressed. Wouldn't the recirculated liquid be homogeneous and therefore the only gain from compression would be added volume of same gravity wort?
There is likely higher gravity wort in, and near the surface of, the grits during the mash. Given enough time and/or agitation, this higher gravity wort will homogenize with the bulk of the wort. Squeezing should not produce higher SG wort
if the conversion and homogenization was complete before squeezing commenced. Additional conversion after the initial drain can cause the squeezed wort to have a higher SG, as can incomplete homogenization.
2. Is there an effect of reduced extraction when all of the liquid is not in direct contact with the grains, when a false bottom is used? Even though there is continuous recirculation? Especially when the false bottom may be half of total recipe liquid.
Depends on the flow pattern, and whether or not you have channeling during recirculation. In a system with a center bottom drain, there
may be little to no flow under the false bottom near the vessel walls. If this is occurring, then the wort retained due to grain absorption will have a higher gravity than if all the wort were properly homogenized. Higher SG wort absorbed by the grain means more sugar retained with the grain and that results in lower lauter and mash efficiency.
3. Does a too aggressive recirc flow rate result in lower mash extraction efficiency? Note that I have a poor mans sight glass by vertically running a hose from the racking port, with marked volumes showing that my levels below the bag do not change
Not by itself, although too high a recirculation rate can result in flow channeling in the grain bed and failure to fully homogenize the wort, with results as discussed above.
Brew on
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