I think you meant to say that a mashout (increasing the mash temp)
decreases the viscosity of the wort, as increasing it would slow down the run-off a bit. The effect is not that large however. You can massage the data
here to determine that increasing the temp of a pure sucrose solution from 150°F to 170°F decreases the viscosity by 16%.
If wort behaved like pure sugar solutions, then increasing the temp would indeed lower the viscosity. However, wort is more complex than a simple sugar solution, and the "
Wort and Beer Fining Manual" has this to say:
"Coagulation of mash particles is favoured by an increase in final mash temperature, though this may also increase wort viscosity, which will tend to offset the beneficial effects of coagulation on run off rates."
Also, increasing the maximum possible wort drain rate may not matter when fly sparging, as you usually limit the drain rate to prevent channeling during the sparge.
For batch sparging, a slightly lower drain rate will increase the time to get complete run-off, but how does this increased time compare to the time required to heat to mash-out temp? There is probably no significant net time reduction.
If I wanted to distill the fermented "beer", I would add amyloglucosidase (aka glucoamylase or just gluco) to the fermenter in order to reduce all of the dextrins, and any residual starch, to fermentable sugar, and thus increase my overall yield.
See above comments. Viscosity reduction from a mash-out is minimal at best. If fly sparging, using part of your "sparge" water as a temp increasing infusion, will end up decreasing your lauter efficiency, as you decrease the amount of actual sparge water used.
The only time a mash-out can significantly increase your mash efficiency is if your gelatinization and solubilization of the starches is not complete at the "end" of your mash. If this is the case, then the mash-out basically allows these two processes to continue for an extended time, and at a higher rate because of the increased temp (essentially just increasing your effective mash time.) This will give you more extract in solution, which will raise the SG of the wort in the mash, thus increasing conversion efficiency. If your mash has already completely gelatinized and solubilized all the starch, then a mash-out will not increase the SG of the wort in the mash.
What is detrimental about letting the grain bed temp fall below 60°C (140°F)?
This has in fact been tested experimentally. You can read about the experiment
here. You need to have either done a mash-out, or achieved 100% conversion of starch to soluble extract, in order for a cold sparge to be equivalent to a hot sparge. Otherwise the hot sparge will effectively extend the mash time and create more extract (higher SG.)
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For what they are worth, here are my recommendations w.r.t. mash-out:
- If you are fly sparging, and concerned about limiting the fermentability of your wort, then do a mash-out. If you are not concerned about limiting fermentability, then it doesn't really matter what you do.
- If you are doing batch or no-sparge, then you can get the same effect as a mash out by starting the boil as soon as you have enough run-off to safely start heating to a boil.
Brew on