Mash water calculation for the Robobrew
Dedicated brewers will spend years fine-tuning their mash-in water volume and grain crush to get optimal efficiency and clarify, but for most Robobrewers purchasing pre-milled grain from a local homebrew supplier, there’s a few formulae that will give you great efficiency and reduce the chances of a stuck sparge right off the bat.
When recirculating, the trick is to have a nice liquid mash without the weight of the water and grain pressing down on the malt pipe screens hard enough to cause blockages.
3 litres per kilogram
This formula is pretty easy. For every kilogram of grain, add three litres of water:
<Grain Bill, kg> × 3
For a typical 5kg grain bill this means 15L of water for your mash in.
5 × 3 = 15Lmash water
The Grainfather formula
Instructions for the Grainfather use a slightly more complicated formula. Because the RoboBrew and Grainfather have very similar dimensions, the physics of the recirculating mash are very similar.
( <Grain Bill, kg> × 2.7 ) + 3.5
For a 5kg grain bill, this is:
(5 × 2.7) + 3.5 = 17L mash water
Make up the difference in the sparge
I personally sparge until I reach almost around 29-30L mark without much care about target gravity readings. To achieve this I make sure I have about 20L of hot water ready to go, knowing I won’t use it all. The grain will absorb about 5L of water (1L per kg), so 10L+20L = 30L final volume.
Yet again Grainfather offer a nice formula for calculating this.
((<Target Fermenter Volume, L> + <Loss to Boil and Trub, L>) – <Mash Volume,L>) + (<Grain Bill, kg> × 0.8)
With the aforementioned 5kg grain bill and a target volume in the fermenter of 23L, we get:
((23 + 5) – 17) + (5 × 0.8) = 15L sparge water
The large 5L difference between my lazy fill-to-30L method and Grainfather’s calculated method comes down to a few things:
- Starting with 2L more than me at the mash stage.
- Starting the boil with 2L less than me (28L vs 30L).
- Calculating 0.8L of grain absorption rather than my simple 1L per kg.