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:

1. Starting with 2L more than me at the mash stage.
2. Starting the boil with 2L less than me (28L vs 30L).
3. Calculating 0.8L of grain absorption rather than my simple 1L per kg.