Infusion Step
Hot water needed to reach the next rest temperature
Fast Probe Thermometer: Infusion maths is only as good as the temperature reading. A quick, accurate probe beats a dial thermometer lagging a degree behind the mash.As an Amazon Associate we earn from qualifying purchases.
View on AmazonHow This Is Calculated
The calculator uses the standard infusion equation from Palmer's How to Brew, in metric form:
The bracketed term is the thermal mass of the mash expressed as litres of water: dry grain carries about 0.4 times the heat capacity of water per kilogram, which becomes the 0.41 L per kg constant in metric units. The same constant drives the strike temperature in the Grain Bill Calculator, so a plan built there steps consistently here.
The denominator is why hotter infusion water means less of it: water at 98°C has 34 degrees of useful heat above a 64°C target, while 80°C water has only 16, roughly doubling the volume required. The calculator reports the addition and the new total mash volume so you can check it against your tun.
Typical Step Schedule for a Whiskey Mash
Most all-grain whiskey mashes need only a single saccharification rest at 64 to 68°C, which the strike water reaches directly. Steps come in when you dough in cooler on purpose: a 50°C rest helps with high-protein or flaked grain, and stepping up afterwards with boiling water avoids direct heat and the scorching risk that comes with it.
A practical sequence: dough in at 50°C, rest 20 minutes, infuse to 64°C for the main conversion, and optionally infuse again to 76°C for a mashout before lautering. Chain the calculator: after each addition, the new total water becomes the mash water for the next step. Check conversion is on track with the Refractometer Calculator, and see the Mash Temperature Guide for what each enzyme rest actually does.
Mind the practical ceiling: every addition dilutes the mash. If the tun is close to full, a thicker dough-in or direct-heat step is the alternative.
Worked Example
A 5 kg whiskey mash doughs in with 13 L of strike water at 50°C for a short protein rest. To step it to 64°C with just-boiled water at 98°C:
After the addition the mash holds 19.2 L at 64°C, a thickness of 3.8 L per kg, comfortably in conversion territory. For a mashout the same maths runs again with the new water volume: stepping 19.2 L from 64 to 76°C takes about 11.5 L more, which is why mashouts by infusion demand a roomy tun, and why many distillers stop at the saccharification rest instead.
Real tuns lose a degree or so to the vessel walls and lid, more if the tun started cold. Preheating with a couple of litres of hot water before dough-in, then discarding it, makes the equation land noticeably closer.
Rest Temperatures and What They Do
Each rest favours a different enzyme system, so a step schedule is really a set of choices about wash character:
45 to 55°C, protein rest. Protease activity breaks longer proteins into yeast-usable amino acids. Worth 15 to 20 minutes for mashes heavy in flaked or unmalted grain; skippable for well-modified malt.
60 to 65°C, beta-amylase range. Produces the most fermentable wort, which for a distilling wash means the most alcohol per kilogram of grain. The usual single-rest target for whiskey mashes sits here at 64°C.
68 to 72°C, alpha-amylase range. Converts faster but leaves more unfermentable dextrins. Useful for beer body; mostly a disadvantage in a wash headed for the still.
76 to 78°C, mashout. Ends enzyme activity and thins the mash for lautering. Above 78°C tannin extraction picks up, which is why the calculator warns there.
The Mash Temperature Guide covers the enzyme chemistry in depth, and the Corn Mash Recipe shows a full schedule in practice.