Vessel diagram
Fill level shown as a proportion of each vessel's capacity; colour reflects ABV.
Run charts
Updated live while running.
How a thumper (retort) works
A thumper — also called a retort — is a sealed intermediate vessel connected between the boiler and the condenser. Vapor from the boiler bubbles up through liquid sitting in the thumper before continuing on to the condenser (or a second thumper). This does two things at once: it transfers heat into the thumper's liquid, and it strips some ethanol out of the passing vapor while picking up ethanol from whatever is already in the thumper — effectively adding a genuine extra distillation stage without a second heating element, run, or fire.
The catch is that a thumper has no direct temperature control of its own (unless you choose to heat it directly). While it's still cold, all the incoming vapor condenses into it — meaning it fills. Once it reaches its own bubble point, it starts producing vapor of its own and can begin to drain — but only if its own vapor output is faster than the rate the boiler is condensing into it. Whether a thumper ultimately fills, empties, or overflows partway through depends on the boiler's vapor rate, the thumper's size, its starting charge, and whether it's heated. This simulator models that balance directly rather than assuming a fixed outcome.
A note on scope: this simulator uses a single lumped heat-loss coefficient per vessel (same simplified model as the ambient/insulation setting in the pot still simulator) rather than modelling heat transfer through each specific surface (hotplate, vapor-filled headspace, liquid-filled walls) individually. It captures the real fill/drain/overflow dynamics correctly, but is not a claim to that level of surface-by-surface detail.
Detailed calculation model
1. Boiler
Identical physics to the pot still simulator: Van Laar VLE, Antoine vapour pressures, a bisection bubble-point solve against your local atmospheric pressure, and an energy-balance vapour rate once at rolling boil.
2. Thumper mass and energy input
Vapour arriving from upstream condenses into the thumper's liquid, adding its volume and releasing its latent heat (ethanol 841 kJ/kg, water 2260 kJ/kg, weighted by composition) as the thumper's primary heat source. An optional direct heating element adds further power on top.
3. Two-phase behaviour
Below its own bubble point, all available energy raises the thumper's temperature (thermal-mass heat-up, same equation form as the boiler) while its liquid volume only grows. At or above its own bubble point, temperature tracks the equilibrium value and any energy surplus vaporises the thumper's own liquid via the same VLE and energy-balance approach as the boiler — a genuine second equilibrium stage, not a fixed multiplier.
4. Overflow and dry-boil detection
Each vessel has a set capacity. If accumulated liquid would exceed it, the run flags an overflow. If a directly-heated vessel's liquid volume approaches zero while still receiving heating power, the run flags a dry-boil risk. Both are checked every step, not estimated after the fact.
Chaining is sequential: the boiler's output becomes thumper 1's input; thumper 1's output becomes thumper 2's input (if enabled) or the condenser's input otherwise. Ambient temperature, insulation, thermometer error and atmospheric pressure apply to every vessel the same way they do in the pot still simulator.
Building a thumper setup? A dedicated distilling thermometer with a fast response time makes it much easier to catch a thumper approaching its own bubble point in real time.