Pot Still ABV Calculator: Run Simulator and Cuts

The boiler is a closed, well-mixed ethanol–water batch. A differential component balance gives $d(nx)=y^*(x)\,dn$, and hence

This is the Rayleigh equation presented in the IIT ISM laboratory manual, attached source s2, p.56. The equilibrium curve is a shape-preserving cubic interpolation (pchip) of measured 101 kPa data from Susial Badajoz et al. (2026), Table 5, DOI 10.1021/acsomega.6c04827. Two experimental points are withheld from interpolation for reference checks. A pure-water endpoint closes the dilute interval.

Use $s=\ln(x_0/x)$, so the integral becomes $\int_0^s x/(y^*-x)\,ds$. The tool evaluates a 601-point logarithmic composition grid with cumulative trapezoidal integration. Remaining moles are $n=n_0e^{-I}$; distilled moles and ethanol moles follow directly from total and ethanol balances.

At each composition, molar mass is $M=xM_E+(1-x)M_W$ and cooled molar volume is $v=M/\rho(x)$. Density comes from the experimental columns of Khattab et al. (2012), Table 1, attached s1 p.2. Linear interpolation from 293 to 298 K gives 293.15 K (20 °C); pchip interpolates composition. ABV is $100xM_E/(\rho_E v)$. An inverse bisection converts ABV inputs into mole fractions.

The metered collection volume is $V_m=\int v(y^*)\,dD$. Elapsed time is $t=V_m/Q$, where Q is the constant liquid take-off rate inferred from the one-minute collection sample. This permits changing vapour molar flow without assuming a heater energy balance. Cut boundaries use the heads metered volume and the outlet-ABV threshold. Each cut's component amounts are subtracted at its two boundaries; its combined composition determines its cooled volume and average ABV. Pure ethanol inventory closes independently across all cuts and the residue.

• One equilibrium vapour–liquid stage; no reflux, rectification, entrainment, reaction, or noncondensable gas. All vapour is condensed and collected without delay or losses.
• Fixed pressure approximately 101 kPa; binary ethanol and water only. Sugars, salts, acids, methanol, esters, and other congeners are excluded.
• The liquid take-off rate is inferred from a user-entered one-minute volume sample and held constant at its 20 °C volume equivalent. The time axis starts at first collection and excludes heat-up, cooling delays, and warm equipment inventory.
• All ABV and liquid volumes use 20 °C. The boiler drawing uses the cooled equivalent volume, not the thermally expanded hot liquid level. Jar height shows each jar's fraction of its own final volume.
• Heads end at the selected metered volume. Tails start at the selected outlet ABV, after heads. If the threshold is above the initial outlet strength, there may be no hearts; if below the final outlet strength, there may be no tails. Those cases produce explanatory conditions.
• The Rayleigh balance, the logarithmic integration coordinate, and cut component balances are derived here; the VLE and density values are measured source data. Molar masses use 46.06844 g/mol for ethanol and 18.01528 g/mol for water.
• Charge and result volumes use m³ (US switch: ft³); the heads boundary and one-minute sample use cm³ (US switch: in³). The schematic retains explicitly labelled litres for readability.

Use for educational comparisons and process estimates for licensed distilling, not certified alcohol content, excise accounting, product release, or equipment design. Default input range: 1–60% initial ABV, 0.05–20% boiler stop ABV, with stop below charge; educational mole-fraction mode is limited to 0.005–0.6 initially. Runs stop with liquid remaining, not at a dry boiler.

The first measured nonzero VLE point is x=0.011 (roughly 3.4% boiler ABV); lower compositions interpolate toward the pure-water limit. Tail strength and long-run time there have greater model uncertainty. Density measurements are relatively sparse and have systematic differences from reference alcoholometric data. No accuracy claim finer than about one ABV percentage point is made. Numerical resolution is finer than these physical-data limits.

The supplied cut boundaries are illustrative controls, not advice for removing methanol or obtaining a safe or desirable product. Actual cuts depend on congeners, feedstock, equipment, and professional assessment. No safety conclusion follows from a predicted ABV.

For education and appropriately authorized distillers. US TTB guidance requires prior approval for distilled-spirits production; personal beverage production has no federal exemption. Germany's Alkoholsteuergesetz §32 restricts private alcohol production without the required permissions. These jurisdictional statements were checked on 29 October 2026; verify current federal, state, local, and German customs requirements with the responsible authority before practical operation.