Engineering explained / BREW

The beer makes heat.
The jacket makes the recipe.

Inside the tank, yeast are making alcohol, carbon dioxide and heat. Grow the tank and the cooling surface struggles to keep up. Move the size slider and see why.

The agent layer behind the engineering

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Explore the energy balance ↓

01 / The scale-up trap

100× the beer.
Only 21.5× the wall.

A larger tank has more cooling area, but less area for each litre of beer. This comparison keeps the shape and jacket coverage the same.

10 to 1,000 hectolitres. 1 hL = 100 litres.

An illustrative multiplier on U × jacket coverage × temperature difference.

Reference 10-hectolitre fermentation tank10 hL
Larger fermentation tank shown at its relative linear size1,000 hL
100×volume
21.5×surface area
21.5%wall per litre, relative to 10 hL

Conceptual generated cutaway. Glycol stays in the outer jacket, separate from the beer. Relative linear size is accurate; equipment details are illustrative.

V ∝ L³   A ∝ L²   A/V ∝ V−1/3

At 1,000 hL, each litre has 4.64× less cooling wall than at 10 hL.

02 / The energy balance

Heat in. Heat out.
The difference stays in the beer.

m cp dT/dt = Q̇yeast − U Ajacket (T − Tglycol) + Q̇ambient

The jacket carries fermentation heat into a circulating glycol loop. The chiller rejects that heat to the surroundings. Around −3 °C can be a glycol supply temperature; it is not the beer temperature and the circulating mixture remains liquid.

Illustrative peak day, using the sliders above

Fermentation heat and jacket capacity over a batchA normalized fermentation heat curve peaks in the middle of the batch. A horizontal line shows available cooling at the target beer temperature.StartEndYeast heatCooling at setpoint
100.0 kWpeak fermentation heat
21.5 kWjacket cooling at setpoint
+0.71 °C/hinitial peak temperature trend

The jacket cannot remove the peak fermentation heat at the target temperature.

Show the model assumptions

The reference 10 hL tank generates 1 kW at peak and removes 1 kW at the target temperature. This is a chosen example, not a recommended design duty. Heat generation scales with volume; cooling at setpoint scales with area and the selected improvement. Density = 1 kg/L, cp = 4 kJ/(kg·K), ambient heat ignored. The displayed temperature trend is the instantaneous derivative at setpoint, not a predicted final temperature. As beer warms, the temperature difference and cooling change. The time curve illustrates a peak, not measured yeast kinetics. Real sizing also includes batch schedules, crash cooling, heat leaks, jacket coverage, flow and equipment performance.

Why “about ten degrees” is an estimate

With 8 kg of fermented sugar per hL, a heat release of 500 kJ/kg and 100 kg of liquid with cp ≈ 4 kJ/(kg·K), no cooling gives ΔT ≈ 10 °C. Choosing 400–600 kJ/kg as a sensitivity range changes that to 8–12 °C. These are illustrative assumptions, not a universal fermentation rise.

ΔTadiabatic = (8 kg × 500 kJ/kg) / (100 kg × 4 kJ/(kg·K)) = 10 K

03 / Temperature is part of the recipe

A few degrees can change the flavour.

Yeast choice and temperature both matter. The BJCP guide gives typical ale and lager temperature bands, with exceptions by strain.

Ale: 13–24 °CLager: 8–13 °C

The guide reports that a fourfold increase in ester production can occur between 16 and 20 °C. This example is not a universal law, and changing temperature alone does not turn ale yeast into lager yeast.

Illustrative relative ester production reported by BJCP. Strain, wort and fermentation conditions also affect the result.

04 / The other product

The gas adds up.

Generated educational illustration of a budding yeast cell, incoming sugar and outgoing products
Conceptual yeast illustration. Fermentation produces ethanol and carbon dioxide while releasing heat.

Using about 4 kg of CO₂ generated per hL, the selected tank produces:

4,000 kgfrom 100,000 litres of beer

That is total batch production, not the gas flow rate at every moment. Alcohol strength and attenuation change the actual amount.

CO₂ is colourless and can accumulate in poorly ventilated low spaces. Gas monitoring and properly designed venting matter. This calculator is not a ventilation design tool.

Recovered fermentation CO₂ can be cleaned, compressed and reused. Atlas Copco gives an example of 3 kg used per hectolitre, not per tank; that plant-use figure is not a target dissolved carbonation concentration.

Sources & scope

Follow the numbers.

  1. BJCP: Yeast and Fermentation. Typical temperature ranges and the possible fourfold ester example.
  2. G&D Chillers: brewery glycol sizing. Supply temperatures, peak loads and simultaneous cooling duties.
  3. Atlas Copco: brewery CO₂ recovery. Approximate gas generation and brewery demand per hectolitre.
  4. Brewers Association: venting and management of CO₂. Exposure depends on the actual brewery and needs measurement.
  5. Standard thermodynamic quantities. Glucose → 2 ethanol + 2 CO₂ gives about −69 kJ/mol using the stated standard formation values, roughly 380 kJ/kg glucose. Actual fermentation heat and extract composition vary. The 500 kJ/kg used above is an illustrative input.
  6. Scale ratios follow directly from geometric similarity. 1002/3 = 21.54; 1001/3 = 4.64. The interactive energy model is a teaching example, not equipment selection or a fermentation kinetics model.

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