The Wort Chiller Cooling Time Estimator predicts how long it will take to bring boiling wort down to pitching temperature with your chiller. Knowing this lets you time the rest of brew day — sanitising the fermenter, preparing yeast — so nothing waits on a kettle that is still too hot.
How it works
Cooling follows Newton’s law of cooling: the rate of temperature drop is proportional to the difference between the wort and the coolant. Mathematically:
T(t) = Tw + (T0 − Tw) × e^(−k·t)where T0 is the starting wort temperature, Tw is the incoming groundwater
temperature, t is time in minutes, and k is a rate constant that depends on
the chiller type and the wort volume.
Solving for the time to reach a target temperature Tt:
t = −(1 / k) × ln( (Tt − Tw) / (T0 − Tw) )Larger volumes lower the effective k (more thermal mass per unit of cooling
surface), so the constant is scaled by volume. Immersion chillers use a smaller
base constant than counterflow or plate chillers, which cool a thin stream of
wort with a much larger temperature gradient.
Temperature limits
A chiller can never cool wort below the temperature of the water running through it. If your target is at or below the groundwater temperature, the estimator reports that the target is unreachable with that coolant and you would need an ice bath, pre-chiller, or glycol loop.
Chiller types compared
Understanding why each chiller type has a different rate constant helps you interpret the estimate and choose the right equipment.
Immersion coil — a coiled copper or stainless tube dropped into the hot kettle. Groundwater flows through the coil while the wort sits still (or is stirred manually). Heat transfer is limited by the coil surface area and by the natural convection of wort around it. Effective but slow, especially for large batches or warm groundwater. Stirring the wort with a mash paddle significantly speeds the process by continuously bringing hot wort into contact with the coil.
Counterflow chiller — wort and cold water flow in opposite directions through two concentric tubes. As hot wort enters one end, it immediately encounters the coldest water; by the time the wort exits, it has given up most of its heat. The continuously replenished cold stream creates a large temperature gradient throughout, making counterflow chillers far faster per volume than immersion coils.
Plate chiller — thin stainless plates are stacked and alternated between wort and cold water channels. The enormous combined surface area across many plates makes plate chillers the fastest commonly available option, often chilling wort to pitching temperature in just a few minutes. They require clean, well-filtered wort to avoid clogging.
Worked example
For a 23 L (roughly 6 US gallon) batch of 100°C wort targeting 20°C with 15°C groundwater:
- Immersion coil: typically around 20–30 minutes with occasional stirring.
- Counterflow: often 10–15 minutes at moderate flow rates.
- Plate chiller: can reach pitching temperature in as little as 5–8 minutes when flow rates are matched.
These are planning estimates. The figure is a planning estimate — stirring the wort, increasing water flow, and using a pre-chiller all shorten the real time. Groundwater temperature also varies significantly by season and region; summer groundwater in warm climates can be 5–10°C warmer than winter, adding meaningful minutes to an immersion chill.
Practical tips for brew day
- Plan backwards. Note the estimated chill time, then start chilling as soon as flameout so you know when the fermenter needs to be ready.
- Pre-chill your water line. Run cold water through the chiller for a minute before connecting to the kettle so the first wort does not heat the tubing.
- For lager pitching temperatures (around 10–12°C), groundwater alone is often insufficient in warmer months. An ice-bath pre-chiller or glycol chiller extends the reach below groundwater temperature.