Cooling Curve & Half-Cool the Field Heat Out

Half-cooling time (often written Z) is the time it takes to remove half the temperature difference between the produce and the coolant. Because cooling follows Newton's law of cooling — an exponential approach to the coolant temperature — each half-cooling period removes half of the remaining gap. It is calculated as Z = ln(2) ÷ C, where C is the cooling coefficient (per hour) for the method and commodity.

Seven-eighths cooling is when 7/8 (87.5%) of the original temperature difference has been removed — the produce is then considered commercially cool. It equals exactly three half-cooling times: 7/8 time = ln(8) ÷ C = 3 × Z. Most precooling targets the 7/8 point because chasing the last eighth takes as long again as the first seven-eighths and is rarely worth the extra time in the cooler.

Typically four to ten times faster. Room cooling relies on cold air drifting past packages and has a low cooling coefficient (around 0.10 per hour, so a half-cooling time near 7 hours). Forced-air cooling pulls cold air through vented packages and reaches a coefficient near 0.40 per hour — a half-cooling time under two hours. For high-respiration crops that difference is the difference between sale-ready and spoiled.

Vacuum cooling is the fastest for leafy, high-surface-area crops, with a cooling coefficient around 1.8 per hour (half-cooling under 25 minutes). Hydrocooling is next for water-tolerant produce, then package or liquid ice, then forced-air, with room cooling slowest. The right choice balances speed against what the commodity tolerates — vacuum suits lettuce, hydro suits sweet corn, but neither suits a dry-surface fruit like a strawberry, which needs forced-air.

Cooling is driven by the temperature gap between the produce and the cooling medium. As the produce approaches the coolant temperature the gap shrinks toward zero and cooling slows to a crawl — mathematically it never quite reaches the coolant temperature. So if your target pulp temperature is at or below the coolant temperature, it is unreachable; you must lower the coolant (colder air or water) to hit it.

Field heat is the pulp temperature of the produce as it arrives — measure it with a probe thermometer pushed into the centre of a representative item. Coolant temperature is the temperature of the medium doing the cooling: cold-room air, hydrocooler water, or the vacuum chamber set-point. The bigger the gap between them, the faster the early cooling, but the half-cooling and 7/8 times depend only on the method's cooling coefficient.

Yes. Respiration roughly doubles for every 10°C rise, so warm produce ages fast and consumes its own reserves. Pulling field heat out quickly slows respiration and the growth of decay organisms, so the produce reaches the consumer with more shelf life left. The tool estimates the relative shelf-life gain versus slow room cooling — for fast-respiring crops cooled promptly, it is substantial.

The cooling coefficient C (per hour) is how fast a given method-and-commodity combination sheds heat — the rate constant in Y(t) = exp(−C·t), where Y is the unaccomplished cooling (the fraction of the original gap still remaining). A higher C means faster cooling and a shorter half-cooling time. Real values vary with air or water velocity, package venting and product size, so treat the table figures as planning values.

No. Each commodity has a recommended storage pulp temperature, and chilling-sensitive crops must not be cooled below a safe floor. Most temperate fruits and many vegetables target around 0°C, but tomatoes, cucumbers, peppers, mangoes and bananas chill-injure below roughly 7–13°C and so target a warmer pulp temperature. The tool uses each commodity's recommended target from the reference table.

From the exponential cooling law: t = −ln((target − coolant) ÷ (field − coolant)) ÷ C. In words, it finds how many cooling time-constants are needed to shrink the temperature gap from its starting value down to the residual gap at the target temperature. If the target sits at or below the coolant temperature, the time is effectively infinite and the tool flags the target as unreachable.

Yes — that is the point of the curve. Switch the precooling method while keeping the commodity, field heat and coolant fixed, and the cooling curve visibly steepens or flattens as the half-cooling and 7/8 points move. That lets you weigh, for example, whether the speed of hydrocooling justifies its handling over forced-air for your crop.

No. The calculation runs entirely in your browser using the exponential cooling model and the built-in method and commodity tables. Nothing you enter is sent anywhere.