Hot-Water Treatment & Kill the Pest, Spare the Fruit
Disinfests mango
Pick the fruit and quarantine pest, enter the bath and starting pulp temperatures, and read the centre temperature and hold time for probit-9 mortality, the heat-up time, the total immersion and the margin below the heat-damage ceiling — so you kill the eggs without cooking the fruit.
Hot-water treatment
Next: run it. Hold the bath at 47°C and leave the fruit in for the full 2 h 20 min (1 h 20 min for the centre to reach 46°C, then 60 min hold). Probe the coldest, biggest fruit's centre to confirm it holds 46°C, and hydrocool straight after to stop heat injury.
Centre heating follows Newton's law: Tc(t)=Tbath−(Tbath−T0)·e^(−k·t). Time to lethal = −ln((Tbath−Tlethal)/(Tbath−T0))/k. A quarantine treatment must hold the COLDEST point (centre/seed) at the lethal temperature for the full schedule to reach probit-9 (≈99.997%) mortality, without the surface exceeding the damage ceiling. Sources: USDA-APHIS PPQ Treatment Manual Schedule T102 (mango 46.1°C/65–90 min); postharvest HWT literature (Jacobi, Armstrong, Sharp). Always treat to the official schedule for your origin/pest.
Hot-water treatment — key facts
- Centre heating
- Tc(t) = Tbath − (Tbath − T0)·e^(−k·t)
- Heat-up time
- t = −ln((Tbath−Tlethal)/(Tbath−T0)) ÷ k
- Total immersion
- heat-up time + required hold
- Mango fruit fly (T102)
- centre 46.1°C, 65–90 min by size
- Mango damage ceiling
- ≈ 48°C
- Quarantine standard
- probit-9 (99.9968% mortality)
- Fails if
- bath ≤ lethal temp, or bath > ceiling
- Privacy
- Runs in your browser; nothing uploaded
Fruit heat-damage ceilings and heating rates
The fruit sets the heat-damage ceiling (how hot the bath can go) and how fast its centre heats. Larger, denser fruit heat slower (lower k), so they need longer immersion. These reference values drive the heating curve.
| Fruit | Damage ceiling (°C) | Centre heating k (1/min) | Typical pulp (°C) | Notes |
|---|---|---|---|---|
| Mango (≤375 g) | 48.0 | 0.060 (moderate) | 25 | APHIS T102: centre 46.1°C / 65 min for fruit ≤375 g. |
| Mango (376–570 g) | 48.0 | 0.045 (slow) | 25 | APHIS T102: centre 46.1°C / 75 min for 376–570 g. |
| Mango (571–700 g) | 48.0 | 0.038 (slow) | 25 | APHIS T102: centre 46.1°C / 90 min for 571–700 g; thicker fruit heats slowest. |
| Papaya | 49.0 | 0.055 (moderate) | 26 | Two-stage HWT in practice; flesh tolerates ~49°C briefly. |
| Citrus (orange) | 46.0 | 0.050 (moderate) | 22 | Rind is heat-sensitive; lower ceiling, watch for pitting. |
| Carambola (starfruit) | 47.0 | 0.080 (fast) | 24 | Thin ribs heat fast; short schedules. |
| Guava | 47.5 | 0.060 (moderate) | 25 | Hot-water disinfestation used for fruit-fly markets. |
| Lychee | 47.0 | 0.090 (fast) | 25 | Small, heats very fast; brief immersion. |
Quarantine pest schedules
| Pest | Lethal centre (°C) | Required hold (min) | Notes |
|---|---|---|---|
| Fruit fly (Anastrepha/Bactrocera/Ceratitis) | 46.1 | 60 | APHIS T102 baseline: pulp 46.1°C; hold scales 65–90 min with fruit size. |
| Mango seed weevil | 46.1 | 90 | Deeper-seated pest in the stone; longer hold to heat the seed through. |
Sources: USDA-APHIS PPQ Treatment Manual, Schedule T102 (hot-water immersion for fruit flies in mango); postharvest hot-water disinfestation literature (Jacobi, Armstrong; Sharp & McGuire). Heating coefficients are representative planning values. Always treat to the official APHIS (or your national plant-protection organisation's) schedule for your specific fruit, origin and pest under accredited supervision.
Reach the lethal temperature without scalding the fruit
A quarantine hot-water treatment must hold the coldest point of the fruit — the seed or pulp centre — at the lethal temperature for the full schedule so the pest reaches probit-9 mortality. But the fruit is immersed at the bath temperature, and the centre lags: it heats toward the bath on an exponential curve set by the fruit's size and a heating coefficient. The operator has to run the bath long enough that the centre reaches the target and then holds it, all while keeping the bath below the temperature that cooks the fruit.
This tool plots that heating curve for your fruit, pest, bath temperature and starting pulp temperature. It marks the moment the centre crosses the lethal line, the end of the hold, and draws the heat-damage ceiling as a do-not-exceed line. If the bath is below the lethal temperature the centre can never reach it; if the bath is above the ceiling it scalds the fruit — so the workable window can be tight, and the tool shows you exactly where you stand.
How to use it in five steps
- 1Pick the fruit
Select your fruit and size class — the tool sets its heat-damage ceiling and how fast the centre heats.
- 2Choose the pest
Fruit fly or mango seed weevil — each carries its lethal centre temperature and required hold time.
- 3Enter the temperatures
Enter the hot-water bath temperature and the starting pulp temperature measured at the fruit centre.
- 4Read the schedule
Read the centre heat-up time, the total immersion time and the margin below the damage ceiling.
- 5Confirm and treat
Check for a pass, adjust the bath if it is tight or fails, then run the official schedule and cool the fruit.
Frequently Asked Questions
What is hot-water disinfestation?+
Hot-water disinfestation (hot-water treatment, HWT) is a quarantine postharvest treatment that immerses fruit in a heated bath long enough to kill the eggs and larvae of quarantine pests — chiefly fruit flies and the mango seed weevil — so the fruit can be exported without spreading the pest. The treatment is defined by the temperature the coldest point of the fruit must reach and how long it must stay there, and it must do that without heat-damaging the fruit.
What hot-water time and temperature kills fruit-fly eggs without cooking the fruit?+
The APHIS T102 baseline for fruit flies in mango holds the fruit centre at 46.1°C, with the hold scaling from 65 minutes for fruit ≤375 g up to 90 minutes for 571–700 g fruit. Mango heat-damages above roughly 48°C, so the bath is run a little above 46.1°C but kept below the damage ceiling. Enter your fruit, bath temperature and starting pulp temperature and the tool returns the centre heat-up time, the total immersion, and how much margin you have below the damage ceiling.
What is probit-9 mortality?+
Probit-9 is the quarantine security standard: a treatment that kills 99.9968% of the target pest, equivalent to no more than about 32 survivors per million treated. Quarantine hot-water schedules are validated to reach probit-9 at the stated centre temperature and hold time, which is why the centre — the coldest, slowest-heating point of the fruit — must reach and hold the lethal temperature, not just the surface.
Will a 46.7°C bath cook my mango?+
Not on its own — mango heat-damages above about 48°C, so a 46.7°C bath sits roughly 1.3°C below the ceiling and is the normal operating range for T102. The risk is overshoot: if the bath drifts up or the fruit sits in a hot spot, the surface can scald. The tool shows the ceiling margin and flags a 'tight' verdict when the bath is within 0.5°C of the damage ceiling so you tighten temperature control before running it.
Why does the fruit centre lag behind the bath temperature?+
Heat has to conduct from the bath through the flesh to the centre, so the centre warms on an exponential (lumped-capacitance) curve, approaching the bath temperature but never quite reaching it. Bigger, denser fruit heat slower — which is why a large mango needs a longer immersion than a small one even though the lethal centre temperature is the same. The tool models this with a per-fruit heating coefficient k.
How is the heat-up time calculated?+
The centre temperature follows Newton's heating law Tc(t) = Tbath − (Tbath − T0)·e^(−k·t), where T0 is the starting pulp temperature and k is the fruit's heating coefficient. Solving for the time to reach the lethal temperature gives t = −ln((Tbath − Tlethal)/(Tbath − T0)) / k. The total immersion is that heat-up time plus the required hold, so the centre both reaches and holds the lethal temperature.
What happens if the bath is below the lethal temperature?+
The centre can only ever approach the bath temperature, so a bath at or below the lethal target can never bring the centre up to it — the treatment can never reach probit-9 no matter how long you run it. The tool flags this as a 'centre never reaches lethal temp' failure and tells you to raise the bath above the lethal temperature (and below the damage ceiling) before re-checking.
Why does a larger mango need a longer treatment?+
A larger mango has more flesh between the surface and the centre, so its heating coefficient k is smaller and the centre warms more slowly. At the same bath temperature, the centre of a 571–700 g mango takes noticeably longer to reach 46.1°C than a ≤375 g fruit — which is exactly why APHIS T102 lengthens the hold from 65 to 90 minutes as the fruit gets bigger. The tool uses a representative k for each size class.
What is the heat-damage ceiling?+
The heat-damage ceiling is the bath/whole-fruit temperature above which the fruit scalds, pits or develops internal injury. It varies by commodity — about 48°C for mango, 49°C for papaya, but only 46°C for heat-sensitive citrus rind. The bath must sit below this ceiling while still being above the lethal centre temperature, so the workable window can be narrow; the tool shows the margin and warns when it is too tight.
Should I cool the fruit after treatment?+
Yes. After the hold is complete, hydrocool or air-cool the fruit promptly to stop residual heat from continuing to injure it and to bring it into the cold chain. Leaving treated fruit warm lets the surface keep cooking and accelerates ripening and decay, undoing the benefit of a carefully run treatment.
Does this replace the official quarantine schedule?+
No. This is a planning and training tool. The legally valid treatment is the official APHIS (or your national plant-protection organisation's) schedule for the specific fruit, origin and pest, run under accredited supervision with calibrated probes. Use the calculator to understand the heat-up and hold dynamics and to sanity-check temperatures, then treat to the approved schedule.
Can hot-water treatment handle the mango seed weevil?+
The mango seed weevil sits deep in the stone, so it heats more slowly than fruit-fly eggs in the flesh and needs a longer hold — the schedule in the tool extends the hold to 90 minutes to drive heat through to the seed. Because the centre must heat further in, the total immersion is longer, and the margin against the damage ceiling matters even more.
What bath and pulp temperatures should I enter?+
Enter the actual bath set-point you can hold (the T102 baseline is 46.1°C; operators often run 46.7°C to keep the centre above target) and the starting pulp temperature of the fruit as it enters the bath, measured with a probe in the centre of a representative fruit. Warmer incoming fruit reaches the lethal centre temperature faster; cold fruit straight from storage takes longer to heat up.
Is anything uploaded?+
No. The calculation runs entirely in your browser using the lumped-capacitance heating model and the built-in fruit and schedule tables. Nothing you enter is sent anywhere.