Determine the thermal lethality and required pasteurization time for food safety.
Calculated Required Time
What is the NASA TT (Time-Temperature) Calculation?
The NASA Time-Temperature (TT) concept originates from the Hazard Analysis Critical Control Point (HACCP) systems developed for space flight. It is used to calculate the necessary time required to achieve a specific microbial reduction (typically a 6.5-log or 7-log reduction in Salmonella) at temperatures lower than the standard "instant-kill" temperature of 165°F (74°C).
The Mathematics of Thermal Lethality
Microbial destruction is not instantaneous but follows a logarithmic decay. The formula used in this calculator is based on the thermal death time (TDT) principle:
t = t_ref * 10^((T_ref – T) / Z)
t: The required time at your current temperature.
t_ref: The known time required at a reference temperature.
T_ref: The reference temperature used for the standard.
T: Your actual cooking temperature.
Z: The Z-value, representing the temperature change required to move the D-value by a factor of 10.
Realistic Example:
If the safety standard requires 14 seconds at 160°F (Reference), but you are cooking chicken at 145°F (Target) with a Z-value of 12.5°F: Required Time = 14 * 10^((160 – 145) / 12.5) = 14 * 10^(1.2) ≈ 222 seconds (3.7 minutes).
Why Temperature Precision Matters
In aerospace food systems and modern sous-vide cooking, maintaining a specific temperature over a longer duration allows for the same level of pasteurization as high-heat cooking while preserving the texture and moisture of the food. This calculator helps food scientists and professional chefs ensure they meet USDA/NASA safety benchmarks.
function calculateNASA() {
var T = parseFloat(document.getElementById('targetTemp').value);
var Tref = parseFloat(document.getElementById('refTemp').value);
var tRef = parseFloat(document.getElementById('refTime').value);
var z = parseFloat(document.getElementById('zValue').value);
var resultDiv = document.getElementById('nasaResult');
var timeOutput = document.getElementById('timeOutput');
var logicNote = document.getElementById('logicNote');
if (isNaN(T) || isNaN(Tref) || isNaN(tRef) || isNaN(z) || z <= 0) {
alert("Please enter valid numerical values. Z-value must be greater than zero.");
return;
}
// Formula: t = t_ref * 10^((T_ref – T) / Z)
var exponent = (Tref – T) / z;
var requiredTimeSeconds = tRef * Math.pow(10, exponent);
resultDiv.style.display = "block";
if (requiredTimeSeconds < 1) {
timeOutput.innerHTML = requiredTimeSeconds.toFixed(3) + " Seconds";
logicNote.innerHTML = "At this temperature, pasteurization is nearly instantaneous.";
} else if (requiredTimeSeconds < 60) {
timeOutput.innerHTML = requiredTimeSeconds.toFixed(1) + " Seconds";
logicNote.innerHTML = "Maintain this internal temperature for the duration shown above for food safety.";
} else if (requiredTimeSeconds < 3600) {
var mins = Math.floor(requiredTimeSeconds / 60);
var secs = Math.round(requiredTimeSeconds % 60);
timeOutput.innerHTML = mins + " Minutes " + secs + " Seconds";
logicNote.innerHTML = "Ensure internal temperature remains stable to achieve lethality.";
} else {
var hrs = (requiredTimeSeconds / 3600).toFixed(2);
timeOutput.innerHTML = hrs + " Hours";
logicNote.innerHTML = "Warning: Extended dwell time required. Ensure precise temperature control.";
}
}