Canning and Fish Packaging Technology

4.6.2.Thermal Death Time (TDT) curve on a semilog paper

Unit 4 - Thermal process for canned foods

4.6.2.Thermal destruction/ thermal death time (TDT) curve on a semilog paper

The slope of a TDT curve is indicative of the thermal tolerance of a bacteria. The steeper a TDT curve is, the faster the destruction of the bacteria indicating lower tolerance. Thermal tolerance can be compared by Z values. Z value is the number of degrees (°F or °C) required for the TDT curve to pass through one log cycle. The effect of temperature on destruction of cells decreases as the Z value increases. Instead of TDT, if D values are plotted on the log scale against temperature on the linear scale as in thermal destruction curve, a straight line curve parallel to TDT curve is obtained. This curve is known as Phantom TDT curve and has the same slope as TDT curve.