Calculate pasteurization units (PU) for beer from hold time and temperature, or find the time or temperature needed to reach a target PU value.

Temperature at the product’s coldest point, assumed constant for the whole hold time.

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Pasteurisation Units Formula

PU = t × 1.393(T - 60)

Formula source:  Enevoldsen B.S. “Determining Pasteurization Units from Residual Melibiase Activity in Lager Beer.” J. Amer. Soc. Brewing Chemists 43 (4), 1985

Variables:

  • PU is the Pasteurisation Units (units)
  • t is the time (minutes)
  • T is the temperature (°C)

For the original beer model at a constant product temperature, multiply time in minutes by 1.393 raised to (temperature in °C minus 60). This factor corresponds to z = ln(10)/ln(1.393) ≈ 6.946°C, not exactly 7°C. The separate z-value model uses PU = t × 10^((T − Tref)/z). One reference minute at 60°C is one PU; a custom reference changes the equivalent-minute convention. Integrate the lethal-rate factor over time for a varying temperature history.

How to Calculate Pasteurisation Units?

The following steps outline how to calculate the Pasteurisation Units.

  • First, determine the time (minutes). 
  • Next, determine the temperature (°C). 
  • Next, gather the formula from above = PU = t *1.393^(T-60).
  • Finally, calculate the Pasteurisation Units.
  • After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

time (minutes) = 2

temperature (°C) = 60

FAQs on Pasteurisation Units

What are Pasteurisation Units?

Pasteurisation units express an equivalent heat exposure under specified reference-temperature and thermal-sensitivity assumptions. They can help compare a validated beverage process, but a calculated PU value alone does not establish pathogen reduction, product safety or regulatory compliance. Use product-specific validated thermal parameters, targets and coldest-point product-temperature measurements.

Why is 60 subtracted from the temperature in the formula?

The original beer convention uses 60°C as its reference: one minute at that temperature gives one PU. Temperatures above and below the reference change the modeled rate. This reference and the selected z-value are model parameters, not universal values for all foods.

Can the Pasteurisation Units formula be used for any type of food or beverage?

While the Pasteurisation Units formula provides a general guideline for assessing the effectiveness of pasteurisation, different foods and beverages may require specific considerations based on their composition, pH, and other factors. It is important to consult relevant food safety guidelines and regulations for specific products.

How does time affect the calculation of Pasteurisation Units?

Time is a critical factor in the calculation of Pasteurisation Units because it determines the duration of exposure to a specific temperature. Longer exposure times at a given temperature will result in higher Pasteurisation Units, indicating a more effective pasteurisation process. This relationship allows for adjustments in processing times and temperatures to achieve the desired level of pathogen reduction.