Technologists must be able to calculate the cumulative lethality of a heat process normally referred to as F. This is done by defining a reference temperature, e.g. 121.1 °C for a F0 calculation using a low acid food or e.g. 93.3 °C for an acid product, at which the equivalent lethal effects experienced during heating and cooling at lower temperatures are calculated.
The area under the lethality curve is normally calculated using numerical integration. The most commonly used method is the trapezium or trapezoid method. An alternative, more accurate, but slightly more complicated method, is to use Simpson's rule or to be more correct Simpson's rules.
Site users can choose to download:
1) an Excel spreadsheet based-lethal rate calculator programmed using the trapezoid rule;
2) a more accurate and easier to use Excel workbook using both of Simpson's rules and also offering the option of using the trapezoid rule. This download also contains a spreadsheet to convert Z-values in Fahrenheit or Celsius to the desired measurement system and a PDF document listing D, F, Z values and reference temperatures for the major spoilage organisms of significance to processing low acid and acid foods. A link to a free On Line resource that details thermal resistance data for many spoilage and pathogenic organisms significant to the food and pharmaceutical industries is also provided;
3) all the spreadsheets above and the author's Ebook "Thermal processing of acid fruit and vegetable products. Significant microorganisms, recommended processing time / temperatures, and public health significance of spoilage."