The calculator converts temperature readings to lethal rates, plots the lethal rates against time, and determines F values for a heat process. The area under the curve is determined using the trapezoid rule. Accurate F determinations for most thermal processes can be obtained. In general the more values, the more accurate the value for F will be.
In this section we are going to use simple mathematical techniques, associated with thermobacteriology, to investigate the survival of Mycobacterium avium subsp. paratuberculosis during high temperature short time, HTST, pasteurisation.
Food technologists producing acidic foods such as pickles and sauces often find it difficult to get information on the processing conditions required to obtain commercial sterility. Following experience of working with processors experiencing technical issues including spoilage problems and difficulties in exporting products I have produced a focussed and concise report (Thermal processing of acid fruit and vegetable products. Significant microorganisms, recommended processing time / temperatures, and public health significance of spoilage.) that:
1) Identifies the potential spoilage organisms of acidic foods
2) Discusses the decimal reduction times and Z-values of the major spoilage organisms of acid foods
3) Lists F or P values and reference temperatures for ensuring the production of commercially sterile acid foods
4) Explains how to calculate F values and the number of log reductions of spoilage organisms following processing
5) Explains how to calculate equivalent processes e.g. at higher temperatures using published data
5) Explains the importance of measuring pH over the shelf life of acidified products
6) Provides a summary of the major causes of spoilage of acidic foods and their control
7) Lists literature, including a free On Line database containing around 6000 D-values, concerning the manufacture and control of acid foods.
The booklet can also be used on an IPhone or Android device that can view PDF files.
This report contains 17 pages, 5 tables and 19 references (the table of contents is shown in figure 1). Worked examples are provided and the author is prepared (within reason) to help users having problems providing they are posted on the forum.
The report was updated to version 1.3 on the 30th June 2012 and can be downloaded using the original download URL. The next significant update will be released around December 2012 and will contain more information on the equations underpinning thermal process calculations, more worked examples and Excel spread sheets configured to undertake the calculations. There will also be additional sections including the manufacture of acidic milk products (not covered in this report), validation and quality assurance of heat processes. Donors will be advised of updates which will be available at no cost.
Figure 1. Table of contents of the thermal processing report.
The report is available as an immediate download following a donation of £19.99 (about $32 or 28 Euros) to the Diary Science and Food Technology website. Only make this donation if you understand that you are receiving an educational aid to help you understand the scientific and technological factors influencing the production of commercially sterile acid and acidified foods.
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£19.99 (about $32 or 28 Euros)
Technologists must be able to calculate the cumulate 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."
Options 1 to 3 are available as immediate downloads.
Dry heat sterilisation is widely used for glassware and materials that are not suitable for sterilisation using saturated steam. A range of temperatures and times are used. Currently a temperature of at least 170°C for 30-60 minutes is widely used. The term is not particularly precise since variable concentrations of water may be present.
Dry heat sterilisation is widely used for glassware and materials that are not suitable for sterilisation using saturated steam. A range of temperatures and times are used. Currently a temperature of at least 170°C for 30-60 minutes is widely used. The term is not particularly precise since variable concentrations of water may be present.
The calculator converts temperature readings to lethal rates, plots the lethal rates against time, and determines F values for a heat process whether using saturated steam or dry heat. The area under the curve is determined using the trapezoid rule. Accurate F determinations for most thermal processes can be obtained. In general the more values, the more accurate the value for F will be.
Technologists producing acidic foods such as pickles and sauces often find it difficult to get information on the processing conditions required to obtain commercial sterility. Following experience of working with processors experiencing technical issues including spoilage problems and difficulties in exporting products I have produced a focussed and concise report (Thermal processing of acid fruit and vegetable products. Significant microorganisms, recommended processing time / temperatures, and public health significance of spoilage) that:
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.
Can you destroy Mycobacterium avium subsp. paratuberculosis (MAP) by pasteurization? How important is holding time compared with holding temperature? Use the powerful free tools in this section to answer these questions.
An article on thermal process modelling has been added. This article calculates the effect of HTST treatment on the number of log reductions of major milk pathogens and discusses the temperature milk should be pasteurized if Mycobacterium avium subsp. paratuberculosis (MAP) was designated as a human pathogen. The log reductions refer to log10 or decimal (10 fold) reductions in the concentration of viable bacteria.
Effect of HTST treatment on the number of log reductions of major milk pathogens.
DSFT provides a range of thermal processing consultancy services to food and pharmaceutical manufacturers. These include:
There will be occasions when a food manufacturer wishes to use a different, but equivalent lethal thermal process. How does the processor calculate the equivalent process?
This article explains how to calculate an equivalent thermal or heat process at a higher or lower temperature and provides access to a free On Line calculator for checking your calculations.
Many students have problems in understanding the mathematics describing the destruction of microorganisms by heat. Log reductions of pathogens and equivalent time-temperature treatments along with the associated lethalities account for a large part of the harder to understand topics. The quiz below is a simple test of of some of the basic concepts. Note Z value is not dealt with in this quiz. If there is sufficient interest I will provide the answers.
This article investigates how to calculate the lethal effects of UHT treatment and the usefulness of TTIs for differentiating sterilised, direct and indirectly processed UHT-treated milk. The importance of accessing accurate temperature time-data and knowing holding tube dimensions, flow rate, average and minimum holding time and the flow characteristics (Reynolds number) are discussed. The reliability of a model developed by Claeys et al. (2003) to predict the effects of UHT-processing on hydroxymethylfurfural, lactulose and furosine concentrations in milk is discussed. Free On Line calculators for calculating holding time, average flow rate, holding tube length in UHT and HTST plants are provided. A free On Line calculator programmed using the thermal constants calculated by Claeys et al. (2003) is provided to calculate hydroxymethylfurfural, lactulose and furosine concentrations following heat treatment in skim, semi fat and full fat milks. This calculator also calculates F0, B*, C* and % destruction of thiamine. Two methods of numerical integration are used to measure the cumulative lethal and chemical effects of UHT treatment, namely the Trapezoid and Simpson's rules.
Typical UHT treatments involve heating milk to 137℃ to 150℃ in a continuous-flow process and holding at that temperature for one or more seconds before cooling rapidly to room temperature. The milk is then aseptically packaged to give a product that is stable for several months at ambient temperature.
In Europe, UHT treatment is defined as heating milk in a continuous flow of heat at a high temperature for a short time (not less than 135 °C in combination with a suitable holding time, not less than a second) such that there are no viable microorganisms or spores capable of growing in the treated product when kept in an aseptic closed container at ambient temperature (Reg EC 2074/2005).
This section provides the context to using Excel to calculate the cumulative lethal effects (at all stages during processing) of heat on microorganisms and provides an explanation of how the Excel spreadsheets and On Line calculators available for download from the Dairy Science and Food Technology (DSFT) work.
Here we provide an overview of the background, including a summary of the underlying mathematics, required to produce an Excel spreadsheet for performing basic thermal processing calculations. Note I am not providing a guide to using spreadsheets but basic information that a competent Excel user should be able to use to make their own thermal processing spreadsheet.
DSFT has an extensive range of free-On Line resources for undertaking a wide range of thermal process calculations. This page provides access to a range of Microsoft Excel spreadsheets that can be downloaded for a small donation and will work on a PC or Mac without access to the Internet. In general these spreadsheets are similar to their corresponding free applications on this website.
A number of the spreadsheets have lite or demonstration versions for evaluation prior to purchase. If you want to test a version that does not offer a test version contact me and I can arrange to provide this.
These donations are important. They contribute towards the running costs of the website and enable me to provide free access to the website rather than require a subscription.
As previously discussed (Mullan, 2016), there will be occasions when a food manufacturer who has been using two different but equivalent thermal processes from a lethality perspective wishes to use a different, but equivalent lethal thermal process. This is straightforward if the z-value is known (Mullan, 2016). How does the processor calculate the equivalent lethal process if z is unknown?
This article explains how to calculate z using the time and temperature values of the two different, but equivalent lethal processes, and provides access to a free On Line calculator for checking your calculations.
This article provides access to a calculator and an introduction to the mathematics derived by Dr Tomas Skoglund that enables the z-value, a term used in microbial thermal death time calculations, to be corrected to comply with Arrhenius calculations. This value can be defined in several ways, including that z is the number of degrees that the temperature must be increased to achieve a tenfold (i.e.,1 log10) reduction in the decimal reduction value (D-value). The D-value is the time required to reduce the number of organisms by 1 log cycle and is an indication of the heat resistance of an organism.
There are two main approaches to calculating the bactericidal effectiveness of a heat process namely the Bigelow and Arrhenius methods. Both methods require the use of constants to allow for the temperature dependence of the kinetics of thermal destruction. The Bigelow method uses z-value (SI unit K or °C) and the Arrhenius model uses activation energy (Ea, SI unit J/ mol).
Dry heat sterilisation is widely used for glassware and materials that are not suitable for sterilisation using saturated steam. A range of temperatures and times are used. Currently a temperature of at least 170°C for 30-60 minutes is widely used. The term is not particularly precise since variable concentrations of water may be present in the oven used (Sandle, 2013).