It can be difficult for entrepreneurs to obtain starter cultures for trials. This article provides contact details of some culture suppliers.

The isolation of lactic acid bacteria from raw and pasteurized milk is discussed.

Mr George DoranGeorge Doran graduated with a 2:1 honours degree in Food Technology from the College of Agriculture and Food Technology in Northern Ireland in 2015. Mr Doran's final year research project was entitled "An Investigation of Biofouling in Two Mozzarella Cheese Manufacturing Plants".  

 George completed his food technology internship at Cottage Catering, Dromore, N. Ireland and gained experience in Quality Assurance, New Product Development and Production.

George has achieved several academic distinctions and has extensive work experience gained through part-time work in the security and retail sectors.

Included amongst George's achievements are:

  • Member of the winning team for the Chesapeake Product Development Challenge in December 2013
  • Represented IFST Ecothrophelia in London at Food Matters Live in November 2014



Refrigerated storage of raw milk is used to limit the growth of microorganisms in milk prior to processing. It has been known for some time that the quality and yield of cheese produced from bulk cooled milk may be adversely affected by this procedure (Weatherup et al., 1988; Weatherup and Mullan, 1993). The reduced yield and poor quality may be due to physico-chemical changes in the state of several milk components e.g. dissociation of micellar casein, mainly Κ-casein into a soluble phase, occurs during the first 48 h of storage at 4° and 7° C. This results in losses of fat and curd fines, weaker curd, more moist curd and a slightly lower yield. Partial reversal of dissociation occurs after further storage. The reduced yield and quality can also be due to the activity of proteases and lipases produced by psychrotrophic bacteria.

Despite the work that has been done over many years milk is still being stored for extended periods (1-3+ days on some farms) and cheesemakers are again (2019) reporting problems with the yield and quality of cheese produced using this milk.

Following several queries related to milk quality and cheese manufacture I am providing a report written by Wilf Weatherup and me some years ago that may be helpful.

A simple calculator has been provided using the total viable count of milk prior to pasteurisation and a regression equation to predict the grade value of Cheddar cheese.

Ice cream processors are required to meet or exceed the pasteurisation time temperatures specified in their jurisdiction. Details of minimum requirements are given in Table 1.

Table 1. Minimum temperature-time criteria for pasteurising ice cream mixes in selected countries


Heat treatment*

Regulation/Statutory Instrument and reference



69°C for 30 minutes

80°C for 25 seconds

Code of Good Practice for High-Temperature Short-Time Pasteurizers (HTSTs). (Anon, 1991)

New Zealand

**69°C for 20 minutes

**74°C for 10 minutes

**79.5°C for 15 seconds

**85.5°C for 10 seconds

DPC 3: Animal Products (Dairy): Approved Criteria for the Manufacturing of Dairy Material and Product. (DPC 3, 2010)


65.6°C for 30 minutes
71.1°C for 10 minutes
79.4°C  for 15 seconds 148.8°C for two seconds

The Dairy Products (Hygiene) Regulations 1995. (Anon, 1995)


69°C for 30 minutes

80°C for 25 seconds

83°C for 15 seconds

Grade A Pasteurized Milk Ordinance- 2019 Revision. (PMO, 2019)

*Holding times and temperatures are minimum values. Holding time refers to the minimum residence time of the fastest traveling particle. This depends on whether the liquid flow is laminar or turbulent.
** Applies to ice cream mixes containing particles of diameter less than or equal to 1000 µm.


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.

It is important that students understand accuracy, precision and error before embarking on research projects and reflect this understanding in reports and dissertations.

There is a free tutorial by Cecil McIntosh on Sophia that explains these concepts and also provide self assessed questions to test understanding.

The editorial group of Wiley is offering Assistant Editor positions based in their Beijing or Shanghai offices in China for their internationally-renowned food science and nutrition journals, including Molecular Nutrition and Food Research. As part of an international team of editors, the focus of this role is on evaluating manuscripts, handling peer review and making decisions on which manuscripts to accept for publication. Link removed.


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