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MLA Refrigeration Index Calculator

What is the Refrigeration Index?

The Refrigeration Index (RI) is an index for the log growth of E. coli. It predicts the expected growth of E. coli on meat from temperature and other data. The model has values for pH, water activity and lactate concentration which in addition to temperature, all affect the growth rate of E. coli. The current RI model allows for the user to enter data on temperatures of the product over time. The other parameters are set by choosing the type of product.

RI has replaced the previously termed Hot Boning Index (HBI) and will now be used more broadly than the HBI to assess effectiveness and regulate meat refrigeration processes throughout the Australian industry.

The central idea of the RI is to measure the performance of the chilling process until all the sites of microbiological interest are at or below 7C. This is the temperature at which E. coli and Salmonella stop growing.

It is important to note that the RI, as an indication of the effectiveness of refrigeration, is NOT a prediction of the number of E. coli in the product.

Regulations Concerning the Refrigeration Index

The Refrigeration Index (RI) is a term used in the Australian Export Control (Meat and Meat Products) Orders 2005.

The definitions included in the new Export Control (Meat and Meat Products) Orders 2005 are:

“Refrigeration index means the value obtained by using a recognised predictive model to calculate the potential growth of E. coli at the site of microbiological concern”; and
“Refrigeration index criteria means the criteria applied to the refrigeration indices to assess a chilling process.”
Section 11 of the EC(MMP)Os sets out the criteria for achieving the RI:
Achieving the refrigeration index criteria
11.1 To achieve the refrigeration index criteria (which implies…the control measures specified in the approved arrangement must be such that):
            (a)        the refrigeration index average is to be no more than 1.5; and
            (b)        80% of refrigeration indices are to be no more than 2.0; and
            (c)        no refrigeration index is to be more than 2.5.
Note:    for the meaning of refrigeration index see suborder 8.1

The criteria for RI apply to any refrigeration process for carcases and carcase parts, which means all carcases, primal cuts, manufacturing product and offal items.

The site of microbiological concern depends on the type of product in question e.g. it is the surface for carcases, the thermal centre of bulk-packed meat and offal and the surface of vacuum packaged cuts at a position as close as possible to the thermal centre of a carton.

The refrigeration index criteria must be achieved for the whole process from carcase chilling to cooling boned meat to 7C at the site of microbiological concern.

Download the MLA Refrigeration Index Calculator installation file (12 MB)

Download Explanatory Notes (55 KB)

Download Hot Boning Report (710 KB)

Download Microbiological Growth on Offal During Cooling Report (354 KB)

The Predictive Model

The predictive model used in this calculator was developed by Assoc Prof Tom Ross and colleagues at the University of Tasmania. The model has been published:

Ross, T., Ratkowsky, D. A., Mellefont, L. A. and T.A. McMeekin, T. A. (2003)
Modelling the effects of temperature, water activity, pH and lactic acid
concentration on the growth rate of Escherichia coli. Int.J.Food Microbiol. 82:33-44.

An evaluation of the model against data in the literature has also been published:

Mellefont, L.A., McMeekin, T.A. and Ross, T. (2003) Performance evaluation of a model describing the effects of temperature, water activity, pH and lactic acid concentration on the growth of Escherichia coli. Int.J.Food Microbiol. 82:45-58.