Predicting the shelf-life of cottage cheese

Monday 02 Feb 15


Paw Dalgaard
DTU National Food Institute
+45 45 25 25 66

New mathematical models that predict the growth of listeria and lactic acid bacteria in different types of cottage cheese can be used by producers to determine the shelf-life of their products. The models have been developed in a PhD project at the National Food Institute, Technical University of Denmark. The project results can also be used as a starting point for developing predictive models for microorganisms in other fermented products.

Disease-causing listeria bacteria may be present in food. If the bacteria are present in large numbers in products that are not heat-treated before consumption, they can lead to the serious disease listeriosis.

Although cottage cheese has not been linked to outbreaks or cases of listeriosis, cottage cheese producers must be able to document that their products comply with microbiological criteria for listeria bacteria. EU legislation allows producers to use mathematical models to document that their products live up to the requirements.

New models developed

In her PhD project at the National Food Institute Nina Bjerre Østergaard has developed models that predict growth of both listeria bacteria and the lactic acid bacteria, which ferment cottage cheese and give it aroma.

Lactic acid bacteria in cottage cheese inhibit the growth of listeria bacteria and Nina Bjerre Østergaard has included this effect in her growth models. The models also take into account other parametres which have an effect on the development of listeria and lactic acid bacteria, such as the effect of storage temperature, pH, salt, lactic acid and sorbic acid.

At the start of the project there were no models which could predict the growth of both lactic acid bacteria from the starter and aroma culture used in the cottage cheese and any listeria bacteria present.

The new models can be used to determine a safe shelf-life for cottage cheese, and new mathematical models for the growth of spoilage bacteria in cottage cheese are under development at the National Food Institute.

Potential for development of further models

The work involved in developing predictive models is comprehensive and requires large amounts of data. It is therefore important that the results from Nina Bjerre Østergaards project can be used as a starting point for developing models that can predict the growth and activity of microorganisms in other fermented foods.

Read more

Download a summary of Nina Bjerre Østergaard’s PhD thesis: Predictive Food Microbiology – new tools for risk assessment and dairy product development (pdf). The PhD project was funded by Arla Foods.

A copy of the PhD thesis is available at the National Food Institute. Once the thesis articles have been published the entire thesis will become accessible on Please send an email to if you wish to be notified when this happens.