Some cows better at cheese than others

The milk from some cows is better suited for cheese production than milk from other cows. Scientists at the University of Aarhus are investigating the reasons why.

Some cows’ milk is better suited for cheese-making than milk from other cows. Which traits in the milk are responsible for the difference and why this difference exists are being investigated in a three-year PhD project at the Faculty of Agricultural Sciences, University of Aarhus.

The suitability of milk for cheese-making depends on its ability to coagulate. This is where the differences from cow to cow lie. If the milk does not coagulate properly, it cannot be processed into cheese.

"Results from an earlier Danish-Swedish research collaboration regarding milk protein composition and cheese yield showed that a surprisingly large proportion of the cows in the study – both the Danish and the Swedish cows – produced milk that was unsuitable for cheese-making because the milk had a poor ability to coagulate. We would like to investigate if it is a general problem in Denmark and, if that is the case, how big the problem is", explains PhD fellow Pernille Frederiksen from the Department of Food Science at the Faculty of Agricultural Sciences.

Initially, Pernille Frederiksen has screened milk from all 151 cows in the herd at the Danish Cattle Research Centre in Foulum. The herd consists of the dairy cattle breeds Jersey, SDM (Holstein) and RDM (Red Danish). The milk was investigated for its ability to coagulate, which can be described using three factors: how quickly the milk starts to coagulate after adding enzyme (rennet), how quickly the coagulum builds up, and how firm the final gel-structure becomes.

"The milk from the Jersey cows had the best ability to coagulate evaluated on the basis of the three factors. Jersey milk coagulates earlier, the process is faster and the final structure is firmer than with milk from the other two breeds", says Pernille Frederiksen.

Several factors at work

There is, however, also a large variation within the breeds. Much of this variation in the milk between cows can be ascribed to factors such as the cow’s general health, feeding strategies, the cow’s stage of lactation, and the number of calves the cow has given birth to (parity). In all likelihood, another important contributor is genetic variation.

"We have only found milk with a poor ability to coagulate in the group of SDM cows. The milk from some of these cows always coagulates poorly, apparently independent of changes in feeding strategies, parity and lactation stage. It cannot be ruled out that breeding for increased milk yield has impaired milk quality", says Pernille Frederiksen.

The protein content of milk or, more precisely, the amount of casein, and the ratio between the four types of milk casein play an important role for the milks ability to coagulate and, thereby, its ability to turn into a nice, firm cheese. With the PhD project Pernille Frederiksen will take an even closer look into the composition of the milk and investigate the protein composition, the genetic profile of the different types of casein, the calcium and magnesium contents, and other chemical factors.

Even if it turns out that only a small proportion of cows produce milk with a poor ability to coagulate, then it is still unsatisfactory for the cheese-making process.

"By mixing good and poor milk we obtain average milk for cheese-making", Pernille Frederiksen points out.

"It would be good if we could provide the dairy industry with the possibility of pre-treating the ”poor” milk in some way, or give the farmers the possibility of doing something in at the primary production site. If we can find a parameter that we can adjust, then it would be possible to reduce coagulation problems. We will also investigate the effect of milk storage and dairy plant processes that may be important for milk coagulation", she explains.

The project is being carried out in collaboration with Arla Foods, the Danish ingredients company Chr. Hansen and the Danish Cattle Research Centre, with senior scientist Lotte B. Larsen, Department of Food Science, as the supervisor.

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Some cows better at cheese than others