Dairy Sheep Symposium - the Department of Animal Sciences ...

FACTORS AFFECTING THE QUALITY OF EWE’S MILK
Roberta Bencini
Animal Science, Faculty of Agriculture, The University of Western Australia,
Crawley, Western Australia, Australia
Introduction
The milking of sheep for dairy production is relatively new for some countries, such those
found on the American continent and in Oceania, so that the knowledge in the field is scarce. By
contrast, in some countries it is a very traditional industry, such as that found in the Mediterranean
countries, where it has been practiced for thousands of years and until recently did not have
a strong scientific background. It is only since the mechanical milking of sheep was introduced
in France in 1962, that research on sheep milking has been undertaken in most European countries
where sheep are kept for dairying (Purroy Unanua 1986). This has produced a body of
literature, but it is published mainly in languages other than English.
This paper examines the factors affecting the quality of sheep milk for its transformation into
dairy products, particularly cheese.
What is meant by quality of sheep milk?
Most of the sheep milk produced all over the world is transformed into cheese. Some sheep
milk yogurt is produced in Greece, and fresh sheep milk is consumed rarely. For this reason, the
quality of sheep milk relates to its capability to be transformed into high quality dairy products,
and to produce high yields of these products from each litre of milk. This is often described as
the processing performance of the milk.
The processing performance of milk could be measured by making batches of cheese by a
standard method, allowing it to mature for the required time (up to 6 months in the case of some
hard cheeses such as the Pecorino Romano) and determine the important features in the outcome
of the cheese such as yield, composition and taste. However, the amount and quality of cheese
that can be obtained from each litre of milk depends mainly on the clotting properties of the milk
(Ustunol and Brown 1985; Buttazzoni and Aleandri 1990; Cavani et al. 1991). These are the
renneting time, the rate of curd formation or rate of firming and the consistency of the curd. For
this reason milk clotting properties have been widely used by researchers to assess the processing
performance of milk.
The clotting properties of milk are affected by the composition of the milk (Chapman 1981;
Storry et al. 1983; Anifantakis 1986, 1990), by the microbiological quality of the milk, by its
somatic cell count (Pulina 1990; Kalantzopoulos 1994) and by the cheese making process itself
(Alais 1974).
The relationships linking the milk and the outcome of the cheese are represented schematically
in Figure 1. Cheese makers have some control over the clotting conditions, and can vary
pH to achieve the desired acidity by varying the percentage of inoculum of starter cultures
(Cogan and Hill 1993). They can also standardise the fat content (Dolby 1971; Kalantzopoulos
1993) or increase the amount of soluble calcium in milk by adding calcium chloride (Fox 1993).