Methods of processing camel milk into cheese

To produce high quality cheese, it is necessary to follow routine practice common to the production of all cheese types. Only the basic steps are outlined below. For more detailed information, reference should be made to specialized publications on the subject (Alais, 1984; Veisseyre, 1975; Ramet, 1985c; Scott, 1986; Fox, 1987; Robinson, 1990a; Eck, 1990). Later in this chapter, processing methods for the main types of camel milk cheese are summarized.

GENERAL GUIDANCE

Basic milk-processing parameters

To achieve a good-quality product, the following recommendations should be followed:

• select milk with good chemical and microbial quality;
• make the cheese in a clean, dust-free environment;
• use properly cleaned and disinfected utensils;
• employ healthy, clean, trained staff;
• enhance the processing capability of camel milk by corrective treatment such as heating and/or adding solids and calcium salt (see Milk preparation on p. 18);
• systematically check the main processing factors controlling production;
• use only additives (lactic starters, milk-clotting enzymes, salts, etc.) of food-grade standard with good chemical, microbial and technical properties;
• store heat-sensitive additives under refrigeration to limit activity loss;
• keep perishable raw materials and manufactured products under cool conditions and protected from light, dust and rodents;
• reject defective or questionable raw materials and products.

Preparing and using lactic starters

Using the right lactic starter ensures authentic taste and hygienic quality. For cheese made from raw milk, lactic starter addition is recommended to boost the natural population of lactic acid bacteria and inhibit harmful flora such as coliforms and psychrotrophic and pathogenic bacteria. For cheese made from heat-treated milk, lactic starter addition is mandatory to develop proper acidity, drainage and acid preservation of the curd.

Lactic starters can be prepared by simple methods adapted either for household or for industrial production. The recommended method of preparation is as follows:

• select the growth medium, which can be either fresh milk with good bacteriological and chemical quality or reconstituted milk obtained from dissolving 10 percent skimmed milk powder in potable water;
• pour the reconstituted milk into containers for sterilization;
• sterilize the milk at 100 to 120°C for ten to 20 minutes;
• cool down to the incubating temperature;
• inoculate the milk under aseptic conditions with the mother culture at the rate of either 0.5 g of dry culture per 0.5 to 1 litre, or 20 ml of liquid culture per 0.5 to 1 litre;
• incubate in an incubator or at room temperature: mesophilic starters at 25 to 35°C for eight to 12 hours, thermophilic starters at 42 to 45°C for two to four hours;
• halt incubation when the acidity reaches 0.7 to 0.9 percent lactic acid or pH 5.0 to 5.5;
• cool down and keep the starters under refrigerated conditions (0 to 4°C) until used;
• avoid long storage periods, which reduce lactic acid bacteria viability;
• keep the mother cultures at deep freezer temperatures (-40 to -80°C).

Adding cheese-ripening moulds

Some types of cheese are traditionally ripened with moulds that develop either on the surface (fresh, soft and some semi-hard cheeses) or in the body of the cheese (blue cheeses). Traditionally, the uptake of moulds occurs through natural inoculation when the cheese is left out in the ripening room, which is full of spores. This method is risky, however, and causes inconsistency in appearance and taste of the cheese. It is better to use a more controlled inoculation of commercially available complementary exogenous cultures, obtainable in dried or liquid form.

The dominant organisms in the surface flora are strains of Penicillium, Geotrichum and, occasionally, Mucor. These moulds are often also associated with yeasts and bacteria. Penicillium camemberti is widely used and gives a typical white appearance to many soft cheeses, such as Camembert or Brie, and to some semi-hard cheese such as White Tomme. Penicillium roqueforti is the typical mould that develops in blue cheeses, growing in the holes in the cheese curd.

Inoculation of spores is carried out by two methods:

• in the milk prior to coagulation by mixing an appropriate quantity of commercial strains;
• on the surface of the salted cheese, either by soaking in a solution of spores in sterile water or by spraying the solution over the whole surface.

Equipment used for inoculation must be thoroughly cleaned and disinfected to avoid contamination by spoilage organisms. The spore concentration is adjusted according to the method given by the manufacturers.

Because the moulds used in cheese ripening are highly aerobic, the cheese is placed on trays or wooden boards, which allow good all-round surface aeration. During ripening, the cheese is regularly turned to ensure even growth of the mycelium. Other environmental factors also need to be closely regulated to optimize mould development. The temperature is usually set between 12 and 14°C, except for blue cheese when it is set at 6 to 7°C. The relative humidity is set between 85 to 95 percent, depending on the sensitivity of the microflora to water activity. Under these conditions, mould growth is quite slow. The mycelium becomes visible after four to six days; full development takes up to 15 to 25 days.

The proteolytic and lipolytic potential of mould enzymes is important and influences significant biochemical changes in the composition and taste of the cheese.

Characterizing and using milk-clotting preparations

The activity of commercially available milk clotting preparations is determined in cheese making by clotting strength, which corresponds to the ratio between a defined amount of the preparation (volume for liquid preparations, weight for dried preparations) and a defined amount of milk to be clotted under precise time-temperature conditions. The standard reference used in Europe indicates that 1 kg of powdered rennet, labelled with a strength of 1/150 000, will coagulate 150 000 litres of milk at 35°C within 40 minutes.

The strength of liquid preparations declines slowly at ambient temperature (15 to 45°C) and refrigerated storage (0 to 6°C) is recommended. Dried preparations are less sensitive, but refrigeration is advisable for prolonged periods of storage.

The clotting enzyme quantities indicated in the following summaries for processing camel milk into cheese are given with reference to enzyme preparations with a strength of 1/100 000. When preparations with different strengths are used, the amount should be corrected according to the strength ratio.

SUMMARIES

The following summaries of making the main cheese types are based on production trials in the field carried out during missions supported by FAO. The processing summaries are based on laboratory experiments in Saudi Arabia (Ramet, 1985a; Ramet, 1990), pilot production in Tunisia (Ramet, 1987) or commercial production in Mauritania (Ramet, 1994b; Ramet, 1995).

The results indicate that camel milk is not readily processed into cheese compared with milk from other dairy animals. This results mainly from its low total solids content, unique composition and casein properties. Its suitability for cheese making decreases significantly in the hot season, when camel milk production is influenced by water and feed availability.

The summaries have been modified to cover processing of poor-quality milk. It is thus recommended that both heat treatment and calcium salt enrichment be employed. To effect the changes set out in Chapter 3, the other corrective steps may be applied. It is also crucial to stress that these additional corrective steps become less essential as the quality of the camel milk for processing improves.