Milk used for making good cheese must meet certain critical physical, chemical and microbial standards. These standards, which should be rigorously imposed when the milk is intended for human consumption, have been widely reviewed in specialized publications. More detailed information on quality control, milk collection and keeping methods may be obtained from the following publications: Ramet, 1985c; Scott, 1986; Robinson, 1990a; Weber, 1985; Lambert, 1988; IDF, 1990. The main points are covered in the following sections.
Milk must be obtained only from healthy animals. Milk from sick animals may contain bacteria harmful to consumers. If the animals have been treated with antibiotics, their milk may include residues whose residual action might inhibit development of lactic acid starters when the milk is processed into fermented dairy products such as cheese.
Colostrum milks, secreted at the beginning of lactation, are not suitable for cheese making because of low casein and high salt levels. They should be avoided for one to two weeks after calving. Camel milk produced by animals under serious water shortage conditions contains abnormally low milk solids and its cheese processing ability is poor. It should be discarded or mixed with milk from other camels that is richer in dry matter or with other milk that is better adapted to cheese making.
The potential vectors of milk contamination are numerous and of various origins. They include: dirty animals, soiled udders, contaminated dairy utensils and cloths and dirty hands of milkers. Strict observance of accepted cleaning and disinfecting procedures is vital to ensure good quality milk and dairy products.
The following rules should be followed:
- be healthy people without open wounds, particularly on the hands;
- wash and dry the hands before milking;
- not handle utensils with dirty hands;
- thoroughly clean and disinfect each utensil in contact with milk;
- work in a clean place or room without dust, insects, manure or stagnant water;
- cool milk rapidly to 0 to 4°C if processing or consumption does not occur within five to eight hours of milking. (Even at these low temperatures, psychrotrophic bacteria may grow. The total raw milk holding period should not last more than 24 to 48 hours, depending on the level of contamination.)
Surfaces that are in contact with milk and dairy products must be efficiently cleaned and disinfected. The average generation time of microorganisms is around 20 to 30 minutes under optimal growth conditions (temperature: 25 to 35°C; pH: 6.65; water activity (Aw): more than 85 percent).
Ideally, the following manual cleaning and disinfecting methods should be followed:
Raw milk always contains microorganisms whose importance and variety depend on the health of the animal, hygiene conditions during milking, the milk collecting system and time-temperature conditions during storage (Ramet, 1985b; IDF, 1990). Among the microbe population, some categories are more dangerous because they may transmit diseases to humans (pathogenic germs) or cause defects in the final product (gas-forming, proteolytic and lipolytic cells). Depending on the extent of microbial growth and subsequent cell concentration, such contamination may cause problems during processing or sensory defects in the finished product (blowing, poor texture, bitterness and rancidity) or lead to the destruction of the product.
Raw milk contains varying quantities of lactic acid bacteria suitable for processing cheese. These bacteria produce the lactic acid required for further draining and acid protection of the curd. This natural acidification of milk is, however, variable in speed and intensity because it depends on factors that are not related to time. As a result, the processing and final quality of the product would not be regular. Heat treatment of milk balances out these unknowns but requires the addition of lactic starters prior to the coagulation phase. For hygiene and technical reasons, heat treatment of camel milk prior to processing into cheese is strongly recommended.
On the basis of cheese-making trials carried out under various conditions with milk from different origins (Ramet, 1987; Ramet, 1990; Ramet, 1994a; Ramet, 1995), it appears that thermizing (62°C for one minute) or pasteurizing (72°C for one minute) are best for microbial stabilization of camel milk and for preventing occasional curd blowing (Table 11). The results show that milk clotting and draining ability are progressively reduced if higher heat treatment conditions are used.
The main features noted during coagulation were a longer clotting time, a decrease in the firmness of the curd and an increase in brittleness. Similar changes noted after heating cow's milk were caused by heat- induced chemical reactions, such as formation of a complex between kappa casein and beta-lactoglobulin and a decrease in soluble calcium content. These reactions decrease the response of the medium to the action of milk clotting enzymes (Webb, Johnson and Alford, 1974; Ramet, 1985a; Eck, 1990).
A progressive decrease in the propensity of the curd to whey off during draining has been noted, related to an increase in the time-temperature conditions used during heating (Figure 9). This development of the coagulum originates mainly from the higher water-binding capacity of the whey proteins caused by heat denaturation. The curd subsequently remains more moist and crumbly and the dry matter losses in the whey increase in relation to the brittleness (Table 11).
With regard to the above observations, it appears necessary to regulate the heat treatment of camel milk according to the total solids content required in the cheese at the end of draining. Milk to be processed into fresh or soft cheese should be heated under low pasteurization conditions (72 to 76°C for 15 to 30 seconds), whereas for production of less moist cheese such as semi-hard and hard types, thermizing at 62°C for one to two minutes only should be carried out.
Another factor to be taken into account when determining heat treatment conditions is the total solids content of the milk. The adverse effects have a more negative effect on milks with lower dry-matter and casein contents than those richer in these components. Camel milk produced in the hot season by animals short of food and water has poor cheese-making capability (see Composition of camel milk on p. 3 and Coagulation on p. 11). Such milk should not be heated, to avoid further reduction of its cheese-making capability. Hygiene and technical risks during processing mean that these poor milks should be rejected. For other milks with higher total solids and casein content, it may be sufficient to balance the time-temperature conditions of heat treatment with the seasonal variation in milk composition. Further experience of cheese making is required to establish these parameters in relation to the other limitations of the cheese-making process, such as yield and taste and texture quality.
The heating equipment must be capable of providing even treatment throughout the milk. Special plates or tubular heat exchangers are best suited for this operation. When a kettle heated over a fire is used for small-scale processing at family or household level, the milk must be stirred continuously during the heating process in order to avoid localized overheating next to the vessel wall.
It must be remembered that acid milk coagulates when heated, leading to precipitation of casein on the heating surfaces. The acidity of the milk should thus be checked by titration or pH meter before heating starts. Milk of more than 0.22 percent titratable acidity or of less than pH 6.50 should be neutralized before heating.
Neutralization can be carried out using sodium hydroxide on the basis that 40 g of sodium hydroxide (NaOH) will neutralize 90 g of lactic acid. The following example illustrates the calculation:
The cheese maker wants to reduce the acidity of 100 litres of milk from 0.30 percent (30° Dornic) down to 0.16 percent (16° Dornic). A simple calculation shows that the total amount of acid contained in the 100 litres of milk is:
0.30 - 0.16 = 0.14 kg of acid
(30°D - 16°D) x 100 kg = 1 400° D = 140 g of acid
The quantity of sodium hydroxide needed to neutralize this amount of acid is:
40x 100/90= 62.2 g NaOH
The procedure used for neutralization is as follows:
The composition of cheese depends mainly on the total solids, or dry-matter content, and the fat content. The total solids content of 100 g of cheese is measured by the weight of dry matter left after evaporating the water in an oven. The fat content is usually determined by the Gerber method, with the result expressed as a percentage of the dry-matter content of the cheese (Fox, 1987; Lambert, 1988; IDF, 1990).
In cheese making, the fat and total solids contents are controlled to ensure standard taste and texture properties. The composition of the cheese may have to comply with national regulations, where they exist.
The amount of fat in cheese is regulated by controlling the fat content of the milk prior to coagulation. The dry-matter content is subsequently adjusted by controlling the factors regulating the draining and ripening of the curd (Ramet, 1985c; Robinson, 1990a). The fat content in the whole milk is higher relative to the average amount of fat required in most cheese varieties. The milk must therefore be partly skimmed. This may be carried out by natural creaming or by scooping off the cream which has risen to the top of the milk after it has stood for a few hours at room temperature. A more efficient method is to separate off a calculated amount of cream in a milk centrifuge. This is known as standardizing and can be carried out either by continuously separating the excess fat or by batch process, mixing calculated amounts of whole and skimmed milk in the cheese vat.
The amount of fat required in the standardized milk is calculated as follows:
FMSM = (FMC x G)/SNFC + FMW
FMSM = fat content of standardized milk;
FMC = fat content of cheese (percentage dry matter);
SNFC = non-fat solids content of cheese (percentage dry matter);
G = coefficient of recovery of non-fat milk solids in cheese (g/litre);
FMW = fat content of whey (g/litre).
The cheese maker wants to standardize the fat content of camel milk to make a cheese with 30 percent fat in total solids. Other information required for the calculation is:
fat content in whole camel milk = 27 g/litre;
G coefficient = 25 g/litre;
FMW = 8 g/litre.
The required fat content of the standardized milk will be:
(30 x 25)/70 + 8 = 19 g/litre
The total amount of fat required in the cheese vat:
100 litres x 19 g/litre = 1 900 g
Batch ratio (whole to skimmed milk):
whole milk: 1 900/27 = 70.5 litres;
skimmed milk: 100 - 70.5 = 29.5 litres.
One of the most critical factors involved in processing camel milk into cheese is its low total solids content and unique casein and calcium composition. In practice, it is possible to use corrective methods, singly or together, to prepare the milk for processing into cheese.
Increasing casein concentration.Different techniques may be used to increase the relative concentration of casein in milk. The aim is to reduce coagulation time and improve the rheological properties of the curd.
Evaporation of milk.In principle, the method consists of concentrating the dry matter in milk by partial evaporation of water. In order to avoid the damaging effects of high heat on curd clotting and draining (see Milk preparation on p. 18), low temperatures (45 to 60°C) should be maintained. Such operations may be carried out at the household level at atmospheric pressure in the open in small containers. At the industrial level, vacuum evaporation is better, because it enables higher outputs, improves yields and reduces costs. In both cases, the optimum concentration is between 15 and 20 percent total milk solids.
Concentration by ultrafiltration.Ultrafiltration is a more advanced procedure for concentrating casein in milk. In view of its widespread industrial use with cow's milk, it should be possible to raise the protein content of camel milk to between 3.6 and 3.8 percent. No definite information or practical experiences have been published about ultrafiltration of camel milk. It is emphasized that ultrafiltration remains a sensitive process requiring thorough cleaning and disinfection procedures, complete safety in feeding fluids to the system and skilled technical staff. Most of the equipment currently available on the market has a very high capacity and is unsuitable for small-scale production. For these reasons, ultrafiltration has to be reserved for industrial-scale production.
Adding milk powder.Fortifying camel milk solids with milk powder improves the clotting time and causes a significant improvement in curd firmness. Camel milk can thus be processed in a better technical condition (Ramet, 1987). The amount of milk powder to be added is around 4 to 8 percent. This hardly alters the taste and texture quality of the cheese and does not increase the cost. Low- and medium-heat powders should be used.
Another interesting alternative could be to use dry milk retentates obtained by ultrafiltration or dehydration. The technology is complex, however; dried retentates are expensive and not readily available.
Production of powder from camel milk has not been investigated, even on a pilot scale (Abu-Lehia, 1994). It is therefore unavailable and milk powder of bovine origin has to be used. The mixture of the two types of milk reduces the authenticity of cheese made from pure camel milk. Local regulations concerning possible adulteration need to be taken into account.
Adding fresh milk from other species. eographically, goats, sheep, zebu cattle and buffaloes are often bred in association with camels. The milks of these animals are suitable for cheese making because of their casein and calcium content. Mixing these milks with camel milk has been suggested as a means of enhancing the processing properties of camel milk for cheese making.
Field trials carried out in Saudi Arabia (Ramet, 1990) and Mauritania (Ramet, 1994b) have concluded that fortifying camel milk with sheep's milk at levels of 10 to 50 percent has a beneficial effect on coagulation and draining:
The positive effects on coagulation and draining are explained by the improved curd structure resulting from the high solids of sheep's milk (28.9 percent) and clotting materials (casein, insoluble calcium). Mixing sheep's milk with camel milk brings considerable benefits to the processing of camel milk into cheese, even when small amounts are used. The simplicity of the method makes it very easy to use on both the small and the industrial scales. As stated above, however, the product loses its integrity as a pure camel-milk product as result.
Adding calcium salts.The presence of ionic calcium is essential to complete the secondary phase of the clotting process and to structure the network of casein micelles leading to curd formation (see Enzyme coagulation on p. 11; Webb, Johnson and Alford, 1974; Ramet, 1985b; Eck, 1990). Because a unique salt balance exists in camel milk, the addition of a soluble calcium salt, such as a chloride or monophosphate, produces a significant reduction in clotting time and reinforces gel strength (Ramet, 1985b; Ramet, 1987; Ramet, 1990; Ramet, 1994a). The positive effect of these salts is explained by the consequent pH decrease (Figure 15), which enhances the proteolytic activity of the milk-clotting enzymes, and by the fact that enrichment in calcium ions generates additional links, which strengthen the cohesion of the casein micelle network (Figure 16).
Depending on the calcium salt concentration, the effect is 15 to 20 percent higher in camel milk compared with cow's milk. Calcium monophosphate is more efficient than calcium phosphate (Ramet, 1985b). From a practical cheese technology standpoint, the addition of calcium salts has to be limited to 10 to 15 g per 100 litres of milk to avoid development of soapy and bitter flavours. These amounts reduce clotting times by 20 to 25 percent compared with control milks (Ramet, 1985a; Farah and Bachmann, 1987; Ramet, 1990; Ramet, 1994a).
In order to ensure uniform dispersion of the calcium salts in the milk and to achieve the required change in salt balance, the calcium salts have to be added at least 30 minutes before the milk-clotting enzyme. If this lead time is observed, the calcium salts have less influence on coagulation (Mohamed et al. 1990).
When milk is heated at the beginning of the manufacturing process to improve cheese quality (see Heat treatment on p. 18), the calcium salts must be added to the milk after thermizing or pasteurizing and subsequent cooling to clotting temperature. The added calcium salts will otherwise be precipitated and their enhancing effect lost.
The calcium salts must be of food grade to avoid bad flavours and toxic minerals in the cheese. For this reason, unrefined salts should not be used. Calcium chloride of cheese-making quality is readily and cheaply available on the market in dried form (powder or granules) or as an aqueous concentrate (510 g/litre). Calcium monophosphate should be used in powder form. It has a lower solubility and a higher price than calcium chloride and is not so readily available.
Adding sodium chloride.Milk is sometimes salted with sodium chloride for protection against spoilage by various microorganisms. The amount of salt required to reduce water activity enough to prevent microbial growth is 4 to 5 percent (Ramet, 1985b). Sodium chloride causes major changes to clotting times depending on the concentration added. At very low rates of up to 0.3 percent, a slight improvement of up to 15 percent for the coagulation process is obtained for rennet and bovine pepsin coagulants. When salting percentages are above these values, clotting times are increased. At rates over 0.6 percent NaCl, coagulation is longer than for unsalted control milk (Ramet, El-Mayda and Weber, 1982; Ramet and El-Mayda, 1984).
The positive effect of sodium chloride at low concentrations is explained by the reduction in pH, which enhances enzyme action. At higher concentrations, sodium chloride has a mainly dissociating action on casein micelles and enzymic proteins (the salting out effect), which adversely affects curd formation.
The effect of sodium chloride on cow's milk is not the same in the presence of different types of milk-clotting enzymes (Hamdy and Edelsten, 1970; Ramet and El-Mayda, 1984). A similar situation has been found for camel milk. Bovine pepsin appears less sensitive to NaCl than calf rennet, particularly at high concentrations (Figure 18).
The rheological properties of gels are also influenced by the presence of sodium chloride in the same manner as clotting enzymes. At the lowest concentrations, firmness is improved and brittleness reduced. At medium and high concentrations, the effects are opposite and cause a decrease in gel strength and an increase in brittleness. These changes are more significant for calf rennet than for bovine pepsin (Ramet, 1990).
Salting camel milk at a concentration of 0.3 percent may thus be recommended to improve clotting. The benefit is limited in practice, however, by the fact that sodium chloride increases water retention in curd and reduces draining ability. The method can therefore only be used for production of moist cheese and some soft cheese (Ramet, El-Mayda and Weber, 1982; Ramet and El-Mayda, 1984; Ramet, 1985c). Whey drained from salted curd contains about 3 g/litre of sodium chloride, which should not affect its economic value.
Experimental work in Saudi Arabia (Ramet, 1985a; Ramet, 1990) and Tunisia (Ramet, 1987) has shown that different commercial milk-clotting products do not all have the same ability to coagulate camel milk (Figure 2). Of the enzymes, bovine pepsin has been identified as the best for clotting camel milk. Calf rennet and milk-clotting enzyme extracted from the mould Mucor mieheihave slightly less effect. Other observations (Gast, Maubois and Adda, 1969; Yagil, 1982; El Abassy, 1987; El-Batawy, Amer and Ibrahim, 1987) corroborate the advantage of pepsin for coagulating camel milk.
A characteristic common to all pepsins is that they are more active than chymosin and rennet in acid media. Clotting activity decreases rapidly at pH levels above 6.3. At the pH of fresh milk (6.65 to 6.75), clotting does not occur. Similar behaviour has been observed in both cow's and camel milk (Figure 19). Results indicate that the milk must be acidified to pH 6.2 to 6.5 prior to coagulation in order to achieve the best effect. It must be noted, however, that such an increase in acidity results in demineralization of the casein micelles, which in turn increases curd fragility and makes draining more difficult. For these reasons, milk to be used for processing into fresh and soft cheeses can be acidified as described above. For semi-hard and hard cheeses, it is advisable to limit acid development in relation to the total solids anticipated in the cheese to pH 6.4 to 6.5 for semi-hard cheese and pH 6.5 to 6.6 for hard cheese.
Pepsin has a high non-specific proteolytic activity, which may produce bitter peptides in the cheese during ripening, depending on the amount of residual milk- clotting enzymes. This is itself conditioned by the pH value and the total proteolytic potential introduced elsewhere into the cheese by microflora. It is well known that bitterness appears more frequently when the pH of the cheese is lower than 5.2 and when the microbial activity is low.
The bitter peptides mainly originate from beta-casein hydrolysis, which is relatively high in camel milk. Observations indicate, however, that the bitterness is no more common in camel cheese than in cheese made from other milk.
No definite information exists of any reactions that could limit the use of pepsin to produce camel cheese. Calf rennet and fungal protease from Mucor miehei ffer lower risks and could thus be preferred to pepsin, in spite of their weaker ability to clot camel milk.
Milk-clotting enzymes are acid proteases whose optimal activity is generally close to pH 5.5 (Ramet, 1985a; Eck, 1990). From the literature, it appears that fresh camel milk pH varies fairly widely from 6.55 to 6.85, depending on origin and local production factors (Farah, 1993; Jardali, 1994). These pH values are not particularly suitable for good clotting. It is thus beneficial in cheese making to acidify the milk slightly at the time of adding enzyme. It can be demonstrated (Figure 19) that increasing milk acidity from pH 6.66 to 6.40 decreases the clotting time by 28 percent, when using rennet, and 70 percent, when using bovine pepsin.
Various procedures can be used to reduce pH value:
When food-grade acid is not available, an alternative practical method could be used which involves adding acid whey (1.2 to 1.8 percent lactic acid) obtained from previous cheese making. Prior to adding the acid whey, the existing lactic acid bacteria present in the camel milk should be destroyed by pasteurizing at 72 to 76°C for one minute to prevent excessive growth during milk processing. This procedure dilutes the concentration of the milk components, however, so it must be limited to small pH adjustments.
Two new methods for adjusting pH value at renneting have recently been developed and used in industrialized countries. The first acidifies the milk with gluconic acid produced from aqueous hydrolysis of glucono delta-lactone (GDL). The second is based on the fortification of carbonic acid in milk by injecting purified carbon dioxide. The gas is readily soluble and induces a rapid pH decrease.
Increasing acidity generates a corresponding demineralization of the casein micelles in addition to the pH decrease. This development, in turn, causes a gradual decrease in curd elasticity and draining ability. The reduction of pH must therefore be carried out with caution using the narrow, well-defined limits for each cheese variety (see Summaries on p. 28).
In some African countries milk, including camel milk, is stored in wooden containers, which are scoured with charcoal or heated over an open fire. It seems that this could cause a small decrease in pH (of 0.1 to 0.2 pH units) resulting from the dispersion of organic acids in the milk. Milk treated in this way, and the resultant cheese, have a characteristic smoky flavour (Mohamed, 1990; Ramet, 1995).
The optimum temperature for most milk-clotting enzymes is around 40 to 45°C. Above this range, the enzyme is progressively deactivated up to 65°C, when denaturation is total (Ramet, 1984; Eck, 1990). Between 25 and 40°C, a linear relationship exists between temperature increase and the reverse of clotting time. Using rennet as a coagulant, for example, will decrease the clotting time of cow's milk by about 70 percent at temperatures within the above limits. There is a similar tendency with camel milk, but the decrease is limited to 50 percent (Farah and Bachmann, 1987).
In practice, it is possible to capitalize on this property in order to reduce clotting time. The degree of reduction is determined by three factors:
The possibility of increasing temperature is feasible, but only by 3 to 5°C.
For most milk-clotting enzymes, a linear relationship exists between clotting time and the reverse of enzyme concentration. If the amount of enzyme is doubled, the clotting time is reduced by half (Ramet, 1985b). In practice, this adjustment should be employed with care, because altering the enzyme concentration upsets the delicate balance between acid and enzyme makeup, which defines any cheese-making process. Overdosage of the milk-clotting enzyme invariably causes a granular curd texture and the development of bitterness resulting from accumulation of bitter peptides.
A further consideration in limiting enzyme concentration is that the clotting ability of camel milk is reduced more than for the milk of cows, sheep, goats or buffalo. As previously mentioned, this situation calls for an increase in enzyme concentration in order to obtain comparable processing times. It is not advisable, however, to increase the clotting enzyme amount significantly.
The chief feature of the camel milk coagulum during draining, even after remedial treatment, is that it depends mainly on the brittleness and the low elasticity of the curd. Physical treatment applied during the earlier stages of draining should thus be carried out with care, to prevent any damage and unwanted curd disintegration.
A well-fortified coagulum is needed at cutting, which must be done with care. These conditions are essential to prevent the curd from disintegrating into small particles that will be lost in the whey. The moulding technique should not cause further curd breakage. Methods used to ensure proper draining depend on the type of cheese to be processed:
These modifications are particularly called for when the milk to be processed has a low total solids content. This situation occurs often in the hot season when milk is collected from animals under feed and water hardship (Ramet, 1990; Ramet, 1991; Ramet, 1994b; Ramet, 1995).
After moulding, subsequent draining of camel milk curd is characterized by several distinctive features:
Cheese yields under experimental cheese-making conditions indicate that the recovery of milk solids in the cheese depends largely on milk origin and cheese type. For semi-hard cheese manufactured in the hot season from milk with a poor dry-matter content, the percentage of solids recovered is low (31.7 percent) and similar to the level measured without corrective treatment (Ramet, 1987). When corrective treatments such as pasteurizing and adding calcium salt are used on milk from intensively managed animals, recovery is improved to 45.7 percent (Table 13).
For soft cheese made from milk produced by camels managed under extensive systems, solids recovery varies from 38.0 percent at the end of the hot season to 42.0 percent at the beginning of the cold season (Ramet, 1994b; Ramet, 1995). When camel milk is enriched with sheep's milk at rates of 30.0 and 50.0 percent, recovery is greatly improved from 33.3 percent to 55.1 and 58.1 percent, respectively.
The recovery of dry matter in fresh cheese is higher than in other cheese, mainly because the whey solids are more strongly held in the curd. For example, when camel milk is processed after pasteurization and addition of modified milk-clotting enzyme and calcium salt, recovery reaches 56.0 percent (Ramet, 1994a).
The weight of cheese produced from 100 litres of milk is dependent on the moisture content of the cheese and the level of recovery of the milk solids. On average, the yield for semi-hard and soft cheese is some 10.5 to 10.7 kg per 100 litres of milk when the milk solids are high (Table 13; Ramet and Kamoun, 1988; Ramet, 1994b). When the quality of the raw milk is poor, yields decrease markedly to as low as 6.7 percent (Ramet, 1987). For fresh cheese made from good-quality milk, the yield reaches 26.0 percent (Ramet, 1994b).
Whey drained from camel milk has a characteristic white colour. Its total solids content averages 6.9 to 7.0 percent, of which 1.2 to 1.3 percent is fat (Ramet, 1987; Ramet, 1994b). The amount of solids loss in whey can be reduced during processing by using milk with high total solids and being careful with mechanical treatment during clotting and draining. The filtration force at draining greatly influences the solids losses, with higher rates producing better recovery and lower fat levels of around 0.6 percent (Ramet, 1995).
The total amount of whey produced during draining is important. It varies as the reverse of cheese weight and comprises between 70 and 90 percent of the quantity of processed milk for fresh, soft and semi-hard cheeses, respectively.
Data on the ripening of camel milk cheese is very limited, because little scientific research has been carried out into this relatively new subject. Only general observations have been made during trials on a laboratory or pilot scale. Very little specific information has been published on ripening time, the main compositional factors regulating enzyme potential or the changes in cheese composition caused by the enzyme reactions.
Experimental results indicate that taste and texture quality develops in a similar way to cheese produced from cow's milk. An important distinction concerns the development of a more crumbly, chalky cheese texture. These properties are probably the result of the lower fat content and reduced water-binding capacity of the casein. Another factor, which has occasionally been reported when the cheese is consumed, is a greasy sensation in the mouth (Ramet, 1987; Ramet and Kamoun, 1988; Mehaia, 1994). This defect is assumed to originate from the fatty acid composition of camel milk fat and from interactions involving mouth temperature and the melting point of the fat.
For cheese ripened for several days in the open at ambient temperature, water evaporation from the curd is deeper and faster in camel milk cheese than in cheese from other milk. These developments lead to the formation of a crusty surface and hard texture, which are probably linked to the specific effects of fat and casein which facilitate the migration of free water towards the surrounding atmosphere. As camel milk cheese is more sensitive to water balance, the relative humidity of the ripening room or container must be accurately controlled at between 90 and 95 percent. Such control is difficult in dry desert environments where the humidity is often as low as 15 to 20 percent (Ramet, 1995).
Another important factor is that the growth of microbial flora involved in ripening is determined by water activity (Aw), mainly on the surface of the cheese. If air humidity drops below 65 percent, surface water activity stabilizes at 0.65, inhibiting development of microorganisms according to their sensitivity to Aw. The development of cheese composition and taste quality ceases and ripening does not progress normally.
For cheese that is mainly ripened by fungal flora composed of Penicillium camemberti Penicillium roquefortiand Geotrichum lactis the visual growth and appearance of the mycelia have been judged satisfactory for various types of cheeses such as Camembert (Ramet, 1987; Ramet, 1990; Mehaia, 1994b; Ramet, 1994; Ramet, 1995), fresh cheese (Ramet, 1987) and semi-hard cheese (Ramet, 1991).
On some batches of hard cheese, slower development of the microflora has been noted. It has not been clearly determined whether this originates from the effect of water activity or from residual activity of the strong antimicrobial capacity of the raw camel milk (Ramet, 1994b; Ramet, 1995).
The taste of cheese made from camel milk varies according to ripening time and cheese type. For fresh cheese consumed immediately after draining and salting without ripening, the taste profile is neutral, without any distinctive characteristic. For young soft cheese and semi-hard cheese, similar results have been found (Ramet, 1987; Ramet, 1994b).
For soft cheese ripened with Penicillium camembertias the dominant flora, a distinctive, original taste develops with time as the chemical transformation of the curd occurs. This flavour, which is completely different from similar cheese made from cow's milk, is accepted positively by testers (Ramet, 1994b; Ramet, 1995).
A slight to moderate bitterness has sometimes been noted in all cheese types during the early stages of ripening. This generally disappears as ripening develops. The origin of the defect has not been clearly identified. It could be caused by the effect of high levels of calcium salts used for improving the coagulation process and/or the accumulation of bitter peptides formed by residual proteolytic activity of the milk- clotting enzymes and the resultant low pH value (Ramet, 1987; Ramet and Kamoun, 1988; Kamoun and Bergaoui, 1989).
The salty and/or bitter taste sometimes detected in some batches of camel milk cheese originates from particular forage species. It has not been determined whether the bitter substances are eliminated with the whey and/or masked by the other cheese flavouring components (Ramet, 1987).