R. Indra and A. Magash
State University of Agriculture, Zaisan, Ulaanbaatar-210153, Mongolia
The milk yield of yak and its hybrid, the 'khainag', is 300 and 470 kg, respectively. However, yak milk has higher density, and fat, protein and sugar contents. The larger diameter of fat globule (5 to 6 μm) makes the separation of butter easier in yak milk than in milk of other animals. Therefore, the yak milk is suitable for making milk cream. Because yak milk is rich in carotene, the butter is of yellowish colour and very delicious. Associated with the high protein content is the high acidity of yak milk. Among the fatty acids of yak milk, the saturated and unsaturated types constitute 22% and 55.2% of the total, respectively. The concentrations of low molecular weight volatile acids and vitamin F in milk of yak and its hybrid are higher than that in cattle. Regarding the differences between the lipid amounts in the yak milk during winter and summer seasons, the technology of butter production suited for the seasons has been developed. Mongolians produce a large range of products from the yak milk. They may be classified into the products of butter, fermented and protein products. Butter products include milk membrane (orom), and yellow and white butter. The fermented products are yoghurt and koumiss (airag); wet and dried curds (aaruul) are the protein products.
Keywords: Amino acids, fat, fat globule, fatty acid, fermentation, hybrid, mineral, protein, sugar, yak
Because of the popularity of yak milk and its products, the milk products made in the areas where the yak is bred are well known throughout Mongolia. The butter pre-processing factories utilise the raw materials from these areas. Baterdene (1961, 1988) has studied the yield and composition of yak milk. These studies reported that the lactation length of yak cows calving in February or March was 283 days, while it was 231 days for yak calving in April. In other words, the length of lactation (and hence milk yield/lactation) depends on the time of calving. The dry matter, fat, protein, sugar and minerals (ash) account for 19.3, 7.89, 5.31, 5.21 and 0.95%, respectively, of yak milk.
Indra (1983, 1997) has studied the technology for traditional processing of milk products in Mongolia in relation to milk quality and has attempted to explain the peculiarities of the technology developed by nomadic livestock farming communities. Lkhagvajav (1978) investigated the lipid components of yak and Mongolian cattle milk in different seasons.
The present study was undertaken to investigate the features of the yak milk composition and technology of milk processing as bases for any future development of industrial-scale processing of yak milk.
Ten cows, similar in their calving periods, milk yields and live weights from yak, Khainag (hybrid) and Mongolian cattle herds were used for the study. Milk samples were taken from each experimental animal during each month of lactation.
The milk composition in yak, khainag and Mongolian cattle is shown in Table 1.
Table 1. Composition of the milk of Mongolian cattle, yak and Khainag.
Parameters (%) |
Mongolian cattle |
Yak |
Khainag |
Density |
29.61 ± 0.060 |
33.08 ± 0.199 |
32.00 ± 0.028 |
Souring |
20.60 ± 0.096 |
21.84 ± 0.052 |
22.30 ± 0.300 |
Fat |
4.28 ± 0.098 |
0.79 ± 0.124 |
5.58 ± 0.143 |
Protein |
3.42 ± 0.030 |
5.03 ± 0.110 |
4.29 ± 0.235 |
Sugar |
4.75 ± 0.020 |
5.10 ± 0.021 |
4.84 ± 0.074 |
Ash |
0.80 ± 0.05 |
0.86 ± 0.009 |
0.93 ± 0.049 |
Dry matter |
13.25 0.104 |
17.78 ± 0.229 |
15.64 ± 0.325 |
The fat content of yak milk was higher than that of native cattle in the highland areas by 58% while the protein amount was higher by 47% (Table 2). The sugar and mineral contents were also higher. As a result, the total amount of dry matter in yak milk was also higher than that of the native cattle. The composition of the Khainag's milk was about the average of Mongolian cattle and yak. The coagulation capacity of the yak and Khainag milk was higher than that of Mongolian cattle by 2%.
Table 2. The amino acid contents of the milk of cattle and yak.
Amino acids |
Mongolian cattle |
Yak |
Cystine + cysteine |
1.17 |
0.90 |
Lysine + histidine |
11.65 |
11.53 |
Arginine |
3.91 |
3.24 |
Aspartic acid |
6.91 |
6.24 |
Serine |
4.02 |
4.24 |
Glycerine |
2.75 |
2.54 |
Clutamic acid |
17.73 |
17.18 |
Threonine |
4.09 |
4.09 |
Tyrosine |
3.41 |
3.53 |
Alanine |
2.73 |
3.20 |
Proline |
2.75 |
2.54 |
Methionine |
2.85 |
2.54 |
Valine |
5.70 |
5.66 |
Phenylalanine |
4.19 |
3.99 |
Isoleucine-leucine |
18.67 |
18.08 |
Total |
93.94 |
19.11 |
A feature of the yak milk is its higher coagulation capacity resulting from high concentration of calcium. This is connected with the higher amount of minerals, particularly salts of phosphoric acid and proteins (Table 3). The areas in which the yak are raised for milk production are famous for yak milk products throughout Mongolia. These areas produce largest amount and highest quality of butter.
Table 3. Mineral composition of milk of yak, Khainag and Mongolian cattle.
Breeds |
Ash (%) |
Calcium |
Phosphorus |
Yak |
0.89 |
130.6 |
106.22 |
Khainag |
0.93 |
134.0 |
134.82 |
Mongolian cattle |
0.88 |
124.91 |
97.82 |
Because the yak and Khainag milk is rich in protein, which has higher clotting and coagulating capacity, forming dense and homogenous coagulum, the milk is suitable for making protein products such as cheese, wet and dried curds. A major protein in the yak milk is casein, which accounts for 5.03% of total protein and 1.5% higher than that in cattle. It is capable of forming a dense coagulum in the presence of both lactic acid and stomach enzymes. Yak milk (132 mg/100 mL) has higher calcium content than cattle milk (124 mg/100 mL). Therefore, yak milk is well suited for cheese, yoghurt and curds, which are protein products.
The amino acid content of yak milk was not different from that of cattle (see Table 2 above). Of course, essential amino acids are the same as those in the milk of other animal species, including glutamic acid, leucine, isoleucine, lysine and histidine.
Because of large diameter of fat globules in the yak milk [5 to 6 µm (1 to 10)], the fat globule is built up for 44 minutes in average (60 minutes in cattle). Due to the large size of fat globules, the loss of butter during separation is lower, and 97% of butter is extracted.
The saturated and unsaturated fatty acids constitute 65.2% and 34.8%, respectively, of the total fatty acids in the yak milk, and they include 22 kinds of fatty acids. The total percentage of low molecular weight fatty, capryne, caprice and caprylic acids, which are responsible for the smell and taste of fat, is 7.2%. Among the saturated acids, palmitin (29.2%) and stearin (14.9%) are dominant. Olein occurs mostly among the unsaturated fatty acids and there are 5.5 to 6.0% multiple bond unsaturated acids or vitamin F. This is found in very little amounts in the milk of cattle (Table 4).
Table 4. Fatty acid contents of butter from milk of cattle, yak and Khainag.
| Fractions of fatty acids | Milk butter | ||
Mongolian |
Yak |
Khainag | |
Saturated fatty acid (C12-C20) |
60.4 |
58.0 |
57.0 |
Low molecular weight |
6.6 |
7.2 |
9.3 |
Unsaturated acids |
33 |
34.8 |
33.4 |
Double bond linoleic, linolenic and arachidonic acids |
2.1 |
5.5 |
5.4 |
The presence of linoleic, linolenic, arachidonic and enozen acids in the yak milk indicates the biological activity of yak milk. There are some seasonal differences in the butter of yak milk. In winter, the amount of volatile acids is higher, while the unsaturated acids are lower compared to summer. As a consequence, the expansion coefficient, melting temperatures and hardening of butter are different during winter compared to summer. Because of higher fat content in the yak milk, the concentrations of fat-soluble vitamins are also higher.
To make Swiss- or Holland-type cheese from yak milk, detailed studies of coagulation capacity, curd composition and types is essential. Such studies are necessary to facilitate the development of new technology of cheese production and to determine what kind of cheeses can be made using yak milk. Mongolians produce many kinds of products from yak milk. They are classified into butter protein and fermented products.
Mongolian technology of milk products is quite developed in relation to the specific ecological and central Asian dry climate with high fluctuations between day and night temperatures and conditions of nomadic livestock farming. Manufacturing of Mongolian milk products does not require any sophisticated equipment.
A layer of protein and lecithin on the milk surface—'orom'—which is formed after 24 hours of keeping in static position followed by boiling of the milk and frequent mixing. Under this layer, fat globules are deposited forming another thick layer. Finally, these layers or milk membrane are picked up, having a bend through the diameter line. The yak milk 'orom' has 20 to 25 mm thickness and is used for daily consumption and for special meals, e.g. for guests. Daily portions of 'orom' are stored in a specially prepared container, and go through lactic and propionic acid fermentation; they are melted to obtain yellow butter. The remainder is called white butter, which consists of protein and fat. This kind of butter is used for food during winter in mixtures with sugar and other products.
The coccus and rod shaped lactic acid bacteria and yeasts in their symbiotic lifestyle are key in the fermentation process. Depending on the temperature and microbe types, two types of products differing in taste and quality can be produced:
This product can either be consumed directly or it can be used for processing wet and dried curds. Because they can be stored for extended periods and easily transported, these products are a kind of protein concentrate and dried food, consumable all year round. To make curd, the yoghurt or koumiss is heated lightly and filtered to collect the curd then wet curd is cut in various shapes and dried. Curdling fresh milk with lactic acid produced another kind of dried curd called 'Eezgii', and the mass is boiled until the milk liquid is evaporated. Then the mass is dried in open air.
To make cheese, the milk of yak is heated up to 84°C and curdled by lactic acid. No microbiological process takes place during production of Mongolian cheese, which is a drained and pressed coagulum. It weighs about 3 to 4 kg and is square with obtuse angles. Cheese is a favourite food of Mongolians and is used in fresh form. To store the cheese, it is cut into thin pieces.
Baterdene T. 1961. Biological and economical quality of Mongolian yak and its hybrid. PhD thesis. Moscow, USSR. pp. 34–41.
Baterdene T. 1988. Economic and biological features of yak and its importance in the economy of MPR. Ulaanbaatar, Mongolia. pp. 23–26.
Indra R. 1983. Milk and milk products. Ulaanbaatar, Mongolia. pp. 46-52, pp. 87–91.
Indra R. 1997. Milk and milk products. Ulaanbaatar, Mongolia. pp. 70–79.
Lkhagvajav B. 1978. Lipido-acidic composition of milk fat of Mongolian yak and khaihags. Journal of Food technology 4:41–43.
