Among the indigenous milk products, khoa occupies first position among various Indian dairy products and it also forms a base for number of sweet delicacies. Khoa is a popular product throughout India and is called by different names in different regions like mawa, khoya, palgova, kava, etc.
Khoa is the product obtained from cow or buffalo (goat or sheep) milk, or a combination thereof by rapid drying containing milk fat content not less than 30 percent on dry weight basis of the final product. Khoa is a heat coagulated, partially dehydrated milk product which is obtained by heat desiccation of whole milk to 65% to 70% milk solids without the addition of any foreign ingredients, mostly in private and unorganized sectors of India. Due to its large-scale consumption nearly six lakh tones of khoa are manufactured annually, which is equivalent to 7% of India’s total milk production.
Chemical and Nutritive Content of Khoa
The market samples of khoa show wide variations in chemical composition. Certain times, the market samples fail to meet the minimum legal standards also. To provide minimum legal standards in khoa, the minimum fat content of 4.4% in cow’s milk and 5.5% in buffalo milk should be maintained.
Khoa is a rich source of energy, about 458 Kcal per100 g of the product. The food and nutritive value of khoa is extremely high. It contains large quantities of muscle building proteins, bone forming minerals, and energy giving fat and lactose. It is also expected to retain most of the fat-soluble vitamins A and D, and also fairly large quantities of water soluble B vitamins contained in the original milk.
Varieties of Khoa
There are three distinct varieties of khoa. They differ in their composition, body and textural characteristics and end use.
This variety is identified as a circular ball of hemispherical pat with compact mass, homogenous and smooth texture. It is characterized by pleasant and cooked flavor and is generally devoid of objectionable tastes like burnt, acidic etc. For production of pindi variety of khoa, heating is continued after rabri stage and with the help of a wooden ladle the soft grains are crushed, and the mass is worked out to a smooth textured product. After cooling, the khoa is molded into hemispherical molds to give its shape.
It is a raw (katcha) khoa characterized by loose but smooth texture and soft grains and sticky body. Dhap variety carries highest percentage of moisture over other varieties of khoa. For preparing dhap variety of khoa the heating should be stopped at rabri stage (thick mass) and leaving the product without much working.
This is characterized by the granular texture with hard grains of different sizes and shapes embedded in viscous serum. Slightly sour milk is preferred in the manufacture of this variety as it yields granular texture. Generally, the milk that is left over after the preparation of other varieties of khoa is converted into danedar variety of khoa. Sometimes citric acid (0.05 to 0.1%) or sour whey is added to milk at boiling stage to get granular texture.
Factors affecting the quality of Khoa
Type of milk:
Buffalo milk is generally used instead of cow milk for the manufacture of khoa due to its higher yield, softer body, and smooth texture. The khoa manufactured from cow milk have dry surface, yellow color, sticky and sandy texture.
Amount of free fat:
An optimum amount of free fat is necessary for desirable body and textural properties of khoa.
Total solid level:
There is significant positive correlation between total solid level milk and instrumental hardness, gumminess, and chewiness of khoa.
Working of Khoa:
The formation of large lactose crystals can be reduced through working of khoa when compared to un-worked khoa and working results in no perceived sandiness upon storage.
Equipments Used for manufacturing of khoa
Khoa is generally manufactured by halwais by continuous boiling of milk in a shallow iron or stainless-steel vessel to remove moisture. Traditional method used for the preparation of khoa has several disadvantages like poor and inconsistent quality and limited shelf life of about 5 days at 30°C.This leads to the attempts for up-gradation of the technology used for the manufacturing of khoa and following equipments were invented for the large-scale production of khoa.
1. Continuous khoa making machine
It consists of a preheating cylinder and two cascading pans. The preheater is a steam jacketed cylinder containing rotary scrapers which rotate at 120 rpm. The cascading pans are covered steam jacketed pans with open holes provided with spring loaded reciprocating type scrapper knives operating at 30 strokes per min. The milk is taken into the preheater and heated by steam at 3 kg/cm2 pressure. Here the milk is concentrated to about 30 to 35 per cent of total solids within 10 to 12 min. From the preheater, the milk enters the first cascading pan. Here the milk is further concentrated to about 50 to 55 per cent total solids within 7 to 8 min. The product then moves to the second cascading pan where its concentration is raised to the desired level i.e., 65-70 percent in 6 to 7 min. The steam pressures maintained in the two pans are 2 kg in this machine. The steam requirement is 50kg/cm2 and electric power requirement is 4 KW per hour.
2. Scraped surface conical vat
A mechanized scraped surface heat exchanger with a conical vat process is developed for the batch production of khoa. Forty kg concentrated or 80 kg whole milk can be taken per batch which takes about 14 min and 50 min respectively. Steam pressure used is 1.5 kg/cm2. Product losses are high in this machine.
3. Contherm- Convap System
Attempts were made to prepare khoa on Contherm-Convap system which was developed by Alfa-Laval. This unit consists of two parts, a Contherm for heating the feed to about 95°C and Convap for concentrating milk to desired milk solids level. Concentrated milk with 35- 40%T.S. at the rate of 300-350 kg per hour can be fed to the machine. The steam pressures employed are 3 kg /cm2 in Contherm and 4 kg/cm2 in Convap.
4. Thin film scraped surface heat exchanger (TSSHE)
This machine has three jacketed cylinders placed in a cascade arrangement. This facilitates easy transfer of milk from one cylinder into the other. The scrapper speeds are 40, 55 and 69 rpm for the 1st, 2nd & 3rd stage respectively. The operating steam pressures used are 2.0 & 1.7 & 1.5 kg/cm2 in respective stages. One roller is used in the last stage in place of scraper blade which kneads the khoa to improve its body and texture. The first stage raises the milk solids level from initial 15 to 25 percent, the second stage to 50 percent and the third stage to 65-70 percent. The machine converts 50 kg of milk into khoa per hour at the operating pressures, specified. However, the capacity depends on the milk flow rate, steam pressure, total solid concentration of feed and final moisture required in the product. It is claimed that use of concentrated milk improves the capacity of the machine.
5. Inclined scraped surface heat exchanger (ISSHE)
An inclined scraped surface heat exchanger was developed for the continuous manufacturing of khoa. A scraper assembly is so built as to combines the functions of scraping and conveying. The SSHE has 3 jackets which operate at 1.0, 1.5 and 1.0 kg/cm3 respectively. Milk is previously vacuum pre-concentrated to 40 – 55% T.S and fed at the rate of 60-80 lit/hr. Feed temperatures between 10 – 80°C can be employed. Rotor speed used is 40 to 80 rpm.
Although so many technologies are developed for the production and storage of khoa, there is a still a need of investigation of chemical and physical aspects during manufacturing of khoa in order to understand factors responsible for quality. And all the known technologies of manufacturing of khoa should be transferred to small holder farmers who are the major contributors of milk production in India. So that they can increase their prices of products by producing products which will meet the modern quality standards