In this article we will discuss about:- 1. Introduction to Khoa 2. Definition of Khoa 3. Classification 4. Composition, Food and Nutritive Value 5. Methods of Production 6. Physico-Chemical Changes in Milk on Conversion into Khoa 7. Market Quality 8. Yield and Overrun 9. Packaging, Storage and Marketing 10. Keeping Quality 11. Type of Spoilage 12. Judging and Grading 13. Uses.
Contents:
- Introduction to Khoa
- Definition of Khoa
- Classification of Khoa
- Composition, Food and Nutritive Value of Khoa
- Methods of Production of Khoa
- Physico-Chemical Changes in Milk on Conversion into Khoa
- Market Quality of Khoa
- Yield and Overrun of Khoa
- Packaging, Storage and Marketing of Khoa
- Keeping Quality of Khoa
- Type of Spoilage in Khoa
- Judging and Grading of Khoa
- Uses of Khoa
Introduction to Khoa:
Khoa constitutes one of the two chief bases (the other being chhana) for preparing indigenous sweets. The production of khoa in India in 1966 was estimated to be about 4.9 per cent of total dairy production and 8.7 per cent of the milk used for manufacture of milk products.
Today, the total khoa production may be estimated at over 300 million kg., valued at Rs 300 crores at the present rates. The preparation and use of khoa are confined mostly to the northern and western regions of the country. By far the largest amount is contributed by Uttar Pradesh, where nearly 36 per cent of the country’s total khoa production takes place.
Definition of Khoa:
Khoa/Khava/Mawa refers to the partially dehydrated whole milk product prepared by the continuous heating of milk in a karahi over a direct fire, while also constantly stirring- cum-scraping by using a khunti till it reaches a semi-solid (doughy) consistency. Thereafter, the pan-contents are removed from the fire and worked up into a solid mass known as khoa-pat.
According to the PFA Rules (1976), khoa is the product obtained from cow or buffalo (or goat or sheep) milk, or a combination thereof, by rapid drying. The milk fat content should not be less than 20 per cent of the finished product.
Classification of Khoa:
Three main types/varieties of khoa, viz., Pindi, Dhap and Danedar, are received in Delhi, which is the biggest khoa marketing centre in the country. These types differ in quality and also in price. All of these varieties are in demand and are required for specific types of sweets, as shown in Table 11.3.
Composition, Food and Nutritive Value of Khoa:
The chemical composition of khoa depends mainly on the initial composition of milk, the degree of concentration of the milk solids and the losses or gains in handling. An average chemical composition of fresh, laboratory-made whole-milk khoa is given in Table 11.4. A few workers have also reported on the chemical composition/quality of market samples of khoa.
Food and Nutritive Value:
Containing all the milk solids in an (approximately) four-fold concentration, the food and nutritive value of khoa is very high. It contains fairly 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.
Methods of Production of Khoa:
(a) Existing Trade Practices:
Normally 2 to 3 kg. or more of milk (preferably buffalo) is taken per batch and boiled in a karahi (of different sizes and shapes) over a brisk non-smoky fire. The milk is stirred vigorously and constantly with a circular motion by a khunti. During this operation all parts of the pan with which the milk comes into contact are lightly scraped to prevent the milk from scorching.
Constant evaporation of moisture takes place and the milk thickens progressively. So far the process is similar to kheer- making. However, no sugar is added and milk-dehydration continues. At a certain concentration (cow milk 2.8; buffalo milk 2.5), heat-coagulation of milk proteins begins and the concentrate becomes progressively ‘insoluble’ in water.
This stage is marked by an abrupt change in colour. The heating is continued with greater control hereafter and the speed of stirring-cum-scraping increased. Soon the viscous mass reaches a semi-solid/pasty consistency and begins to dry up. Very close attention is paid to the last stages.
The final product is ready when it shows signs of leaving the bottom and sides of the karahi and sticking together. The khoa-pat is invariably made after removing the pan from the fire and working the contents up and down into a single compact mass; it is generally marketed in different sizes and shapes.
(b) Improved Method:
This involves consideration of- equipment; conditions of dehydration, and quality of milk.
(i) Equipment:
The karahi and open-fire combination can conveniently be substituted (in organized dairies) by a stainless steel jacketed-pan/kettle, in the jacket of which either steam or water may be circulated as required. This will not only provide greater control over the dehydration process, but also a non-smoky heating medium. The standard iron-stirrer, flattened at one end for stirring-cum-scraping, is normally used.
(ii) Conditions of Dehydration:
The physico-chemical quality of khoa is influenced by the conditions of dehydration which include- temperature of dehydration; speed of stirring daring dehydration; extent of dehydration, and amount of milk taken per batch for dehydration.
In order to obtain a desirable body and texture in khoa, the milk should be kept boiling till it assumes a pasty consistency and then the temperature lowered to 85 ± 3°C till the pat-formation stage. During the entire dehydration process, milk should be stirred at 96-100 rpm.
The dehydration should be stopped when the pan- contents start leaving the pan-surface and show a tendency to stick together. The amount of milk handled per batch should vary between one-fourth to one-fifth of the total capacity of the pan used.
(iii) Quality of Milk:
This also influences the quality (body and texture) of khoa. Under this factor are included- type of milk; fat level of milk; acidity of milk; adulteration of milk, and homogenization of milk.
For khoa production, buffalo milk is preferred since it yields a product with a soft, loose body and smooth, granular texture— both of which make it highly suitable for the preparation of top- quality khoa-sweets. Buffalo milk also gives a greater yield of khoa when compared with cow milk.
A minimum fat level of 4 per cent in cow milk and 5 per cent in buffalo milk is necessary in order to obtain a desirable body and texture in the khoa, so as to make it acceptable for use in sweet-making. A fat level lower than the above results in an undesirably hard body and coarse texture in the finished product; on the other hand, a higher fat level improves the quality of khoa made.
Fresh sweet milk yields the best results, while developed acidity in milk progressively tends to produce an undesirably sour flavour and coarse texture in the khoa, which is thereby rendered unsuitable for sweet preparation. Neutralization or stabilization of acid milk improves the texture, but does not improve the flavour of khoa made.
Adulteration of milk with starch hardens the body of the finished product (which is rendered less suitable for sweet-making due to an overall excessive starch content). Homogenization of cow/buffalo milk produces a softer body in khoa as against unhomogenized milk; the khoa from homogenized milk also shows lower fat leakage, less browning and a reduced patting tendency as compared to that obtained from unhomogenized milk.
(c) Continuous Method:
In order to overcome the drawbacks of the existing batch method of khoa-making, a continuous khoa- making machine for large-scale production of khoa was designed and developed (1968). The preliminary trials with a prototype machine have shown promising results (1970). The machine is undergoing further improvement.
Equipment Prototype:
This consists of the following essential parts:
1. A steam-jacketed drum heater with a rotary scraper and milk outlet valve;
2. Two open steam-jacketed pans with outlet valves;
3. Two sets of scrapers for the pans, and
4. A power drive for the scrapers.
A cover is provided over the pans to prevent any dust or dirt falling into it.
Whereas the rotary scraper works on the principle of centrifugal force, the pan scrapers are of the spring-loaded reciprocating type. The steam supply line is connected to the drum heater and the pans.
There are three separate regulating valves to control and supply steam to the heater and pans, which are in turn provided with separate steam inlets and condensate outlets. A pressure gauge is provided in the steamline. The whole equipment is supported by stands.
Principle:
The milk is continuously heated in the steam- jacketed drum heater, wherein it is partially concentrated. This is followed by further heating and concentration of the milk, in open steam-jacketed pans till a viscous semi-solid consistency is obtained and the khoa is removed mechanically. Power-driven scrapers provided in the drum heater and in the open steam-jacketed pans, scrape the milk vigorously to prevent it from scorching and burning.
Operation:
The equipment is first cleaned and sanitized, the safety valve pre-set at a prescribed pressure (3.5 kg sq. cm.), all bearing points lubricated with a vegetable oil (or ghee), the scraper- springs properly tightened for smooth operation and all scrapers run for a few seconds with water to test performance.
The milk outlet valve of the drum heater is then closed and its milk inlet valve opened to admit 10-12 litres of milk. The rotary scraper is started and the steamline valve for the drum jacket opened gradually. The milk is boiled vigorously for 10-12 minutes, when it is concentrated about 2.5 times. Now the milk outlet valve is opened and the concentrate flows into the first pan. Simultaneously, more milk is drawn into the drum heater for boiling.
In the first pan, the reciprocating scraper is switched on and the steamline valve in the pan-jacket opened gradually. The milk is heated here for 7-8 minutes, when the total concentration reached is about 3-5 times. Now the first pan outlet valve is opened and the milk concentrate advances to the second pan, through the pushing action of the scrapers.
The second pan works on the same principle as the first. In the second pan, the milk is heated for 6-7 minutes and a final concentration of about 4.5 times obtained. The khoa outlet valve of the second pan is opened and the viscous semi-solid mass of khoa is pushed out mechanically by the scrapers and collected in a container held underneath. The process is continuous.
Note:
The finished khoa usually has a moisture content of 33-37 per cent; a lower moisture level comes in the way of mechanical removal.
Advantages Claimed:
1. Khoa can be made on a large scale under hygienic conditions;
2. Considerable saving in man-hours and human drudgery is made possible.
Note:
The economics of khoa-production with the prototype continuous khoa-making plant have been worked out.
(d) Miscellaneous Methods:
(i) The utilization of aged atmospheric roller-dried skim milk powder and white butter or ghee for the production of khoa of an ‘acceptable’ quality has been standardized.
(ii) The feasibility of using vacuum-concentrated milk for khoa- making has been worked out. It was found that a milk concentrate containing up to 31 per cent total solids produced satisfactory khoa.
Physico-Chemical Changes in Milk on Conversion into Khoa:
These are:
(a) Change of State:
From liquid milk to solid khoa (due to considerable dehydration).
(b) Change in Intensity of Colour:
From ‘light’ to a ‘more intense’ shade of colour (with a tinge of brown).
(c) Homogenization of Milk Fat:
The fat globules arc appreciably subdivided (due to the vigorous agitation of milk at high temperatures).
(d) Free-Fat Formation:
Considerable free fat is produced (due to the rupturing of the fat globule membrane by the vigorous scraping action of the stirrer).
(e) Heat-Coagulation of Milk Proteins:
The serum proteins are coagulated by the action of heat, and casein is coagulated by the combined action of heat and concentration.
(f) Super-Saturated Solution of Lactose:
From a dilute solution in milk, lactose is present in khoa as a super-saturated solution.
(g) Partial Precipitation of Milk Salts:
A portion of the milk salts are precipitated by the action of heat.
(h) Increase in Iron Content:
From 2 to 4 ppm in milk, the iron content in khoa exceeds 100 ppm (due to the incorporation of additional quantities of iron from the pan-surface into the finished product by the vigorous scraping of the stirrer).
Market Quality of Khoa:
This may be subdivided into:
(a) Physical,
(b) Chemical, and
(c) Microbiological qualities.
(a) Physical Quality:
This includes:
(i) Colour and appearance;
(ii) Body and texture;
(iii) Flavour, and
(iv) Suitability for sweets.
These have been presented for cow and buffalo khoa in Table 11.5.
The physical quality of khoa will depend mainly on the type of milk used, viz., cow, and buffalo or mixed, and the method of manufacture followed. In general, market khoa, which is normally made from buffalo milk, should have a uniform whitish colour with perhaps a tinge of brown, a slightly oily or granular texture, and a rich nutty flavour which is generally associated with a mildly cooked and sweet taste.
Good quality khoa should be a compact mass of very small uniformly-sized granules, which shows no signs of fat and ‘or water leakage. Even if kept for over 24 hours, it should not taste gritty. The material, when fresh, should be able to produce a smooth, homogeneous paste on working—which indicates that it is ‘suitable’ for sweet-making.
(b) Chemical Quality:
It may be pointed out that khoa offered for sale should not contain any constituents foreign to milk and should not be adulterated with any type of starchy material, etc.
(c) Microbiological Quality:
This has yet to be prescribed. Although the milk is subjected to drastic heat-treatment during khoa- making, yet a large and varied microbial count has been reported in market samples of khoa by various workers.
Obviously these include the surviving spore-formers (which multiply during subsequent storage) and the contaminating micro-organisms (which gain entry during manufacture, handling, packaging and storage).
Yield and Overrun of Khoa:
(a) Yield:
The yield of khoa is rather variable and is influenced by:
(i) The type of khoa;
(ii) The type of milk;
(iii) The quality of milk;
(iv) The extent of dehydration (ratio of concentration of milk solids), and
(v) Losses in handling.
The type of khoa which contains a higher moisture content is certain to have a higher yield. The type of milk, viz., cow or buffalo, influences the yield by virtue of its total solids content; thus, buffalo milk with a higher total solids content gives a higher yield of khoa than cow milk with a lower total solids content.
The quality of milk refers to the total solids content; good or high quality milk refers to a high total solids content, which yields larger quantities of khoa as compared to poor or low quality milk with a low total solids content.
The extent of dehydration refers to percentage moisture, retained in the khoa; the more the dehydration, the lower the yield, and vice versa. Losses in handling which include accidental overflow, etc., obviously lower the yield of khoa. Normally the yield of khoa (with 28 per cent moisture) ranges from 17 to 19 per cent from cow milk and 21 to 23 per cent from buffalo milk.
(b) Overrun:
The overrun in khoa refers to the excess weight of khoa over the amount of total (milk) solids used in its production. The overrun is chiefly influenced by the moisture retained in khoa and the losses of milk solids. It is usually expressed as a percentage.
The formula for calculating overrun (OR) in khoa is:
Where,
K = weight of khoa (in kg.)
TS = weight of total solids in milk (in kg.).
Note:
In the market-place, the quality and purity of milk is judged by what is known as the ‘khoa test’. In performing this test, a predetermined amount (usually 1 kg) of milk is converted into khoa in the normal manner by the intending purchaser; and the price paid for milk to the supplier is in direct ratio to the amount of khoa obtained.
Packaging, Storage and Marketing of Khoa:
(a) Packaging:
Normally individual khoa-pats are not packaged. However, the following modern packaging materials and forms can be profitably used: Vegetable parchment paper wrappers; plastic (polythene) film bags/pouches, laminated (preferably aluminium coated) pouches; tin-plate cans, etc. The pack size usually varies from 0.5 to 1.0 kg., although packs smaller than 0.5 kg. are also available.
(b) Storage:
Khoa has a low keeping quality at room temperature, and storage at low temperatures (5-10°C) has been found to extend its shelf-life. Hence refrigerated storage is preferable.
(c) Marketing:
At present, khoa is generally marketed soon after production in an unpacked or crudely packed condition, depending on the distance of the market.
Keeping Quality of Khoa:
The keeping quality of khoa is chiefly influenced by the following factors:
(a) Temperature of storage;
(b) Quality of the raw material (milk);
(c) Initial moisture content;
(d) Sanitary conditions observed during manufacture;
(e) Type of package, and
(f) Method of packaging.
(a) Temperature of Storage:
The higher the storage temperature the lower the keeping quality, and vice versa. The average storage life of khoa (100 g. pack in a butter paper wrapper) made either from cow or buffalo milk at 37 ± 1°C, 23-24°C and 5-10°C was 7, 10 and 25 days respectively.
Khoa samples from mixed milks (500 g. lots packed while hot in laminated pouches and heat-sealed immediately) showed an average shelf-life at 37°C, 8 ± 1°C and —20°C of 5 days, 30 days and 75 days respectively.
(b) Quality of the Raw Material (Milk):
The quality of milk used for the production of khoa has a direct influence on the keeping quality of the finished product. Any developed acidity in milk lowers the keeping quality of khoa made from it. Hence only fresh, sweet milk, produced under sanitary conditions, should be used for khoa making.
(c) Initial Moisture Content:
The lower the initial moisture content of khoa, the higher the keeping quality, and vice versa.
(d) Sanitary Conditions Observed during Manufacture:
Since khoa is made in the open under the existing system of production, the sanitary conditions observed during manufacture will certainly play an important role in influencing its keeping quality. The better the sanitary conditions, the higher its storage life, and vice versa.
(e) Type of Package:
The type of package, as specified by the packing material, influences the keeping quality of khoa. Thus khoa samples (500 g. lots packed while hot in their respective pre-sterilized pouches) showed an average shelf-life at 8 ± 1°C of 14 clays and 30 days for parchment paper/polythene film and 4-ply aluminium-coated laminates, respectively.
(f) Method of Packaging:
This refers to whether khoa has been packed hot or cold, air-tight or loosely wrapped, etc. Hot packaging of khoa (in unsterilized cans) has been found to ensure a longer keeping quality than cold packaging. It has been reported that khoa (with an initial moisture content of 20-25 per cent) had an average shelf-life of 14-21 days when packed hot (80-90°C) and less than 7 days when packed cold (25-30°C).
Note:
Efforts to preserve khoa, i.e., to extend its keeping quality, have not been very successful so far. Heat-sterilization of canned khoa was found to adversely affect its sensory qualities and render the product unmarketable. The addition of potassium sorbate and butylated hydroxy anisole in permitted quantities did not extend the shelf-life of khoa.
Although irradiation of khoa with ultra-violet rays for 90 minutes was found to extend its storage life from 5 to 25 days, the irradiated product soon developed a disagreeable oxidized flavour so that it lost consumer acceptability. The addition of nicin was observed to extend the storage life of the canned product by more than one month at 10°C and by 2 and 3 weeks at 30 and 22°C, respectively.
Standardized khoa with an addition of potassium sorbate (in quantities greater than those tried earlier) showed a keeping quality of 10-11 days at 30°C and 40 days at 5°C; the addition of nicin (nisaplin) and anti-oxidants in permitted amounts did not increase its shelf-life.
Type of Spoilage in Khoa:
The spoilage in khoa at 37 ± 1°C and room temperatures (24-30°C) is characterized by a rancid flavour, while at low temperatures (5-10°C) it has a stale/sour flavour; at room and refrigerated temperatures, there is a mouldy growth on the surface.
Note:
Although during the manufacture of khoa, milk is subjected to drastic heat-treatment, the aerobic spore formers are known to survive such heat-treatment and may outnumber other types of micro-organisms, thereby suggesting that the survivors might have multiplied during subsequent storage. The possibility of contaminants gaining entry into these products during subsequent handling also cannot be ruled out.
Judging and Grading of Khoa:
Score Card:
A tentative score card of khoa is given in Table 11.6.
Procedure of Examination:
(i) Sampling:
Obtain a representative sample with the help of a sharp-bladed knife.
(ii) Sequence of Observations:
Note the sanitary condition of the package (if any). Before taking the sample, observe the surface of the khoa-pat and examine the uniformity of colour on the outside and inside. Observe the body and texture: note hardness/softness of body and sandiness/smoothness/coarseness/granularity/grittiness of texture; also note moisture and/or fat leakage.
Take a small piece from the khoa sample and taste on the tip of the tongue. Chew until melted and then roll the melted mass within the mouth. Note flavour (smell and taste). Expectorate the sample and note the after-taste.
(c) Requirements of High-Grade (Buffalo) Khoa:
This should have a uniform whitish (dull/light-greenish white) colour; soft body and smooth granular texture; and a rich, nutty flavour (which is generally associated with a slightly cooked smell and sweetish taste); and should be free from any off-flavours and surface dryness.
Uses of Khoa:
(i) As a base and filler for the preparation of a large number of indigenous milk-sweets such as gulabjamun, peda, barfi, kalakand, pantooa, etc.
(ii) For direct consumption with added sugar (optional).