Compilation of exam and interview questions and answers on Dairy Technology and Dairy Engineering .
Q.1. Explain the action of milk on metals.
Ans. Milk acts on certain metals, so that a small amount of the metal is dissolved in it. The metallic salts thus formed may give rise to a ‘metallic’ taste in the milk. Some salts act as catalysts, thus hastening the oxidation of fat and producing an oxidized flavour. These metals are said to taint milk.
The factors which influence the degree of action by milk on the metal are:
(i) Temperature of milk;
(ii) Period of contact;
(iii) Cleanliness and polish of metal;
(iv) Amount of free air in milk;
(v) Acidity of milk, etc.
Q.2. How to control corrosion in dairy equipment?
Ans. Corrosion cannot be entirely prevented in dairy equipment, but its rate can be controlled to a large extent.
To prevent corrosion of stainless steel surface:
(i) Keep the surface clean;
(ii) Permit surface to air-dry, whenever possible;
(iii) Use cleaners and sanitizers in the lowest concentration and for the shortest duration that will do the desired cleaning job.
Note:
(i) When the stainless steel surface is dry and exposed to the atmosphere, an invisible film of chromium oxide forms on it. This film protects it from corrosion. When the film breaks or wears away, the active metal gets exposed and corrodes more easily. This oxide film is self-forming when the stainless steel surface is dry and exposed to air.
(ii) Chlorine and its compounds are very corrosive. Equipment should be sanitized with chlorine solutions, preferably just before it is to be used, so as to avoid prolonged contact, and thus corrosion (pitting).
Q.3. How to test the quality of milk?
Ans. The various platform tests are discussed below:
1. Smell (Odour):
This furnishes an excellent indication of the organoleptic quality of milk. It can be ascertained very quickly (in just a few seconds). In making the test, the cover of each can is removed, inverted and raised to the nose. The odour/smell will be representative of that in the can.
The top of the milk in the can may simultaneously be noted for smell. By replacing the lid and shaking the can vigorously, the test may be repeated. An experienced milk grader with a ‘trained nose’ usually relies to a great extent in the acceptance/rejection of the intake milk on the odour test alone. The milk should be free from any off-flavours.
2. Appearance:
By regularly observing the milk in each can after the odour test has been made, any floating extraneous matter, off-colour, or partially churned milk may be noted. The milk should be normal in colour, free from churned fat globules and reasonably free from any floating extraneous material.
3. Temperature:
The temperature at which milk is delivered is often an indication of its quality. A daily check on the temperature of milk is helpful in grading the milk on the receiving platform. With practice, the grader can tell with a high degree of accuracy whether or not the milk is sufficiently cold by touching the side of the can. A temperature of 3°C or below is satisfactory.
4. Sediment:
The sediment test shows the visible foreign matter contained in the milk. It need not be made daily, but should be made sufficiently often to ensure a clean milk supply. For this purpose a reliable sediment tester (such as an off-the- bottom sediment tester), by which the work may be expedited, should be selected.
The intensity of discoloration and sediment on the pad will depend to some extent upon the manner in which the test is taken. Any method by which maximum sediment will be revealed should be considered satisfactory. A low sediment is desirable.
Note:
The sediment test is used as a check on the milk production and handling methods on the farm. A low sediment need not necessarily mean a low bacterial count in milk, although the reverse is often true. (A clean sediment disc does not indicate clean methods; it may be a pointer rather, to the milk having been filtered/strained on the farms).
5. Acidity:
It has already been pointed out that ‘natural’ or ‘apparent’ acidity of milk does not make the milk taste sour, nor does it affect the normal properties of milk or jeopardize its quality or its behaviour towards processing heat. However, ‘developed’ or ‘real’ acidity does adversely affect the quality of milk.
Note:
Determination of the Titrable Acidity of milk (which is equal to Natural Acidity plus Developed Acidity) for deciding acceptance/rejection of milk on the basis of an arbitrarily set limit cannot serve much useful purpose in India today, especially in view of the fact that the milk suppliers are freely adding neutralizers to milk to reduce its acidity.
Nevertheless, the ‘acidity test’ does have its proper place on the milk reception dock; and with the daily incoming milk it is always well to have a certain acidity above which milk should not be accepted. A modified form is known as the ‘rapid acidity test’.
6. Lactometer Reading:
The addition of water to milk results in the lowering of its lactometer reading. Hence this test is applied for detection of adulteration of milk with water. As it does not take much time, it is often used as a platform test in the milk collection/chilling centres in this country. However, this test has its drawbacks.
Q.4. What are flavoured milks. Explain its purpose and types.
Ans. Flavoured milks are milks to which some flavours have been added. When the ‘milk’ is used, the product should contain a milk fat percentage at least equal to the minimum legal requirement for market milk. But when the fat level is lower (1-2 per cent), the term ‘drink’ is used.
Purpose:
(i) To make milk more palatable to those who do not relish it as such;
(ii) To stimulate the sale of milk;
(iii) To put skim milk to profitable use.
Types:
The main types are:
(i) Chocolate milks/drinks;
(ii) Fruit flavoured milks/drinks;
(iii) Sterilized flavoured milks/drinks.
Q.5. Explain the meaning and characteristics of soft-curd milk.
Ans. Soft-curd milk is milk that forms a soft curd when coagulated with rennet or pepsin under standardized procedure. Soft-curd milk has a curd tension (CT) of less than 25 g.
Note:
The standardized procedure, such as the Hill Curd- Tension test consists in coagulating milk by means of a pepsin-calcium chloride solution and then measuring the resistance (in g.) which a special multi-bladed curd knife encounters in its passage through the coagulated milk.
Characteristics:
Soft-curd milk is characterized by:
(i) Low casein content;
(ii) Low calcium content.
Q.6. What are the merits and demerits of using metal churns.
Ans.
Merits:
(i) Cleaned easily with alkali detergents;
(ii) Steam sterilization possible without damage to the churn body;
(iii) Moisture and salt control are more accurate;
(iv) Intermittent use without deterioration possible;
(v) Much more sanitary.
Demerit:
Low heat-insulating capacity makes temperature control of churning rather difficult. Obviated by use of air-conditioned butter-making room and/or provision of chilled water spray during churning and working).
Q.7. Give the definition of processed cheese.
Ans. Processed cheese may be defined as a modified form of natural cheese prepared with the aid of heat, by comminuting and blending one or more lots of cheese, except certain types such as cream, cottage cheese, etc., with water, salt, colour and emulsifier into a homogeneous plastic mass (which is usually packed while hot).
According to the PFA Rules (1976), processed cheese refers to the product obtained by heating cheese with permitted emulsifiers and/or stabilizers, namely citric acid, sodium citrate, sodium salts of orthophosphoric acid and polyphosphoric acid, with or without added condiments, and acidifying agents, viz., vinegar, lactic acid, acetic acid, citric acid and phosphoric acid.
Processed cheese may contain no more than 4.0 per cent of anhydrous permitted emulsifiers and/or stabilizers, provided that the content of anhydrous inorganic salts in no case exceeds 3.0 per cent of the finished product. It should not contain more than 47.0 per cent moisture.
The milk fat content should not be less than 40.0 per cent of the dry matter. Processed cheese may contain 0.1 per cent sorbic acid or its sodium, potassium or calcium salts (calculated as sorbic acid) or 0.1 per cent of nicin, either singly or in combination.
Note:
Processed cheese food is cheese blended with legally limited amounts of dairy products such as cream, milk, skim milk, or whey (or their concentrates) and certain optional ingredients. Processed cheese spreads are made with cheese as a base but with the addition of optional ingredients, similar to those used in cheese foods, for desired flavour and body properties.
For processed cheese foods and spreads, higher heating temperatures such as 71-82°C (160-180°F), are normally required than in processed cheese, so as to more efficiently destroy heat resistant and putrefactive organisms. This improves the keeping quality of these perishable products. They are sometimes homogenized as well, as this treatment produces an extremely smooth consistency in the finished product.
Q.8. What are the merits of using processed cheese?
Ans. (i) Long keeping quality (so long as the package remains unopened);
(ii) Uniform flavour;
(iii) No waste in consumption;
(iv) Ease of Purchase;
(v) Sold in attractively packaged units, which are easily displayed;
(vi) Subject to few marketing losses (such as spoilage, shrink age, etc.);
(vii) Utilize unacceptable raw cheeses (which are sour, gassy etc.) in their production.
Q.9. Explain the early history and later developments of butter churn.
Ans. The modern butter churn is the culmination of a long period of development in churn construction. The main purpose of the churn is to agitate the cream.
This has been achieved over the years through the following basic designs:
(i) Swinging Churns:
The cream moves backwards and forwards in a horizontal plane. There are internal diaphragms in the churn to obstruct the flow of cream to some extent and thus to increase the intensity of agitation.
(ii) Rotating Churns:
These are either barrel or alfa churns. Barrel churns are of many types. Modern factory churns (wooden or metal) have been developed from rotating barrel churns.
(iii) Dash Churns:
In these, the cream-holding vessel is stationary, while the agitator or dasher (plunger, disc or rotating blade) is mobile.
Note:
The Indian indigenous churn is a dash churn.
Later Developments:
(i) Combined-Churn-and-Butter-Worker:
Early factory churns only churned the cream into butter; the working was done separately on circular/rectangular worker tables. The combined-churn-and- butter-worker was developed so that butter could be worked within the churn itself; the workers were installed on a trolley, which was pushed into the churn from either one of its ends or sides.
(ii) Roller-Less (Roll-Less) Churns:
In these wooden churns, the working was effected without the aid of rollers, which were found to be unsanitary. Vanes were fixed to vane churns, to help in the churning and the working of butter.
(iii) Modern Metal Churns:
These have been developed mainly in Denmark and the USA. The usual shapes are cylindrical, cubical or conical. The metal used for the product-contact surface is either stainless steel or aluminium alloy. The internal shape is so designed that working is effected by the rolling action of the butter.
Q.10. Explain the meaning and types of curd.
Ans. This is a soft, unripened cheese usually made from skim milk. It has a mildly acid flavour. It consists of small particles or flakes of curd which have a meaty consistency (when made from rennet curd). Creamed cottage cheese has cream mixed into it so that the finished product contains not less than 4 per cent fat. Both varieties are usually salted.
Types of Curd:
These are:
(a) Acid curd, in which the milk is coagulated by lactic acid developed by the action of a lactic starter;
(b) Rennet curd, in which milk is coagulated by the action of rennet in the presence of lactic acid, developed in turn by the action of lactic starter.
The character of cottage cheese resulting from these two types of curd is shown in Table 7.6.
Q.11. Describe the yield and keeping quality of cottage cheese.
Ans. The yield of cottage cheese before creaming depends essentially upon:
(i) The composition of milk;
(ii) Manufacturing losses; and
(iii) The moisture content of the cheese.
While the approximate yield of un-creamed cottage cheese is 15 per cent of milk that of creamed cottage cheese with (with 20 per cent fat in cream) and 4 per cent fat in the finished product is 18.3 per cent.
Keeping Quality:
The keeping quality of cottage cheese, whether uncreamed or creamed, is short even under refrigerated storage (5-10°C). Uncreamed cottage cheese may be preserved tor 90 days or longer by treezing or by brine storage. However, it will deteriorate in quality because freezing often leads to graininess and curd-shattering, particularly with rennet cheese.
Q. 12. What do you mean by curing cheese:
Ans. The curing/ripening/souring/maturing of cheese refers to the storage of cheese for at least 2 to 3 months at a given low temperature (0-16°C), during which its physical, chemical and bacteriological properties are profoundly changed, resulting in the development of a characteristic flavour, body and texture.
The term ‘green cheese’ is usually applied to hard-pressed cheese in the early stages of ripening before the characteristic flavour, body and texture of ripened cheese have developed.
Ripening agents influence the rate, extent and nature of ripening in cheese and include micro-organisms (chiefly bacteria and moulds) and enzymes, including pepsin.
Q.13. Explain the changes that take place during curing (cheddar).
Ans. (a) Physico-Chemical:
(i) Flavour:
From a mildly acid taste and aroma (no real cheese flavour) in green cheese to the development of the characteristic flavour of ripened cheese. The latter is really a blend of several odours and tastes, such as diacetyl in mild cheese, to traces of odours of butyric and caproic acid, esters of alcohol, salts of propionic and acetic acids in well-aged cheese and pungent odours of compounds of ammonia and sometimes hydrogen sulfide in very old cheese.
(ii) Body:
The cheese becomes slightly harder, due to loss of moisture. There is also a gradual change from the rubbery body in green cheese to a mellow and waxy body in ripened cheese.
(iii) Texture:
Cured cheese tends to acquire a fairly close to close texture.
(iv) Chemical:
The chief chemical changes which occur during the curing of cheddar cheese are: fermentation of lactose to lactic acid and small amounts of acetic acid, propionic acid and carbon dioxide; proteolysis; and a slight fat breakdown.
The most obvious chemical changes are the breakdown of the proteins and the newly created solubility of about 25 per cent of total proteins in cured cheddar cheese. In addition to fat breakdown, the ammonia produced by moulds and certain bacteria may have considerable effect on the pH of the cheese and so assist in the growth of other types of bacteria.
An increase in acidity and decrease in pH takes place for the first few days. The pH is lowest in cheese on about the third or fourth day after pressing, and is normally 5.10 to 5.05. It then decreases slowly and steadily during the curing period, as shown in Table 7.4.
(b) Microbiological Changes:
All cheeses contain, or should contain, predominantly lactic streptococci during manufacture and the early stages of curing. Cheeses of the cheddar type which are low in moisture and close in texture sustain a steady changeover from streptococci to lactobacilli, some of which contribute to the flavour. Other types are of course present and the higher the proportion of miscellaneous types, the quicker is the curing and the greater the possibility of off-flavours.
Q.14. What are the precautions that are to be taken during curing cheese?
Ans. (a) Selection of Cheese:
Only the right quality of cheese should be selected for curing; a cheese which is either too sweet or too acid should be avoided. There should be no damage to the rind.
(b) Supervision:
The cheese should be examined periodically for flavour, body and texture, finish, etc. The walls, floors, shelves/ racks, etc., of the curing rooms should be regularly inspected and kept in sanitary condition. That the temperature and humidity in the curing rooms is correct should be checked, and then be maintained.
Q.15. Explain the factors that cause shrinkage in cheese:
Ans. This refers to the loss in weight of cheese during curing/storage. Although a slight shrinkage is natural, excessive shrinkage should be prevented. Shrinkage is caused mainly by ‘loss of moisture’.
The factors causing shrinkage, i.e., loss of moisture, in cheese, are:
(i) Temperature of Curing/Storage:
The higher the temperature, the higher the shrinkage, and vice versa.
(ii) Relative Humidity of Curing/Storage Room:
The higher the humidity, the lower the shrinkage, and vice versa.
(iii) Size (and Shape) of Cheese:
The larger the size, the lower the shrinkage, and vice versa.
(iv) Moisture Content of Cheese:
The higher the moisture content, the higher the shrinkage, and vice versa.
(v) Paraffining of Cheese:
Paraffined cheese undergoes less shrinkage, than non-paraffined cheese.
Note:
The other cause of shrinkage is loss of fat.
Q.16. What are the methods used for measuring curing progress?
Ans. These are:
(a) Judging:
This is the most practical method. The cheese is examined organoleptically at regular intervals for changes in flavour, body, texture, colour and appearance.
(b) Physico-Chemical and Microbial Changes:
These include:
(i) Rheological properties, such as hardness/firmness, elasticity, plasticity, etc.;
(ii) The freezing point;
(iii) Enzyme content;
(iv) Microbial flora and content;
(v) Moisture, lactose, fat-acidity, pH, volatile-acidity contents; oxidation-reduction potential, salt-distribution, etc.
(c) Protein Changes:
Protein degradation measurements have been used most systematically and extensively in studying the ripening of cheese.
The rate of ripening is measured by determination of the ‘ripening index’ as follows:
Q.17. What is the role and importance of lactic acid in cheese making and curing?
Ans. Lactic acid plays an important role in the manufacture and curing of cheese because of the following effects:
(i) Helps in curdling milk with rennet;
(ii) Helps in expulsion of whey;
(iii) Helps in the fusion of curd particles;
(iv) Exerts protective action against putrefactive bacteria;
(v) Favours proteolytic action of rennet extract during curing.
Judging of milk refers to the act of evaluating its ‘Eating Quality’ on the basis of various attributes. Grading refers to its classification into different grades. The ‘Eating Quality’ of a dairy product is determined by organoleptic/sensory tests, which include all the five senses of sight, smell, taste, touch and sound. Of these, taste and smell are the most important in judging and grading.
Importance:
The consumer acceptability of a dairy product is determined primarily by its eating quality, i.e., by the sensations of smell, taste, feel, etc., which the consumer experiences when the product is tasted or consumed. It is well known that dairy products cannot be of a higher quality than the raw material from which they are made.
Hence, milk producers should have definite knowledge as to what constitutes desirable and undesirable flavours in milk, as well as the factors causing them; only then will they be in a position to produce milk that would make high- scoring finished products.
A processor of milk (and manufacturer of dairy products) should have the ability to discriminate against certain objectionable flavours and manufacturing defects; and to recognize desirable flavours and make-up characteristics, since these will enable him to make a product of good consumer acceptability.
The consumer should have adequate knowledge of desirable and undesirable flavours in milk and milk products, as these will enable him to purchase the same wisely and get his money’s worth.
Q.18. Describe the procedure for examining the quality of market milk (and scoring).
Ans. (a) Sampling:
Secure a representative sample aseptically by the standard procedure for bacterial count determination.
(b) Sequence of Observations:
(i) Sediment:
The sediment discs should be compared with standard charts for scoring. (However, sediment scoring of packaged milk is no longer done in standard contests.)
(ii) Closure (Cap):
After having scored for sediment, the closure should be carefully observed and scored.
(iii) Container:
The glass container is examined next for fullness, cleanliness and freedom from cracks and chips, particularly about the pouring lip. The paper container is examined for cleanliness, freedom from leakage, smoothness and the adherence of a coating to its surface. Correct tillage can be determined only by actual measurement of the volume of milk in a graduated cylinder.
(iv) Flavour (Smell and Taste):
This is scored only after the above items have been considered. The temperature of the milk should be around 16-21°C (60-70°F). The milk should be well- mixed before it is sampled in a small clean drinking-glass/beaker/ paper-cup.
As soon as the milk sample has been taken, sip (but do not swallow) a sufficient amount of it (5 to 10 ml.) to yield a normal taste reaction and yet one sufficiently small to permit its easy manipulation in the mouth. Roll it about the mouth, note the flavour and sensation, and then expectorate it. Note the aftertaste as well. By placing the nose directly over the milk when it has been shaken, any off-smell may be detected.
Q.19. Describe the requirements of high-grade market milk:
Ans. (i) The container should be neat and clean and contain the full volume of milk represented. The milk in the bottle should be protected from contamination by a well-made, well-seated, waterproof cap, which protects the pouring lip fully.
The bottle itself should be bright, shining, free from dirt, dust, etc.; it should not be cracked or chipped, particularly on the pouring lip. Paper/plastic containers should be clean and fresh with no leakage, pronounced bulging, etc.
(ii) The milk should be delivered at 10°C or below.
(iii) It should have the least amount of sediment.
(iv) It should have a low bacterial count. (High quality milk is low in bacteria, but low-bacteria milk may not always have the best flavour.)
(v) The flavour of the milk should be pleasantly sweet, and should have neither a foretaste nor an aftertaste, other than what is imparted by its natural richness.
Q.20. Classify the grades of manufacturing milk.
Ans. Although there should be a single minimum standard of quality for all milk, whether it is to be used directly as fluid milk or for the manufacture of various products, this is not so in practice.
The following classification may be used:
(a) Grade I:
Milk with a clear pleasant flavour, MBR time over 5½ hours and practically no sediment on sediment disc. (Tolerance for- slightly feed, flat or salty off-flavours.)
(b) Grade II:
Milk having off-flavours such as- definitely feed, flat or salty; slightly barny, bitter, foreign, malty, metallic, musty, oxidized or rancid; or very slightly weedy; MBR time between 2½ and 5½ hours; or milk which shows a medium amount of sediment.
(c) Grade III:
Milk having off-flavours such as- definitely barny, bitter, foreign, malty, metallic, musty, oxidized or rancid; or slightly high-acid; MBR time between 20 minutes and 2h hours; or definitely high in sediment.
(d) Reject or No Grade:
Milk with markedly high-acid, rancid, weedy, or foreign flavours; MBR time of less than 20 minutes and containing an extremely high amount of sediment or any noxious foreign matter.
Note:
The use to which each grade of milk is put will depend upon public health regulations concerning conditions of production and upon the specific character of the product.
In general, the following categorization may be made:
Grade I = Market milk, Sterilized milk, Evaporated milk, Sweetened condensed milk, Milk powder (whole or skim); Infant food, Cheese, etc.
Grade II = Butter, Ice cream, Flavoured milks, Fermented milks, Khoa, Chhana/Paneer, Butteroil, Ghee, etc.
Grade III = Ghee, Casein, etc.
Q.21. What is the procedure for neutralization of cream?
Ans. The procedure for correct neutralization is:
(a) Adoption of a definite standard of churning acidity;
(b) Testing correctly for acidity;
(c) Correct amount of neutralizer to be added;
(d) Adding neutralizer to cream by the correct method;
(e) Checking results by re-testing acidity.
(a) Adoption of a Definite Standard for Churning Acidity:
(i) Butter for Long Storage:
Cream acidity should be reduced to 0.06-0.08 per cent before churning for optimum results.
(ii) Butter for Early Consumption:
Cream acidity should be reduced to 0.25-0.30 per cent before churning.
Note:
(i) As acidity in cream is contained chiefly in the serum portion, cream-serum acidity is more reliable than cream acidity.
(ii) The richer the cream, the higher the cream-serum acidity.
The relation between cream acidity (CA) and cream- serum acidity (CSA) is calculated by the following formula:
(b) Testing Correctly for Acidity:
The procedure is:
(i) Take a sample of cream after thorough mixing.
(ii) Heat cream to boiling point for 1 minute before testing for acidity. (This method is satisfactory for sweet cream only.)
(iii) First partially neutralize acid cream with a known amount of standard alkali, then treat as above. (Recommended method for acid cream.)
(iv) Determine lactic acidity of cream by titration of a fixed weight (10 g.) with a standard alkali (N/9 sodium hydroxide solution), using phenolphthalein as an indicator.
Note:
The dissolved carbon dioxide in cream acts as carbonic acid and increases the titratable acidity value because it reacts with sodium hydroxide; but it does not utilize any of the bicarbonate neutralizer added, thereby over-neutralizing the cream.
(c) Correct Amount of Neutralizer to be Added:
The considerations are:
(i) The quantity of neutralizer to be added to a vat of cream varies with the acidity of cream, the final acidity desired in pasteurized cream and with the neutralizer compound used.
(ii) It is necessary, first, to calculate the quantity of lactic acid to be neutralized per 100 kg cream. Then the amount of neutralizer required must be calculated.
(iii) There are two groups of neutralizers available for use, viz., lime (calcium hydroxide and magnesium hydroxide) and soda (caustic soda, sodium carbonate, sodium bicarbonate and sodium sesquicarbonate).
The following equations represent the neutralizing actions:
(iv) The requirements, both theoretical and practical, of two selected neutralizers are given in Table 3.7.
(v) The comparative merits and demerits of lime and soda neutralizes are shown in Table 3.8.
(d) Correct Procedure for Adding Neutralizer to Cream:
(i) The neutralizer should never be dry when added, but should be dissolved/suspended in clean, potable water and properly diluted (mixed with 10-15 times its weight in water). It should be distributed quickly and uniformly in the cream and mixed thoroughly by stirring vigorously.
(ii) The temperature of cream when adding the neutralizer should preferably be 29-32°C (85-90°F). The stirring should be continued for 5-10 minutes after adding the neutralizer; then the cream should be pasteurized.
(e) Checking Results by Re-Testing Acidity:
The cream acidity should now be determined to check whether it has been correctly neutralized.
Role of Carbon Dioxide in Neutralization of Cream with Sodium Bicarbonate:
Fresh cream always contains some dissolved carbon dioxide; acid cream contains more of it. The carbon dioxide (as carbonic acid) reacts with sodium hydroxide during titration and shows a higher acidity test. But the carbon dioxide does not react with sodium bicarbonate neutralizer and consequently over-neutralization results.
Double Neutralization with Lime and Soda:
The following sequence is recommended:
(i) First use lime neutralizer to bring the cream acidity down to 0.3-0.4 per cent.
(ii) Next use soda neutralizer to bring the cream acidity down to the desired level.
Note:
The objects of double neutralization are:
(i) To avoid the intense effect on flavour of a large amount of any one neutralizer with high-acid cream;
(ii) To avoid production of excessive carbon dioxide by the use of sodium bicarbonate with high-acid cream.
Q.22. Explain the procedure of examining butter.
Ans. Some Requirements for Judging:
(i) Condition of Judging Room:
The butter judging room should be clean and well-ventilated. The temperature should be at about 16°C (60°F). There should be no foreign odours either within the room or nearby. There should be plenty of light for inspection of colour.
(ii) Tempering of Butter:
Cold butter should be kept in the judging room sufficiently in advance of the judging so as to bring it to the correct temperature (16°C). This is called ‘tempering’ the butter.
Sampling:
The sample plug is taken by a butter trier which is inserted in the block of butter diagonally near the centre, turned one-half of the way and then withdrawn.
Sequence of Observations:
Immediately after withdrawing the plug, pass the trier slowly under the nose, inhale through the nose very slowly and notice the odour or aroma present. Then examine the colour for uniformity throughout. Next, examine the body and texture by pressing the ball of the thumb against the sides of the plug until it shows a break. Observe the presence or absence of free moisture or ‘beads’ of water and their clarity, and also the nature of the break.
Then break off about 2-3 cm. at the end of the plug and put it into the mouth. Chew it until melted, then roll the melted butter about in the mouth until it reaches body temperature. Meanwhile examine for undissolved salt and the manner in which butter melts. Notice also the various sensations of taste and smell. Expectorate the sample and observe the after-taste.
Note:
Rinse the mouth frequently with one per cent lukewarm saline water, preferably after judging each sample.
Requirements of High Grade Butter:
The package should be neat, clean and tidy in appearance, and should have a good finish. The salt should have dissolved properly. The colour should be uniform throughout. The body should be firm and waxy, and its texture close-knit. The desired flavour is mildly sweet, clean and pleasant.
Flavour Defects that cause Butter to be Classified as ‘No Grade’:
These are:
(a) Chemical:
Chlorine smell (due to chlorine left inadvertently in butter churn, etc.).
(b) Foreign:
Petrol, kerosene, fly spray, etc. (Cream or butter in an open vessel absorbs such flavours readily.)
(c) Paint or Varnish:
Absorption of paint or varnish smells (due to exposure or contact of the same with butter).
(d) Surface Taint or Limburger:
A very serious flavour defect, resembling limburger cheese. (Caused by activity of proteolytic bacteria in the presence of low-acid-and-salt in butter.)
Q.23. What are the uses of butter?
Ans. (i) Direct consumption with bread;
(ii) In the preparation of sauces;
(iii) As a cooking medium;
(iv) In the baking and confectionary industries;
(v) In the manufacture of ice cream, butter oil and ghee (India).
Q.24. How to manufacture sterilized or canned cream?
Ans. The various steps are:
(i) Fresh, sweet cream is first standardized to 20 per cent fat;
(ii) Pre-heated to 80°C (176°F), without holding;
(iii) Double-homogenized at 80°C (176°F), using 2,500-3,000 psi in the first stage and 500 psi in the second stage;
(iv) Immediately cooled to 16°C (60°F), preferably over a surface cooler using brine;
(v) Filled into tin-cans (or bottles) and immediately sealed;
(vi) Sterilized in retorts (as for Evaporated Milk) employing 15 minutes for coming-up, 12-15 minutes for holding at 118°C (244°F), and 15 minutes for cooling to room temperature.
(b) Plastic Cream:
This is obtained by:
(i) Re-separating normal cream (30-40 per cent) in a normal cream separator, or
(ii) Separating milk in an especially designed plastic cream separator.
Note:
In both the above cases, the initial product is pasteurized at about 71-77°C (160-170°F) for 15 minutes and cooled to 60-66°C (140-150°F) before separation.
(c) Frozen Cream:
Objects:
(i) To improve the keeping quality of cream during transportation over long distances;
(ii) To store surplus cream for use during shortage. Mainly used by ice cream manufacturers who add sucrose (10-15 per cent by weight) to cream before freezing to prevent ‘oiling-off’ after thawing?
Method of Manufacture:
(i) Separate and standardize cream to 40-50 per cent fat;
(ii) Pasteurize at 77°C (170°F) for 15 minutes;
(iii) Cool to below 4°C (40°F) and fill into paper/plastic containers or tin-cans and seal well;
(iv) Freeze quickly and store at — 12°C (10°F) or below.
Effects of Freezing on Cream:
The membranes enclosing the fat globules are partially ruptured by ice crystals. Frozen cream tends to ‘oil-off’ on thawing, especially at higher temperatures. This ‘oiling-off’ impairs the whipping property of the product.
(d) Clotted Cream:
This it prepared by heating cream to 77- 88°C (170-190°F) in shallow pans and then allowing it to cool slowly. The surface layer consists of clotted cream, which is skimmed off and strained.
(e) Sour Cream:
This is a heavy-bodied ripened cream of high acidity (0.6 per cent lactic acid), clean flavour and smooth texture made by inoculating sweet, pasteurized and homogenized cream with a culture of lactic acid and allowing fermentation to proceed until these desired qualities are obtained.
(f) Synthetic Cream:
This is a mixture of flour, egg-yolk, sugar, water and a vegetable fat usually groundnut oil.
Q.25. How to examine the quality of table cream?
Ans. Sequence of Observations:
Carefully transfer bottle/container from refrigerator/cold room (5-10°C/40-50°F) to the laboratory in a vertical position, avoiding undue agitation.
Then examine in the following order:
(i) Take note of serum separation;
(ii) Take note of sediment at the bottom of the bottle;
(iii) Observe container and closure for fullness, cleanliness and general appearance;
(iv) Take note of cream plug, if any;
(v) Secure representative sample for bacterial count (aseptically by standard procedures), to be used later for other tests;
(vi) Temper cream to 10°C (50°F) and determine viscosity;
(vii) Take about 20 ml cream in a 100 ml beaker. Warm it to 15-21°C (60-70°F) and note the smell. Then put some cream in the mouth and note the taste;
(viii) Determine percentage of titratable acidity and fat;
(ix) Test for defects such as oiling-off, feathering in coffee, etc.
Requirements of High-Grade Table Cream:
High quality table cream should have a clean, sweet, pleasant, nutty flavour. The body should be smooth, uniform and reasonably viscous for the percentage of fat present. The physical appearance should be good.
Manufacturing Cream:
Requirements for High Grade Product:
Sweet cream, which is to be processed or manufactured into other dairy products, should be of a high quality. The cream should have a low acidity and clean flavour, should be fresh and delivered to the dairy factory in a clean, sanitary container adequately protected from contamination and against heat in transit.
Q.26. Explain the uses of cream.
Ans. (i) For direct consumption as table/coffee/whipping creams;
(ii) In the preparation of special dishes;
(iii) In the production of plastic, frozen and cultured (sour) creams;
(iv) In the manufacture of butter, cream, cheese, ice cream, butter-oil and ghee (India);
(v) For creaming cottage cheese.
Q.27. What do you mean by the heat stability of milk?
Ans. The heat-stability of milk is of tremendous importance in the successful processing of milk and the manufacture of most dairy products. The application of heat to milk becomes necessary for destruction of spore-resistant micro-organisms and the preservation of the most desirable product characteristics. However, milk should not coagulate during heating. Heat-coagulation of milk is caused chiefly by de-stabilization of the milk-proteins.
Heat-stability of milk may be defined in terms of the time required to induce coagulation at a given temperature, such as 115°C/239°F. Alternatively, the term ‘heat-stability of evaporated milk’ refers to the relative resistance of the milk to coagulation in the sterilizer.
Q.28. Explain the mechanism of heat-coagulation of milk.
Ans. The coagulation of milk revolves around the coagulation of milk proteins. Milk proteins are composed of several proteins, notably casein (containing α, β, γ fractions) which represents 82 per cent and whey proteins (containing β-lactoglobulin, α-lactalbumin, immuno-globulins etc.) which represent 18 per cent of the total quantity.
Casein exists in milk as complex colloidal particles or miscelles containing calcium, magnesium, phosphate and citrate in addition to casein proteins. This system is generally referred to as the calcium-caseinate-phosphate complex.
The casein miscelles range in diameter from 30 to 300 mµ, are stabilized by an electric charge and are in constant kinetic motion. As soon as the casein particles in milk join together to form large aggregates, coagulation takes place.
Q.29. What are the factors influencing the heat-stability of milk?
Ans. The chief factors are:
(i) Acidity and pH of Milk:
The higher the acidity (and lower the pH), the lower the heat-stability, and vice versa. Addition of acid to milk, either by bacterial action or chemical means, results in an increase of ionic calcium, which in turn disturbs the salt balance and lowers the heat-stability of milk.
(ii) Concentration of Total Solids:
The higher the total solids concentration, the lower the heat-stability, and vice versa Increase in concentration causes a marked shift in the salt equilibrium, increase in destabilizing ions and reduction in pH.
(iii) Concentration of Salts and Ions:
Any increase in concentration of either the numerator or denominator of the ionic ratio:
(Calcium + Magnesium) / (citrate + phosphate)
It disturbs the salt-balance, resulting in lowered heat-stability.
(iv) Pre-Heating/Forewarming of Milk:
The temperature-time and method of pre-heating/forewarming of milk affects the heat-stability. However, the mechanism by which this effect takes place is not yet completely understood. (The modern trend is towards high-temperature and short-time heating).
(v) Homogenization:
Homogenization of milk tends to slightly lower its heat-stability, which is affected by the pressure used; the greater the homogenization pressure, the greater the reduction in heat-stability.
Q.30. How to control the heat-stability of milk?
Ans. This may be done by either of the following procedures:
(i) Forewarming/Pre-Heating of Whole Milk:
The modern trend of high-temperature-short-time pre-heating/forewarming of milk appears to give much greater heat-stability than the low-temperature- long-time method.
(ii) Heat-Treatment after Condensing Evaporation:
Heating the milk- concentrate to temperatures above the boiling point increases heat- stability. (However, it is advisable to determine the effect of such treatment on test samples before attempting to heat-stabilize the entire lot.)
(iii) Addition of Chemical Stabilizer:
This is the basis of the Pilot Sterilization Test. In most cases the heat-stability is restored by addition of citrate or phosphate. However, some milks may require the addition of calcium-ions (as calcium chloride).
Note:
The use of sodium bicarbonate as a casein stabilizer has long been discontinued because of the following objections- it tends to darken the colour and jeopardize the flavour of evaporated milk; its release of carbon dioxide under sterilization heat causes excessive bulging of the cans; and when used in large amounts, it may lower rather than raise the heat- coagulation points—the latter being desired.
(iv) Mineral-Ion-Exchange Treatment:
By exchange of calcium and magnesium with sodium in a portion of milk, its heat-stability increases, leading to decrease of curdling tendencies in the sterilizer. (However, from a nutritional point of view, this procedure may raise objections.)
Q.31. Describe the factors affecting the rate of cheese curing:
Ans. (a) Time:
The rate of curing is higher in the earlier stages than in the later ones. (During the first 3 months, two-thirds of the total water-soluble protein-degradation compounds are formed.)
(b) Temperature:
The higher the temperature, the higher the rate of curing, and vice versa.
(c) Moisture Content of Cheese:
The higher the moisture content, the higher the rate of curing, and vice versa.
(d) Size of Cheese:
The larger the size, the higher the rate of curing, and vice versa.
(e) Salt Content of Cheese:
The greater the salt content, the lower the rate of curing, and vice versa.
(f) Amount of Rennet Added for Coagulation of Milk:
The greater the amount of rennet added, the higher the rate of curing, and vice versa.