Sensory Evaluation of Milk

Since milk is the raw material for all dairy products, its quality will ultimately influence the end products. Therefore, proper judging of milk, both raw and processed milks is very important and needs special care.

i. Desirable Attributes of Milk

Typically flavour of milk should be pleasantly sweet and possess neither a foretaste nor an aftertaste. The natural richness in milk is due to presence of milk fat and the sweetness due to milk sugar (lactose). The colour of cow milk is yellowish and of buffalo milk is white. The colour may vary depending on the extent of mixing the two milks. There shall be no fat globules/particles on the surface.

ii. Score Card for Milk

A 25-point score card has been recommended by American Dairy Science Association (ADSA) and 100 points score card by BIS (Table ).Full perfect score is normally awarded when there is no defect in milk, and zero score for an unsalable product.

Score Cards for Milk

iii. Order of Examination and Scoring

i) Sediment: It should be performed first. The kind, amount and size of sediment particles should be carefully observed by visual observation and scored against a chart of mental image.A 3-point scale may be employed occasionally. The presence of any sediment in the processed milk is serious and should receive a zero score. One possible scoring system using a sediment disc could be:

No sediment 3

< 0.02 mg/disc 2

0.025 mg/disc 1

> 0.02 mg/disc 0

ii) Containers and closure: It should be carefully observed. Now-a-days milk is invariably packaged in polyethylene sachets. Hence, the evaluator must see that the packaging is proper and there is no leakage/ pilferage from the pouches/ containers. The containers should be examined for the extent of fullness (specified amount), cleanliness and printing.

iii) Flavour: Milk should be properly tempered between 13 and 18oC, preferably at 15.5oC. Samples should be served in clean, odourless glass or plastic bottles.For each evaluator, about 50 ml sample should be provided. Immediately after removing the lid, the panelist should smell the milk and simultaneously observe for the presence of cream plug or partially churned fat globules. Then mix the sample properly and take a generous sip, not less than 10 ml of milk, roll it around the mouth and note the flavour and tectual sensation. Then expectorate the sample. Sometimes, the aftertaste may be enhanced by drawing a breath of fresh air very slowly through the nose. Slow agitation of milk leaves a thin film of milk on the inner surface of the bottle, which tends to evaporate thus readily giving off the odour present. The BIS has recommended that milk sample should be warmed to 45oC for evaluation of flavour and odour. Score of 30 has been alotted to body, which means consistency (watery/curdy) as per the BIS.

iv) Temperature: Raw milk as well as pasteurized milk should be stored at 7.2oC, but lower than 4.4oC is preferred. For pasteurized milk, if the temperature is above 7.2oC, the sample may be scored zero. Full two points may be given for a sample at or below 4.4oC.

v) Bacterial Count: The maximum permissible bacterial count in pasteurized milk in India is 30000/ml and coliform not more than 10/ml. A sample containing a higher count than this limit should get zero score out of five. The bacterial count, however, cannot be done on every sample of raw milk for judging purpose. Hence, it is recommended to perform the bacterial count test after a certain interval or in case of suspicion.

iv. Undesirable Attributes of Milk

The more common flavour defects of milk are: sour/high acid, flat, barny, feed, weed, bitter, cooked/burnt, rancid, oxidized, sunlight, cowy, salty, astringent and stale. The causes and method of simulation of these off flavour in milk for training purpose have been discussed in Unit 2.