The flavor of milk is the key to its popularity. Only when milk has been properly produced and processed can it be a pleasant and satisfying food. For this reason, an ability to judge and score milk is an asset to almost everyone involved in producing, processing or marketing milk.

Judging milk begins at the point of production – on the farm. A farmer needs to know when off flavors or conditions are present in his milk, so corrections can be made. Only in this way can quality control, which is the real purpose of all judging and scoring, be maintained.

Judging continues in the commercial dairy plant where the milk is processed. The milk is examined at various points in processing to check for any irregularity in the plant operation. And the finished product is examined by the plant’s quality-control specialists, who frequently compare their product with those of competitors.

How does a person learn how to judge and score milk? Training can come from experience in a dairy plant where a variety of milk flavors are found. Or it can come from work with prepared samples. In either case, a basic understanding of the problems involved in judging and a uniform application of judging procedures are very important.

Distinguishing tastes and odors
There are four primary taste sensations – sweet, sour, salt and bitter. Sugar produces the sensation of sweetness; lactic acid or tart apple the sour taste; common salt gives a sensation of saltiness; and quinine produces a bitter reaction. Likewise, there are four fundamental odor sensations – fragrant, sour or acidic, burnt and caprylic or goaty. Because flavor is a combination of taste and odor, the flavors encountered in milk may represent any of the above taste or odors, either alone or combined.

The taste buds of the tongue vary in their response to the four basic tastes. The sour taste may be noted along the sides of the tongue, salt along the side and tip, sweet generally at the tip and bitter at the base. The centers for determining odors are in the uppermost regions of the nasal cavity. For this reason, to get the maximum benefit of the odor part of milk flavor, note its odor by inhaling slowly and deeply before and after you put the sample in your mouth.

Factors affecting a judge or grader
Most people can develop a good sense of taste and smell, but because many flavors are present in minute concentrations, great skill is often necessary to detect them. In judging dairy products, in addition to developing a keen sense of taste and smell, you should keep yourself in the best of health. Illnesses, such as the common cold, numb the senses of taste and smell and may jeopardize your ability to distinguish one flavor from another.

Accuracy in identifying flavors is very important. You should be able to repeat your decision on the same or similar samples if your judgments are to be accepted. To do this, you should develop good taste “memory,” so you will recognize quickly any previously encountered flavor and its relative intensity.

Besides maintaining good health, you should consider certain personal practices. Smoking or using tobacco in any form may cause inconsistencies in judging. The flavor of tobacco may dull the senses of taste and smell, which can make it difficult to detect some of the most delicate taste and odors. Other possible “distractions” include strong or heavily scented soaps, shaving lotion, hair conditioners or perfumes.

Also avoid eating strong or highly seasoned foods, such as onions or chili, or using chewing gum just before judging dairy products. Eating a heavy meal just prior to judging dulls the senses of taste and smell. These senses are keenest when a person has eaten only lightly or is slightly hungry.

Judging room and facilities
The judging room or area should be clean, orderly, well lighted and ventilated and free from odors, noises or other distractions. The temperature should be approximately 72ºF. A waste container with a plastic bag or a sink with running water is necessary in judging. You should not swallow any of the sample. Instead, spit it out as soon as you have determined its taste and odor. Otherwise, you will soon dull your sense of taste and limit your capacity to judge many samples accurately.

A separate, disposable cup or container should be used to taste each sample. Glass or china containers may be used if rinsed between samples. A metal cup, unless stainless steel, might impart a metallic flavor. Some paper cups possess a taste or odor of paper. Paper towels are needed for wiping the hands and mouth.

Judging milk

Description and causes of off flavors
Flavors of milk may be caused, in general, by five factors:

1. health of the cow

2. feeds consumed by the cow

3. bacteriological action

4. chemical changes

5. absorption of foreign flavors after the milk is drawn

A number of off flavors, together with their probable causes, are listed below. By understanding their origin, you will have a better background for identifying and recognizing each of these particular flavors.

• Bitter
A bitter taste in fresh milk may be caused by strong feeds or weeds that may carry through into the milk or conditions present in milk from cows in late lactation. Bitter taste may also result from certain bacterial growth, but normally this will not occur unless the milk is held several days at low temperatures.

• Cooked
This flavor results from heating milk. It may appear when all or part of the milk has been heated too high or too long. Normally, the higher the heating temperature, the more intense the cooked flavor.

• Feed
The feed a cow eats may impart certain flavors to milk. Some stronger feeds will carry through more noticeably than others. Feed flavor can be minimized or eliminated by taking the cows off offending feeds at least four hours before milking. Certain feeds can be detected in milk if fed to the cow even 15 to 30 minutes before milking.

• Flat (watery)
The source of this uncommon flavor is difficult to determine. The flavor may be described as tasteless. The characteristic flavor or normal milk is lacking, but the milk has no off-flavor. Flat-flavored milk resembles normal milk that has been partially diluted with water, even though this may not have been done.

• Foreign

Any seriously objectionable flavor foreign to milk, such as fly spray, paint, oil, kerosene, creosote or a medicinal substance, will render the milk unpalatable or unfit for use. Such a flavor may either directly contaminate the milk or be absorbed.

• Garlic/Onion
The obnoxious weed flavor, imparted to milk when the cow eats garlic, onions or leeks, is not classified as one of the usual feed flavors described above. The garlic/onion flavor is recognized by the distinctive taste and odor suggestive of its name. It may actually be so objectionable as to render the milk undesirable for use.

• High-acid
Milk that has developed some acidity as a result of bacterial growth (generally Streptococcus lactis) will have a detectable acid flavor long before it may be classified as sour. Milk may have an acid flavor when only a small part of high acid milk is mixed with milk of lower acidity; yet the total acidity on the entire lot may be within normal range.

• Malty
This is not a common flavor but may be encountered in milk not properly cooled. Certain bacteria from improperly cleaned equipment, especially milking machines, may contaminate the milk and cause the objectionable malty flavor.

• Metallic
Metallic flavor is rough and puckery on the mouth and tongue. It is caused when milk comes into contact with corrodible metal, such as exposed copper on equipment or rusty milk cans or lids.

• Musty
This flavor is suggestive of musty or moldy hay. It may be absorbed directly by the milk but is more likely to come from feed or stagnant water consumed by the cow.

• Oxidized
This flavor, quite pungent in advanced stages, is definitely objectionable. The oxidized flavor embraces many other flavors which represent various stages of oxidation or partial changes in the fatty portion of milk. This is one of the most troublesome milk flavors and should be easily recognized. It develops when milk placed in a glass or plastic container is left in the sun for a short time or for a longer time under artificial light in a store cabinet.

• Rancid
This flavor, resembling the flavor of stale fat, is not encountered in its extreme form in fresh milk. A taste noticeable in fresh milk is sometimes referred to as “lipase” flavor, which is induced by the enzyme lipase. This enzyme causes a change in the composition of the milk fat. It is more noticeable either during winter, when cows are on dry feed, or during late lactation. Extreme agitation of warm raw milk in the presence of air, causing foaming, will result in a rancid type flavor within a few hours.

• Salty
Salty taste, which may be present in milk from cows in the late stages of lactation, is often characteristic of milk from cows infected with mastitis. It is not commonly found in herd milk or mixed milk received at a dairy plant.

• Unclean
The unclean flavor is seldom found except in pasteurized milk that has been stored too long or at a slightly high refrigerator temperature. Unclean flavor often accompanies the bitter flavor. It may be caused by growth of bacteria in milk or from contact of milk with decomposed material on improperly washed or sanitized equipment or utensils.

• Weedy
The weedy flavor is not included among the usual feed flavors. It generally has a bitter characteristic, varying with specific weeds of certain localities. It can be eliminated or minimized by keeping cows away from weed-infested pastures or by not offering feeds containing such weeds until after the cow is milked.

Examining the sample
Samples are best judged or scored with only number identification; knowing the brand or source of the sample may prejudice the judge. Before attempting to score milk samples for the first time, you should work with a trained judge or coach and learn to recognize and identify the various flavors you may encounter.

This is the usual procedure for identifying a flavor:

1. Put a warmed sample (60ºF) of milk into a glass or cup. If possible, before the sample is poured, quickly note the odor from the bottle or container; otherwise the odor may soon be lost. Also, immediately after pouring the sample, determine its odor.

2. Take a small sip, and with the mouth closed, not swallowing any of the milk, move your tongue moderately five or six times to assure that the rear of the tongue also comes into contact with the sample. At the same time, inhale and exhale slowly through the nose. This forces the aroma through the back of the nose, making it possible to note the aroma.

3. Spit out the sample quickly and identity the aftertaste. Hold the sample in your mouth no longer than about ten seconds. Holding it longer will dull your senses of taste and smell.

4. If necessary, repeat the procedures as a further check on your findings. Sometimes, it may be necessary to go on to the next sample, and come back later for a recheck . However, in order to avoid confusion and develop more confidence in your decision, do not recheck samples any more than is necessary.

It is advisable to allow a short interval of time between taking samples, especially after tasting the more harsh objectionable flavors. This interval will allow your saliva to refreshen your mouth. Sometimes rinsing your mouth with water helps, but this usually is not necessary.

Determining the flavor
Consumer acceptance of milk depends largely on a pleasing flavor. Before tasting a milk sample, you should note the odor or aroma. Smell the open container of milk, rather than the individual cup, since the greater volume in the bottle makes it easier to detect the odor. Frequently, odor alone is sufficient to classify milk properly. Tasting then only further substantiates the flavor found by the aroma. (Flavors, however, that are not volatile may be detected only by taste.)

Odor plays a very important part in quality determination at a dairy-receiving platform. Therefore, individual cans or transport tanks of milk are opened and the aroma is noted before the cans or tanks are emptied. Similarly, when milk is examined in a bulk tank at the farm, odor is quickly noted when the lid of the tank is first raised. Because flavors become more volatile at higher temperatures, warm samples carefully to about 60ºF prior to examination. A cold sample (below 45ºF) chills your mouth and makes it difficult for you to distinguish certain flavors.

The “ideal” natural flavor of milk should be firmly fixed in mind for comparison. The mental image will help in distinguishing between samples which show varying characteristics and types of flavor.  PD

—Excerpts from Farmers’ Bulletin No. 2259, U.S. Department of Agriculture