Why doesn’t milk taste as good as it used to?

In addition to the humanistic factor that "memories are always beautiful", milk may indeed become "bland". In fact, foreign milk is also often bland.

Is this change progress? Is it regression? Or is it just helplessness?

Why is milk no longer fragrant and aromatic? What is the relationship between fragrance and nutrition? To answer these questions, let’s start with the “richness” and “fragrance” of milk.

01

The thickness and lightness are related to the content and form

The "rich" in "fragrant and thick" milk sometimes refers to the strong aroma, sometimes refers to the thick appearance of milk, and many people regard "a layer of milk skin appears after a while" as a symbol of "rich". We will talk about the "rich" in the sense of rich aroma later, here we will first talk about the "rich" in the sense of viscosity, which is the viscosity in scientific terms.

The viscosity of milk depends first on the solid content. The main solids in milk are fat, protein and lactose. The total solid content varies from one milk to another. Even from the same cow, the solid content of milk squeezed out under different circumstances may not be the same. The commercial milk we see, especially the same brand, has a very consistent composition, which is the result of adjusting the content during processing.

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The solid content in milk is closely related to the nutritional status of the cow. In addition, the fat content is also closely related to the feed. If the cow is "malnourished", the fat content of the milk will decrease. Therefore, the solid content in raw milk, that is, the "thickness", actually reflects the nutritional status of the cow to a certain extent.

The solid content of milk is closely related to the nutritional status of the cow.

Because the fat in milk is not good for health, people will "skim" it. Reducing the fat naturally reduces the solid content, so skim or low-fat milk will be "lighter".

In milk, fat exists in the form of individual "milk droplets". Fat and water are immiscible, and only the proteins adsorbed on the surface of the milk droplets can keep them in the water. However, since fat is lighter than water, these milk droplets tend to float to the top of the milk. When they float to the surface, they form a layer of "milk skin". Because it is rich in fat, it is "very fragrant". The floating speed is roughly proportional to the square of the particle size. That is, if the particle diameter doubles, the floating speed will quadruple.

Butter is a dairy product made from fresh or fermented cream or milk by churning.

Apart from being used to make snacks such as "Double Skin Milk", the stratification of milk is not a good thing. At the very least, it destroys the uniformity of the milk, and to a certain extent gives people a "stale" feeling. In order to avoid this situation, modern milk processing will undergo a "homogenization" process. This is to use external force to "beat down" the milk particles, usually reducing the particle diameter to about 1/10 of the original, and the stratification rate is roughly only 1/100 of the original. In addition to the solid content, the viscosity of milk is also related to the size of the milk droplets. Under the same solid content, the smaller the milk droplets, the lower the viscosity. Therefore, the homogenized milk will appear "lighter".

In addition, the viscosity of milk is also related to its acidity. Some bacteria in milk will break down fat and release fatty acids, while others will convert lactose into lactic acid, both of which will increase the acidity of milk. The increase in acidity will increase the interaction between proteins in milk, causing the milk to become sticky.

In general, the change in the "thickness" of milk is affected by different factors and needs to be analyzed in detail. It cannot be simply said that it is good or bad to feel that it has become "lighter".

02

Milky aroma, derived from the food of dairy cows

People often say that cows "eat grass and produce milk". The taste of milk is indeed closely related to what the cows eat. If analyzed by instruments, there are at least dozens of substances with "taste" in grass. The most important is a class of components chemically called "terpenes" (tiē). In addition, volatile substances such as aldehydes, esters, ketones, and hydrocarbons can also produce "smells". These substances contained in different plants are not the same. For example, "dicots" contain more terpene compounds than "gramineae".

When grass grows in the ground, its metabolism is normal and it does not release too many odorous substances. When the grass is cut, the lipoxygenase in the grass is quickly activated, oxidizing and decomposing the carotenoids and lipids in the plant, releasing a large amount of volatile substances with "smell". This is why you can smell a strong "grass smell" when you pass by a lawn that is being cut.

Do you smell the "grass" when looking at the picture?

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When cows eat grass, these odorous substances can be absorbed through the digestive system, through the blood and finally into the milk. In addition, the "aromatic substances" volatilized into the air can also be inhaled through the nose, enter the blood system through the lungs, and enter the milk more quickly.

It is not difficult to imagine that since those "good" flavors can enter the milk, then the "bad" flavors can also enter the milk. Therefore, in order to obtain the "fragrant" milk flavor, good feed and a clean environment are required.

Modern industrially produced milk is often fed standardized, carefully formulated feeds to cows. These feeds are usually designed to provide sufficient and balanced nutrition, so that cows can produce more milk and produce milk with more protein and fat. The taste of milk is not an important indicator. Bland milk taste is easier to standardize.

Standardized dairy cows.

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In order to increase the source of feed, a lot of dead grass, straw and their fermented products are used for milk feeding. As long as the combination is reasonable, dairy cows fed with these feeds can also produce qualified milk. However, in terms of "milk flavor", it is difficult to produce the "fragrant" in our childhood memories.

03

The taste of milk is really a mixture of various flavors.

As mentioned earlier, the taste of milk is closely related to the feed of the cows, which refers to the milk that has just been squeezed out. In real life, most people can only drink milk that has gone through "collection-transportation-processing-transportation-distribution". In fact, the taste of milk in the hands of consumers is very different from the milk that has just been squeezed out. Such milk brings together the influence of every step in the entire production and sales process, and it can really be described as "a mixture of flavors". The sources of foreign smell in milk can be divided into three categories: ABC.

A. Absorbed

The "odour" in the milking environment can not only be introduced into the milk through the cow's breathing, but can also enter the milk directly after it is squeezed out. If you leave a bowl of milk open in the refrigerator for half a day, you can roughly feel the change in taste. If you consider an environment with flies flying around and feces and urine everywhere, it is not difficult to imagine whether the squeezed milk will absorb some "condiments".

B. Bacteria

Milk itself is a very suitable "culture medium" for bacterial growth. Every step from milking to sterilization may introduce bacteria. Under refrigeration conditions, it only slows down their growth. Whenever the temperature is restored to high (even if it is only above 7 degrees Celsius), even for a short time, they will expand against the clock.

Different bacteria will produce different odors, the most common ones are "lees" and "rancid". The lees smell is generally caused by not timely and properly refrigerated, which will further transform into the "acidity" of milk. This acid is produced by miscellaneous bacteria, and is different from the lactic acid fermentation controlled by humans, and it is not a pleasant smell. Rancid smell is also caused by improper refrigeration and bacteria mainly acting on protein. Improper refrigeration for a long time will also cause milk to coagulate and stratify. When the number of bacteria in fresh milk is in the millions, a more obvious rancid smell will be produced.

C. Chemical reaction

Chemical reactions may come from drugs taken by sick cows, detergents used to clean containers, high acidity of water, iron or cobalt on containers, etc. If these factors are excluded, the quality of the milk itself will also affect the oxidation of fat, thus producing odor.

As mentioned above, the fat in milk is a particle wrapped in protein. If the protein membrane on the surface of the fat is broken, the fat will be released. These fats may be oxidized, releasing free fatty acids, producing the so-called "rancid taste".

There are many reasons that may cause this odor. Improper nutrition of dairy cows, such as insufficient protein content or calories in feed, will lead to insufficient protein content in milk, which makes fat particles easy to break. In addition, too long milking period, too long storage time of milked milk or too intense stirring will also increase the "rancid smell" in milk.

Oxidized milk may also produce a smell similar to that of old newspapers or metal. In addition to the influence of detergents, unclean containers and metal ions, this situation is mainly related to the low content of vitamin E in milk. Vitamin E is an antioxidant. If the feed lacks carotenoid vitamin E, the milk produced may be more susceptible to oxidation. In addition, factors such as the protein content, fiber and fat composition in the feed will also affect the vitamin E content. If other factors have been eliminated and the odor still exists, you can even add some vitamin E to the cow feed.

04

“Flavored milk” is more than just flavoring

Whether it is protein content, total bacteria count, or flavor, these indicators represent more than just themselves; they also reflect the health of the cows, their living environment, and the level of hygiene during milk processing.

People know that fresh milk with a high total bacterial count is not suitable for pasteurized milk. Many people think that the reason is that pasteurization is incomplete and the bacteria cannot be reduced to the qualified index; or that it is very expensive to reduce the total bacterial count to the qualified index. In fact, even if the bacteria in fresh milk differ by 10 times, it does not require much additional sterilization cost to reduce the bacterial count to "qualified".

However, fresh milk with a high total bacterial count is also accompanied by many peculiar smells, which cannot be removed by sterilization. If flavoring is not added, the "original taste" of inferior milk cannot be covered up. A major advantage of pasteurized milk is that it maintains the "original flavor" of milk. For "pure milk" that is not allowed to add any ingredients, the "original flavor" containing various peculiar smells is difficult to accept.

Many "flavored milks" are flavored by adding sugar and flavoring to cover up the odor. In this way, we have no way of knowing what the original milk tastes like. However, after "normal temperature milk" is processed by ultra-high temperature, the taste of the milk itself will change significantly. The original odor will not be so prominent.

Source: Guokr

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