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Skimmed milk, partially skimmed and whole: the differences

Whole milk, partially skimmed or skimmed? The difference lies in the quantity of fatwhich influences taste, consistency and caloric contribution. Milk is in fact an emulsion consisting mainly of water in which small lipid droplets are dispersed: the industrial skimming separates the aqueous phase from the lipid one through centrifuges that exploit the different density of the components. Whole milk essentially has all its intact nutritional components and contains a percentage of fat equal to or greater than 3.5%. In partially skimmed milk, The fat portion is partly eliminatedfor which the fat content varies between 1.5 and 1.8%, while in the skimmed one the percentage of fat cannot exceed 0.5%. According to the guidelines of the Food and Nutrition Research Center (Crea) it is preferable to make a limited use of whole milk And prefer the partially or totally skimmed one to reduce the risk of cardiovascular problems, in the predisposed people. In any case, the overall calorie budget The crucial factor remains to keep the body weight stable: the milk lipids will not make us fat, if you do not go into exceptional in your daily requirement of fat.

Milk contains fat

Do we know the difference between the various types of milk that we encounter on supermarket shelves? Maybe yes, or maybe we just choose instinctively, between one cardboard and another, without thinking too much about it. Yet behind terms like “entire“,”partially skimmed“or”skimpy” There are small but important differences, which influence the composition of the milk and therefore the taste, the consistency and also the calorie intake. But first let’s take a step back to understand how the milk is made.

Different types of milk

From a chemical point of view, milk is a colloidal system, more precisely one emulsion. In fact we have one aqueous phase (consisting mainly of water, proteins, sugars and mineral salts) within which droplets are dispersed of oily phase (lipid portion mainly made up of triglycerides). What distinguishes whole milk from the skimmed and partially skimmed milk is precisely the quantity of these fats, which constitute the so -called cream.

The various types of milk

The Regulation (EC) n. 2597/97 defines the characteristics that distinguish the different types of milk:

  1. Whole milk: it must have a tenor of fatty material not lower al 3.50 % (m/m). To better understand this definition, taking 100 grams of whole milk as an example, at least 3.50 grams must be only fat. Some manufacturers can regulate the percentage of fatty material through the methods of addition or elimination of the cream, in this case we speak of Normalized whole milkwhich is distinguished from Non -normalized whole milk which is instead the one with its natural fat content, without any modification after milking.
  2. Partially skimmed milk: contains a lipid content between a minimum of 1.50 % (m/m) and a maximum of 1.80 % (m/m).
  3. Skimmed milk: its quantity of fat cannot exceed 0.50 % (m/m).

The whole milk has, for obvious reasons, a more consistency dense And creamy compared to the other two. Furthermore, it is even more opaque: having more fatty globules suspended in the liquid, these reflect the light more. On the contrary, skimmed or partially skimmed milk has a higher aqueous phase and therefore will be crossed by the light more easily.

How is the skimming of milk on an industrial level?

Before dealing with the topic, you have to make a physics review. The skimming of milk is used for eliminate part of the oily phase (or fat, or lipidic … in short, we understand that it can have different names). Water and fat and are inevitable between them, or they do not mix: however, the milk is an emulsion, which means that the aqueous and oily phase are mixed in a system temporarily stable.

By putting oil and water in the same glass, we will notice that the oil will not mix but will float. This is because, in general, fats are less dense water, which means that, with the same volume, they are less heavy. One of the physical methods to separate two components of a system that have different densities is the centrifugation, which in the industrial field takes place within special centrifugal separators.

Manual separator
Manual separator preserved in a Swedish museum.
Credits: Calle Eklund/V -Wolf, CC By -Ssa 3.0, via Wikimedia Commons

These are machinery with a large rotating drum that houses a series of conical housings for milk. When the drum starts to rotate (making about 6000-8000 rpm per minute) the milk is subject to one centrifugal force. The Second principle of dynamics It teaches us that any force applied to a body is calculated by multiplying the mass of the body to the acceleration that the body suffers. Since the aqueous phase is denser, and therefore heavier, the centrifugal acceleration acts on her with greater intensity, pushing her outwards and therefore crushing her against the walls. On the contrary, fat blood cells, Less dense and lighteraccumulate downwards. The oblique inclinations of the housings help to slide the watery phase towards the appropriate collection of collection and at the same time convey the lipid portion towards a second exit that is located on the opposite side.

Obviously, it is not a process that allows a complete separation, but efficient centrifuges manage to get skimmed milk with fat content lower than 0.1%.

What effect does it have on health?

Whole milk offers a greater quantity Of Liposoluble vitamins (A, d, and, k), while the content of other nutrients also remains the same in the skimmed variants.

The Creation (Food and Nutrition Research Center), in Guidelines for healthy nutritionsays that it is preferable to choose partially skimmed milk to the whole one, to limit the intake of saturated fats without renouncing a adequate contribution of football and proteins. Even beyond ocean, theAmerican Heart Association, He says that it is preferable to take milk with a low amount of saturated fats, which include not only triglycerides, but also cholesterol and free fatty acids.

These indications are mainly focused on people with cholesterol dysMetabolism or vascular problems (saturated fats can help increase theLDLthe notorious “bad cholesterol“). For those who are concerned with the maintenance of the line, it is important to remember that theaccumulation of fat mass mainly depends on the achievement of a caloric surplus. If the whole milk represents the main source of saturated fats and the caloric intake remains in balance with the needs, there are no risks of accumulation of body fat. For more in -depth indications, however, it is always better to rely on your nutritionist or a doctor.