Principles and techniques of steam milk 0
Steam Milk

The Science Behind Perfect Steamed Milk

While Espresso is the heart of a Cappuccino or Latte, although it does not account for more than 1/3 of the volume, milk and milk foam occupy the rest of the cup. However, most of the Barista we spend a lot of knowledge about the process of extracting coffee, but do not have much similar information on how to properly milk (steaming).  So, there are several issues that The Tenshi Coffee will tackle together on this topic, which are the principles of proper steam milk, some considerations when using skim milk, and finally, other points such as milk for Cappuccino and Latte. This article is for reference only, with your professionalism, please share your opinion!  

The chemical composition of milk

Using a little bit of chemical knowledge, youll have a better insight into whipping – Steam Milk before you start researching the “submerged part” of a vast body of knowledge related to milk foam.
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Think of milk this way: Cows milk is a nutritional supplement for young calves. It is full of all the essential nutrients a cow needs, namely water, sugar, protein, fat, and minerals. In which water accounts for the majority of milk, about 87%. The second most common compound in milk is sugar, accounting for about 4.8%. (Cows milk has a special sugar called lactose – thats why fresh juice has a sweet, sour taste when fermented (bacteria in milk convert lactose into lactic acid). Although the skim milk ad says that they have separated 1 – 2% of the free fat in the milk, the fact is, for pure natural fluid, the average fat content is about 3.9%. In comparison, Milk Protein accounts for about 3.4% of the total volume of whole milk. We often refer to the protein in milk as a foam formation and stabilizer. However, fat also plays an equally important role (will be discussed later). The remaining in milk, mainly different minerals (0.8%), such as Ca, Mg. These minerals have a reasonably limited influence on the taste of milk in general and dairy in particular.  

Principle of milking – Steam milk (Steaming)

When you milk, you do two things at once: create a foam by introducing air into the milk and heating the milk. The milk manipulation for Cappuccino and Latte will be presented in more detail at the end of the article). When the Steam is compressed by pressure through the holes in the steam head, they will create a stir on the milk surface with the “creaking” sound; the surface air is quickly fed into the milk by this movement. If the head is completely submerged in liquid, the surface of the milk lacks stirring. The hot Steam will still heat the milk, but there will be no air coming in – which means no bubbles. While Steam puts microbubbles into the milk to inflate this structure, Steam also heats the liquid (its time to go back to the protein component mentioned earlier). In cold milk, milk proteins exist either in the form of folded molecular blocks (tertiary structure) or by multiple protein molecules linked together (fourth-order). Then, as the milk warms, the proteins begin to expand to form a “keep air” texture.  

Temperature and milk protein

One of the most popular proteins in milk is Casein, which accounts for about 80% of the milk protein component, hundreds of thousands of molecules of this protein linked together to form casein-micelles spheres that create the milky white color of milk (as on Infographic). The common point between Casein molecules is structured from two parts: The tail is hydrophobic (meaning that is impermeable), the other end is hydrophilic (or attracted by water). The hydrophobic side will attach to the air bubbles, while the hydrophilic part is associated with milk. This gives the milk foaming properties when moderately heated.
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However, if the milk is too hot, the proteins will be broken down or completely denatured, releasing all the air – which means that the liquid does not foam. This is why it is essential to try to bring as much air into the milk as possible before it reaches room temperature – about 37 ° C (100 ° F). At the same time, the Milk Heating process also enhances the sweetness of the milk. The naturally occurring long-chain carbohydrates (sugars) found in milk will be broken down into simple sugars; the more straightforward the carbohydrate molecules, the easier it will taste. Finally, steam not only adds air and warms the milk, but also creates thrust for the centrifugal movement in the cup. By correctly positioning the steam wand (placing the rod slightly off the center of the milk cup to form a spiral when Steam), the movement of the vortex will eliminate the large air bubbles formed during the whipping process. This is because air is lighter than milk, so large bubbles will float to the surface and form a dense layer. It is challenging to pour artfully into Espresso.  

The effect of milk fat on milk foam

You may have heard someone say skim milk is better for skimming than regular milk. Then another barista thought pure dairy was the best for Steam. If viewed correctly, both of these views will not be the opposite! The fat in milk does not have much effect other than destabilizing the foam. This is because the hydrophobic portion of the milk protein (Casein) can attach to fat instead of attach to air bubbles. So the more fat there is in milk, the less bubbles we have. With this in mind, skim milk will deliver bubbles with the most stable and durable structure possible. However, this foam is difficult to pour the art of a latte, instead of flowing smoothly out of the cup, the skim milk tends to float “floating” on the container.
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In summary, whole milk tends to produce a smooth, stable foam and is more suitable for preparation. After all, the purpose of steam milk is to create an emulsification system between milk, protein, and fat, rather than just “bubbling.”  

Whipping milk for Cappuccino and Latte

While both Cappuccino and Latte are made in a combination of Espresso with milk and foam, But because Cappuccino requires a ratio of Espresso / hot milk/foam = 1/1/1, the milk foam layer will be thick. Equals the amount of liquid in a cup. Mainly Latte is less foam and more liquid in the ratio of 1 Espresso / 2 parts milk with thinner foam layer. Here are three key stages and essential considerations when preparing milk for these two drinks:   Step 1: Prepare the milk
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In the beginning, keep the milk shift upright, while the wand is slightly 1 cm deep (just above the head) and record at an angle of about 30 ° to the surface. It is recommended to use a metal emulsifier, with a measuring line (ml), the better, as metal transfers heat well, making it easy to feel the direct heat of the milk. It is best to use purified, refrigerated milk 1 – 3 ° C before pouring into the shift (250ml for ca 600ml capacity, 200 ml for 450ml variation). For an Espresso machine, you should steam for a second, using a towel to wipe off the Steam to remove any excess milk or water from the tap, until only Steam remains.   Step 2: Whisk (Stretching)
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Start the air hose, when the milk starts to swirl, lower the shift to hear the loud “clink” to create more bubbles. Stop foaming before 37 ° C (100 ° F, slightly warm) – Or when the amount of foam in the shift is almost doubled compared to the original milk level (for cappuccino); Particularly, Latte stops creating foam, when the foam rises 2-4cm from the unique milk level.
  • While milking, pay attention to hear the “creaking” produced by Steam, the “creaking” the more the milk surface vibrates, the more air it takes in to form the foam.
  • When milk is hot above 37 ° C, continued foaming creates a risk of developing large, long-lasting bubbles.
  Step 3: Create a stable spin (spinning) and finish
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When you have enough foam or the milk is hot, you need to tilt the cup a little, let the air nozzle at the edge of the bowl, just flood the milk foam, and maintain a spiral flow. At this point, the milk temperature reaches about 60 – 65 ° C (140 -150 ° F) to clean the steam wand, returning to the old position. Eddy currents will help dispel large bubbles in the Stretching stage to make milk smooth. During this period should not appear “clutter,” just keep the whirlpool and do not put the head slightly submerged in the liquid because the heat will cause protein denaturation, melting all microbubbles. In the end, there will be no holy technique to milk a perfect cup of Cappuccino, perseverance training and continuous learning is the most important skill that you need to equip!

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