What is Crema?
When hot water hits coffee powder under high pressure, it will emulsify the insoluble oil of coffee powder and dissolve a large amount of carbon dioxide supersaturated, which is much larger than the solubility of hot water under normal pressure. this is why countless small foams immediately appear when the liquid flows from the handle. But this does not fully explain the "Crema", open a can of Coke, we can see countless bubbles coming up, but they simply do not last.
To produce stable bubbles, we need some bubbles and some compounds to "wrap" the bubbles, making the bubble structure stable and elastic. The process of this chemical reaction can be thought of as the role of a surfactant. Unlike milk bubbles, which do this through egg whites, coffee uses a substance called protein melanin. It is produced by a chemical reaction of a group of mixtures during baking. In fact, scientists do not know much about the process. Neither protein nor melanin is hydrophilic, so when hot water strikes, they are naturally distributed on the surface of bubbles, so they can come into contact with more air, resulting in countless small bubbles, so we have-bubbles. There are other things-fat (the author refers to both oil and fat, fat is solid, oil is liquid), the presence of oil often destroys the structure of foam (think about it, when we make a cake, we have to remove the yolk, otherwise the fat in the yolk will lead to the failure of egg whites (that is, quickly stirring egg whites and beating them into milk bubbles).
So will the oil in the coffee cause crema to disappear quickly in a few minutes? The answer is both right and wrong. The surfactant is dissolved in water, and due to the action of gravity, the surfactant of the bubble surface will be pulled off the surface of the foam together with the water, making the foam fragile, robbing elasticity, and then quickly disappearing. The speed at which the foam disappears is related to the speed at which the water is dragged away, but the foam on the surface of a cup of coffee lasts much longer than the foam on the surface of a cup of coffee, because the liquid is much thicker than it is quickly flushed. This is also confirmed by our taste.
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Coffee is hard to come by. Please empty the cup.
Every cup of coffee you drink takes three years to blossom and bear fruit, and it goes through complicated procedures such as harvesting, processing, roasting and so on, coupled with the careful preparation of coffee brewers. Therefore, first drink a sip of black coffee without sugar and cream while it is hot, and feel the flavor of the coffee before applying fat powder, which is moderately sour and bitter, rich in layers, and the unique taste with a long finish will bring
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How to use the coffee powder press?
Baristas all know that when using an espresso machine, the hot water brewed has about 9 atmospheric pressure (of course, this is not a fixed value, there are 12 atmospheric pressure or higher), and the pressure is very high, when the water penetrates the coffee cake. the water is inert. What is inertia, that is, water penetrates through the weakest part of the coffee cake, not from the thickest
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