Coffee common sense espresso is the essence of coffee

In terms of pure sensory entertainment, there are few experiences in daily life that can be comparable to a good cup of coffee. The charming fragrance of a cup of hot, smoking coffee just brewed from freshly roasted beans can pull sleeping people out of bed and lead passers-by into the cafe. Millions of people around the world would have trouble getting through the day without a bout of sanity caused by the caffeine in their coffee. Only in this seemingly ordinary drink, but there is a very complex chemistry. Various ways from the production and roasting of coffee beans to the preparation of coffee have a subtle impact on hundreds of chemicals and define the taste, aroma and texture of coffee. If there is no in-depth understanding of the above, it will be a rare opportunity and pure luck to have a good cup of coffee.

Connoisseurs agree that espresso (espresso) is the essence of coffee: a small, strong magnetic cup filled with a half-full dark, opaque drip filtrate with a mellow, reddish-brown foam called crema. Klima is composed of fine bubbles wrapped in thin film, which is closely related to the unique taste and flavor of coffee, as well as its heat. The word Espresso is meant to be made upon request. As for the practice is to grind the roasted coffee into fine grains, press it into a cake, and filter it quickly with a small amount of pressurized and heated water. The resulting concentrated liquid contains not only melted solids, but also a large number of various spice substances in the scattered tiny oil droplets suspension. All these add up to the unique strong taste, smell and "taste" of espresso.

Addicts believe that the perfect espresso is the best because of its special preparation method, which shows and strengthens the natural characteristics of coffee beans. In fact, espresso is the essence of all kinds of coffee-making methods, from the Turkish method to various leaching methods to filtering leaks (see the introduction of other coffee-making methods in the text box on the page); as long as you know the practice of espresso, you know all the forms of coffee making, so it is more appropriate to take it as an example.

High-quality coffee comes from maintaining tight control over a variety of factors, from soil to plants to cups. There are countless variables in the cultivation of coffee that must be paid attention to and control. once the coffee beans bear fruit, the quality has been determined, and nothing can be added or removed. For an espresso, it takes 50 to 55 beans; one imperfect bean is enough to cause pollution. That's because the human sense of smell and taste begins with a self-defense mechanism to protect our ancestors from decay, that is, unhealthy food. Only by relying on modern technology can it be economical and stable to identify 50 perfect coffee beans.

Grow coffee

Raw coffee beans are the seeds of Rubiaceae, and there are at least 66 species in the genus Coffea. Two of the commercial interests are Arabica (Coffea arabica) and Congolese coffee (C. canephora). The former accounts for 2/3 of the world's production, while the latter, also known as Robusta, accounts for the remaining 1/3. Robastian coffee and all wild coffee have 22 chromosomes, while Arabica coffee has 44. As a result, Arabica coffee cannot be bred with other kinds of coffee to produce hybrid plants.

Robasta coffee is a high-yielding and pest-resistant plant that can reach a height of up to 12 meters and grows best in warm and humid climates. Coffee made from robastian beans is quite substantial, relatively strong, has a local flavor, and is high in caffeine, accounting for 2.4% to 2.8% of the weight. Although many suppliers sell robastian coffee, this kind of coffee beans fail to produce the highest quality coffee.

Arabica coffee, which originated in the highlands of Ethiopia, is a delicate plant with medium to low yields, with a height of about 5 to 6 meters, but coffee trees cultivated for commercial purposes are all pruned at 1.5 to 2 meters high. They need a temperate climate and considerable care during their growth. Coffee made from Arabica beans has a strong, complex smell reminiscent of flowers, fruit, honey, chocolate, caramel or toast; its caffeine content never exceeds 1.5% of the weight. Because of the excellent quality and taste of Arabica coffee, the price is higher than its strong, coarse cousin.

A good rain will cause Arabica coffee trees to blossom. After 210 days, red or yellow berries appeared. There are two rectangular seeds in each berry, namely coffee beans. Because there are both flowers and fruits on the same branch, the index finger and thumb of the collector are the best tools for collecting ripe berries. Grabbing the fruit from the whole branch with the palm of your hand, or using an automatic harvesting machine, you can't tell the ripe berries from the green berries.

The factors that determine the final quality of coffee beans depend on the plant's genes, the soil in which they grow and the climate of the local area, including horizontal height, Rain Water and sunlight, as well as daily temperature changes. These agricultural and geological considerations cause differences in the taste of many different coffee beans in the process of roasting; suppliers mix them to create a variety of special mixed products on the market.

Processing coffee

Coffee beans must be disposed of immediately after harvest so as not to go bad. The producer will use two methods of treatment: the sun method and the cleaning method. An effective way to bask in the sun is to spread the berries flat in the yard and stir the dehydrated berries from time to time to make them evenly heated and breathable. Then put the dried berries into the machine, crush the shell, and remove the shell and a parchment film at the same time, separate the coffee beans, and then sort and bag them. In another way, the berries are mechanically removed, washed, dried and separated from the sheepskin-like outer membrane. Either way, the first goal is to reduce 65% moisture in coffee berries to only 10-12% raw (green) coffee beans.

One of the biggest challenges to making good coffee is to make sure to start with good raw coffee beans. Top manufacturers, such as Yili Coffee in Trieste, Italy, use many complex labor management techniques to reduce the proportion of defective coffee beans. These include the use of ultraviolet fluorescence analysis to pick out moldy beans and the use of tricolor images (yellow-green, red and infrared) to establish color fingerprints for each batch of beans. The Italian Coffee Company has partnered with the British company Sotex to develop a two-color light classification system to do the final quality control before raw coffee beans are roasted. The way is that the photodetector picks out the bad beans from the beans that fall on the plate, and then removes them separately with a blow from the air nozzle. This classification operates at a speed of up to 400 beans per second, which is not comparable to that of any man, and its accuracy is not as accurate as that of the most trained human eyes.

A perfectly mature raw coffee bean, made up of unusually thick-walled cells, can be as thick as 5-7 microns, which is rare in the plant world. During baking, these cells with a diameter of 30 to 40 microns act like microreactors, where all the important chemical reactions driven by heating take place, resulting in the fascinating taste and aroma of coffee. On the one hand, the cell wall of immature coffee beans is thin, and there is no important flavor protein precursor produced in the final stage of ripening. These important substances in the cells are also emptied from beans fermented by bacteria or mold.

Roasted coffee

Roasting is a process driven by heat, which greatly increases the complexity of coffee. The aroma of raw coffee beans contains about 250 different volatile molecules, but more than 800 are found in roasted coffee beans.

In the process of staged heating in a roaster (usually using a large hot rotating cylinder), the remaining water in the coffee bean cells is converted into steam, prompting the rich carbohydrates, proteins, lipids and minerals to undergo a variety of complex chemical reactions (see the text box on the second page). According to the famous Maillard reaction (Maillard's reaction), carbohydrates combine with amino acids, meniscus, and proteins to caramelize at temperatures of 185 to 240 degrees Celsius. The end product is yellowish brown, bittersweet glycosylamine (glycosylamine) and melanin (melanoidin) (the main source of coffee flavor), as well as carbon dioxide (up to 12 liters of carbon dioxide for every kilogram of coffee beans baked).

At the same time, there are a variety of lower-quality aroma molecules; these volatile compounds give coffee a familiar aroma. When water vapor and carbon dioxide try to escape from thick, porous cell walls and a layer of grease, the pressure in each cell can rise to as high as 20 to 25 atmospheres. Some cells do crack, producing the typical popping sound of roasting coffee beans. During the baking process, the size of the coffee beans increased by half or more; the quality of the beans decreased by 1/5.

Depending on the temperature and process applied, the baking time can range from as little as 90 seconds to as long as 40 minutes, but the traditional time is 12 minutes. Depending on the baking time, the thermodynamics of the intracellular reaction and the final results are also different. The use of a large amount of heat can shorten the baking time and reduce weight loss, but the coffee produced by this method has a bitter taste of metal, which is due to the lack of sufficient reaction time and the residue of polyphenols. Areas with poor economic conditions usually use baking for a long time, because most consumers can only afford low-priced, defective coffee beans, so they have to bake for a long time to drive out the bad taste and aroma. Unfortunately, the popular taste and aroma are gone, leaving only a rather bitter taste.

The higher the temperature used in baking, the worse the aroma and bitterness of the coffee. At the same time, the acidity emerges.

Smell coffee

The science of aroma is a highly complex science. Researchers usually use a gas chromatograph and an olfactometer to analyze the aroma produced when coffee is roasted. The so-called olfactory meter allows experienced testers to smell each flavor that can be separated and identified, and then define it. Next, mass spectrometers are often used to further distinguish the chemical composition of each odor. The smell of roasted coffee separated from the gas chromatography and inhaled into the nose is an enlightening experience. Some people can smell roses, Darjeeling Tea, chocolate, vanilla and violets, as well as truffles, soup, cheese, sweat and even the so-called cat smell. The latter smells like white wine (sauvignon blanc wine) when diluted, but at high concentrations, it tastes disgusting.

In the Yili Coffee laboratory, technicians focus on the strongest flavors. Readers can imagine you are listening to a recording of an 800-member choir, including several good soloists like Jessie Norman and Pavarotti. When you turn down the volume, even if the sound of the choir fades away, the prominent solo can still be heard. Diluting the aroma of coffee is a similar situation: after a certain dilution point, only the strongest substance can be felt. Unfortunately, the strongest molecules in the coffee sample come from defective coffee beans.

Molecules such as ethyl butyrate (ethylbutanoate) and ethyl glycolate (ethylglycolate) are responsible for the unpleasant smell of immature coffee beans; as long as they exist, a cup of coffee is ruined. Similarly, the molecules that contribute to the earthy, chemical signature flavor of Robasta coffee are methylisoborneol and trichloroanisole (TCA). TCA is also known as the "flavor of Rio" because it was first found in coffee grown near Rio de Janeiro and can also be found in cork-sealed wine. The threshold of the human olfactory system for this substance is so low that it can be smelled at a concentration of 6'10-15 g/ml.

Make coffee

The next important step in turning roasted coffee beans into a cup of espresso is to use hot water to extract the active substances from roasted and ground coffee beans. However, for brewing a cup of ordinary filter coffee and a cup of espresso, the interaction between hot water and coffee powder is subtly different.

When coffee is prepared by filtering and dripping, hot water passes through a loosely stacked coffee powder of medium size. Within 4-6 minutes of contact with hot water, most of the soluble substances in the coffee go into the aqueous solution. As a result, coffee contains a lot of soluble acid and caffeine. Conversely, it takes much less time to make espresso, with less acid and 60-70% caffeine entering the filtrate.

Making espresso requires special equipment that heats the water to 9294 degrees Celsius and pressurizes it to nine atmospheres. The way to do this is to first put the coffee powder ground into fine to medium particles in a filtering container and squeeze it down hard to form a solid structure. Because there is a layer of oil that is as viscous as honey on the periphery of the particles, the pressed coffee powder attaches to each other, forming a dense maze of small air channels. Experiments show that the resistance of this coffee powder to water must be slightly less than the pressure of hot steam so that the water can pass through it at a speed of about one milliliter per second.

Using the generally recommended 30-second steaming time, experienced coffee bar chefs produce about 30 milliliters of espresso liquid, which is covered with a layer of extremely important Klima. If the color of the foam is too light, it means that the espresso extract is not enough, it may be because the coffee is not carefully ground, the water temperature is too low, or the time is too short. If Klima's color is very dark and there is a "hole" in the middle, it is likely that the coffee powder is too fine or the amount is too large. Overextracted espresso is either a white foam formed by large bubbles, or a white spot in the middle of the cup; the former is due to the high temperature of the water, while the latter is steamed for too long.

In the process of the filter droplets, the ingredients on the surface of the coffee powder are also washed off, including scented oil droplets and part of the cellular structure. The high pressure produced by the espresso machine emulsifies a small amount of oil, containing about 0.1 grams per cup of coffee. Intact cells in coffee powder produce fine foams caused by gases (especially carbon dioxide) passing through pores in the cell wall. Some particularly fine coffee powder, together with fragments of the cell wall, will also enter the coffee drink, causing the foamy Klima to have the appearance of the so-called tiger skin. The final product is a polyhedral colloid with water molecules combined with dispersed bubbles, oil droplets and solid fragments, all of which are no more than 5 microns in size. These dispersed colloid properties result in the high texture, high adhesion and low surface tension of espresso. As a result, espresso clearly fills the surface of our tongue and continues to release volatile aroma molecules dissolved in emulsified oil droplets as long as it exists for a moment. The oily carriers with these smells and aromas mean that the excellent taste and aroma of a good espresso is still memorable after 20 minutes of drinking. Fortunately, drinkers don't need to know anything about the complex chemistry of coffee to enjoy it.