The production of Espresso

Production of Espresso: matching

Generally speaking, large coffee beans can produce better coffee. In the case that the quality of coffee beans has been fully assured, the first technical problem to be solved is "blending". "blending" refers to the selection of coffee beans of different origin and quality to achieve the desired results. The "matching Technology School" believes that 50% of the success factors of a perfect Espresso depend on the composition and quality of the match. No single-origin coffee can fully achieve the taste required by Espresso. Coffee beans from African and Arab coffee trees are characterized by complexity, large amount of berries and floating aroma, while coffee from Latin America is clean, strong and refreshing, while coffee from Southeast Asia is characterized by full fruit and earthy flavor. Many coffees are a mixture of several types of coffee, making the taste more complex.

The Espresso boiled at the ideal water temperature is dark reddish brown, with dark brown spots on the surface of the foam (called "el tigre" by the Italians), and the foam should be more than 4mm thick.

A perfect match is not a random mix of several boutique coffee beans. The basic blending process is to first determine the benchmark beans, then add coffee beans that can increase flavor and special flavor, and form a blend of coffee according to the mixing proportion and roasting degree of all kinds of beans. Raw beans for blending should have their own characteristics to avoid similar flavor. The quantity and proportion of coffee beans depends on continuous attempts, so most of them draw up a matching schedule by mathematical combination before blending, and then determine the best plan through the process of assembling cups.

Bake before matching, or match before baking? This has always been a topic of debate between bakers and assemblers. As with wine, blending before baking can make the aroma and quality more uniform, but the "decay" of roasting must be taken into account, as coffee from different places requires different baking time and temperature. If you have a definite recipe, you can put different coffee beans together and then bake them together. Most long-established coffee makers have their own secret recipes.

In contrast to the "blending technology school", the "baking technology school" believes that the taste of coffee depends 80% on roasting. Regardless of the percentage data, whether you are particular about the degree of "roasting" and whether you bake it yourself, this has indeed become an important indicator to verify the identity of a coffee glutton. "roasting" refers to roasting the raw coffee beans with a special machine to make the coffee beans show a unique brown color, aroma and taste. The key point is to "stir-fry" the inside and outside of the beans evenly without being overburnt. A series of chemical changes occur during baking: moisture decreases from 10% to 1%, fat from 12% to 16%, sugar from 10% to 2%, chlorogenic acid from 7% to 4% to 5%, and nitride from 12% to 14%. The physical change is: water loss, weight reduction of 10% to 15%, volume increase of 60%.

A vivid analogy is: "the roaster is a machine between a popcorn machine and a clothes dryer." The temperature in a large industrial baking bucket can reach 288 degrees Celsius, and the coffee beans first turn yellow and smell like popcorn. After about 8 minutes, it began to snap and expand, and when the temperature reached 204 degrees Celsius, the coffee beans began to turn brown and the oil began to spill out. The spilled oil is called "caffeine" or "caffeine", and the chemical reaction between calories and caffeine is called "pyrolysis", which produces a strong coffee flavor. In another 3 to 5 minutes, there will be another snapping sound in the machine, and the color of the coffee will soon change to a dark color, indicating that it has been baked. When the preset baking temperature is reached, cold air can be used to stop baking. The well-roasted coffee beans have no wrinkles on the surface and the gloss is symmetrical, which fully demonstrates its unique flavor. If you are too impatient at the beginning of baking, there will be spots on the bean skin and the taste will become bitter and choking.

In 1992, the second generation of Yili managers commissioned architect Matteo Thun to design a set of white coffee porcelain cups, which gave birth to a series of popular Italian coffee collection cups. Every year Yili invites modern artists to work together to design the annual collection cup. Despite the ever-changing exterior decoration, the cup itself has always strictly followed the Italian family's definition of the perfect Espresso coffee cup: "A small thick-walled porcelain cup with a capacity of no more than 50ml." Small capacity to ensure that the drinks are more concentrated; use synthetic materials to ensure that the foam and liquid parts are as clear as the liquid. "

Generally, roasting is divided into shallow, medium and deep degrees, and the baking time varies depending on the type of coffee required. The light roasted coffee beans are light and sour, the intermediate roasting is sour and bitter, and the deep roasting color is rich and bitter. The lighter the roasting degree is, the stronger the sour taste of the coffee bean is, the deeper the baking degree is, the sour taste is gradually lost, and the bitterness is heavier. Professional baking methods are usually divided into the following eight stages: very shallow baking (Light Roast), shallow baking (Cinnamon Roast), micro baking (Medium Roast), medium baking (High Roast), medium and deep baking (Cicty Roast), deep baking (Full-City Roast), very deep baking (French Roast) and very deep baking (Italian Roast). Deep baking, also known as "Italian baking", is mainly popular in Latin countries and is considered to be the most suitable for Espresso. The color of the very deep-roasted coffee beans is black, and the oil has infiltrated to the surface, so it has a bitter taste of carbon ash, and the mellowness is significantly reduced.

For some strict baking techniques, roasted coffee used in Espresso should also be fresh, so coffee roasted within four days is required. But I'm afraid this rule only applies to gluttons who bake on their own small machines. Big coffee factories have a variety of patented technologies to ensure the sealed preservation of roasted coffee beans, the more famous of which is Illy's inert gas preservation method, which has been patented since its inception, which removes the air from the container and pours it into the pressurized inert gas. The observation under the electron microscope can confirm that coffee oil is scattered sporadically in the coffee cell tissue, and after pressure, these oils will be concentrated around the cell wall, wrapping some fragrant and highly volatile chemicals in the cells, thus isolating air contact and avoiding oxidation. The technology is believed to maintain the flavor and freshness of roasted coffee beans for up to three years.

Production of Espresso: grinding

The thickness of coffee beans depends on the way they are cooked. Generally speaking, the longer the cooking time, the thicker the ground powder. In terms of actual cooking, American filter coffee takes a long time to make, so coffee powder particles are the thickest, "siphon" coffee powder takes more than a minute to cook, and coffee powder particles are medium in size; Espresso takes the shortest time, so the particles need to be ground the finest. "Grinding Technology School" believes that grinding the right size of coffee powder is essential for the perfect coffee. There is a theoretically ideal time for the extraction of water-soluble substances in coffee powder: if the powder is very fine and boiled for too long, it will cause over-extraction, and the coffee may be very bitter and lose its aroma; on the contrary, if the powder is too coarse to make it boil too fast, resulting in insufficient extraction, the coffee will be tasteless. Particle size can be discussed, and the shape of the grinding blade is also available in flat or tapered shape. one of the technical points about grinding is recognized: it must be ground before cooking. After the coffee bean is ground into powder, due to the increase of surface area, it is easy to absorb moisture and be oxidized, resulting in flavor damage. The limit of placement time provided by some "grinding technology pie" is: 30 minutes.

After grinding the coffee powder, it seems that it is finally possible to make a cup of technical Espresso according to the technical standard proposed by AndreIlly in his book Espresso Coffee: a quality of Chemistry (Espresso Coffee:The Chemistry of Quality). Indeed, Andre Yili belongs to the famous Illy coffee family. The family invented the first automatic Espresso coffee machine to replace steam with compressed air in 1933, which became the prototype of modern automatic Espresso coffee machine, and its technological innovation also accounted for three of the eight historic breakthroughs in the coffee industry. So, no matter which technical school you measure, the standard from the Illy family has become a classic description of some kind of Espresso: "using 7 grams of freshly ground coffee powder, using water at a temperature of about 91 degrees Celsius at 9 atmospheric pressure (Bar), through 25 seconds of extraction to get a cup of about 30 milliliters of coffee drink, the surface of this coffee should be covered with a reddish-brown foam (Crema)."

Andre-Yili also modestly admitted that this standard is only based on his own experience, how to extract a perfect cup of Espresso, the technical discussion has only just begun. For example, senior American barista David Schummel (DavidSchomer) believes that the best Espresso requires 8.2 atmospheric pressure and 95 ℃ cooking temperature. The question that comes with grinding should be, how much coffee powder is put in the filter handle (filterbasket)? How to make powder and press powder? But another technical question often cuts in: where should the filter handle be put in your spare time?

The view represented by Taiwan in Asia is that as most of the aromatic components in coffee powder are volatile, if the handle of the filter is preheated in advance, a large amount of aromatic substances will be lost during filling, which is very harmful to Espresso. The common view in Europe and America is that the filter must be fastened to the group when it is not in use, so that it can preheat and reduce the impact of temperature difference. In his book "Espresso Coffee Specialty" (Espresso Coffee:Professional Techniques), Schummel pointed out: "the effluent of the coffee maker boiler can be maintained at ±1 ℃, but it is another matter to keep the temperature of the head steady. The machines I have tried have a change of at least 6 ℃. The structure of the filter handle itself is a little responsible. It itself is made of heavy metal for the purpose of heat preservation. But the metal is easy to dissipate heat. Take the handle off the machine, put coffee powder in it, and press it. Throughout the process, the metal parts continue to dissipate a lot of heat, and eventually the temperature will be 20 ℃ lower than originally expected. " To achieve optimal temperature control, most commercial Espresso coffee machines for cafes use brass head and stainless steel strainer, but this "luxury" is hard to see on household machines.

Production of Espresso: loading powder

Where to put the filter handle is a matter of opinion for the time being, let's see how to load the powder. Andre Yili has a short sentence of "7g", but in the eyes of some careful people, this stage can be described as "the most difficult step in the cooking Espresso process". The coffee powder compacted in the filter handle is often referred to as the "cake". For Espresso, how much water passes through the coffee cake per second is crucial, because Espresso's "golden law of flow rate" is: "whether it is a single or double dose, the extraction time is about 25 seconds." This can not only fully extract the fragrance of coffee, but also extract the least amount of caffeine and bad-smelling substances. The ground coffee powder has strong hygroscopicity. When the relative humidity of the surrounding environment is relatively high, it will absorb moisture; when the relative humidity of the surrounding environment is relatively low, it will release moisture. Therefore, the thickness of the mill and the amount of powder should be constantly adjusted to ensure a cooking time of 25 seconds.

The strength of cloth powder and pressing powder should also take into account environmental factors. The usual technical requirement is: after the powder is produced, the coffee powder in the handle is pushed evenly with a tamper. Press the powder smoothly once with a force of 5 pounds, then once with a force of 30 pounds, and then with a force of 20 pounds. At the same time, the powder press rotates 720 degrees. If the surrounding humidity is very heavy, the packing pressure will be tighter than before, in order to reduce the extraction rate. Making Espresso outdoors is a test for tough barists. due to frequent changes in outdoor temperature and humidity, truly dedicated baristas are said to adjust their powder pressing techniques in each cup of cooking to suit the climatic conditions on the spot.

It is also important to flatten the filter cake. If the resistance of the filter cake is uneven, it will be washed out of the hole or pore diameter by high-pressure boiling water, resulting in uneven extraction. If the extraction is insufficient, a yellowish-brown liquid will be formed in the cooking head, while the over-extracted part will dissolve other substances and cause white stripes. As for the strength of these "5 pounds" and "30 pounds", how can it be really plain? the real technocrats will only tell you to experience it. Don't trust the filling devices or pressure bars with standard counterweights in the grinder.

It is a matter of wisdom as to whether it is necessary to soften or compensate for a mineral, and technocrats generally prefer the "prepreg" function, which allows coffee powder to fill up with saturated water before starting the main extraction step. A coffee machine with a "pre-soak" function takes 5 to 8 seconds before coffee comes out after turning on the brewing switch. It is said that the reason why "prepreg" is considered important is that, first of all, it can reduce the adhesion of soluble aromatic oils in coffee, making it easier to extract more oil; secondly, it helps to close the top of the coffee filter cake and prevent high-pressure boiling water from rushing out of the cavities, causing uneven extraction.

Water temperature is of course important for the perfect Espresso. Under the ideal water temperature, the Espresso is very deep reddish brown, and the foam on the surface will have dark brown spots (the Italians call it "eltigre"), and the thickness of the foam should be more than 4mm; the water temperature is too low, the coffee is yellowish brown, although the foam is thick, but the color is relatively light, there are no dark spots. Too high water temperature will burn out the coffee grease, the aftertaste is restless, and there will be thick dark black stripes on the foam surface. For technocrats like Schumel, who are extremely sensitive to changes in water temperature, the brewing mouth of the coffee machine can never be trusted, burying the sensor probe directly in the filled coffee cake to monitor the water temperature.

The production of Espresso: cups

After that, you should wait for the dark brown-red coffee liquid to appear steadily in the brewing mouth, but there is also a more perfect technical school that will make more demands on the cup. Needless to say, Andre Italian opened a chapter in "Espresso Coffee: a quality related to Chemistry" to define Espresso cups: "small thick-walled porcelain cups with a capacity not more than 50 milliliters." The capacity is small to ensure that the drinks are more concentrated, and synthetic materials are used to ensure that the foam and liquid parts are as clear as they are. " Andre then explained the chemical meaning of these definitions in more detail. In the eyes of ordinary coffee consumers, the artistic value of Illy coffee cups now exceeds chemical value because of the introduction of limited design editions from time to time, but this does not prevent Illy coffee cups from becoming a model of some kind of Espresso coffee cup design: challenging size is risking becoming an American coffee cup, and challenging the thickness and material of the cup wall will infringe on the cup temperature issues that many technologists care about. Preheating the Espresso coffee cup is a hobby of many technical schools, the ideal temperature is 35-40 ℃, while the more stringent preheating practice is: "the coffee cup should be preheated through a heat source other than the coffee machine." Taking a cup of water from the coffee machine to warm the cup will lower the temperature of the boiler water, resulting in uneven extraction. "

Beyond all these parameters, you end up with a perfect "tiger stripe" Espresso, which some call the "God Shot". Perfect Espresso is the foundation of perfect Capuccino, but more pure Espresso technocrats are not keen on the pursuit of foam flowers and so on. When asked about the end of a perfect Espresso, they would suggest: drink it while it's hot, wash the coffee maker, and get ready for the next one.