Coffee Brewing Technique Sticker: Extraction, Concentration and Brewing Ratio

The key to making good coffee is to understand the extraction process of each brewing method. The most common defects of coffee, such as bitter, sour, light and astringent, are caused by poor extraction control. Good extraction is the root of delicious coffee. The flavor of the finished coffee is clear, and its variety, origin, processing and baking methods can be obviously shown through the flavor. The physical extraction process of coffee makes all kinds of soluble solids and gases release their own flavor, while the insoluble coffee fiber particles, protein and oil also contribute to the alcohol thickness and texture of coffee. To be honest, the most important goal of brewing coffee is extraction, and the meaning of all extraction variables is to serve it.

The importance of concentration is second only to extraction. The term is confusing, especially when we often see the concentration reference on canned instant coffee, which tries to express how good the dark substance is in coffee. In short, the concentration is the non-aqueous percentage of coffee. There seems to be nothing to say, but the appropriateness of the mixture of coffee and water (that is, the proportion of brewing) is the defining factor for judging the taste of coffee or strong or subtle. But in the final analysis, it depends on individual taste.

Extracted variable

A variety of different cooking ratios can achieve excellent extraction results, but if you want to do this, many factors must be taken into account. There is no doubt that grinding particle size and contact time with water are the two most important factors. The smaller the grinding particle size is, the larger the surface area of coffee is and the higher the extraction rate is, and the extraction effect can also be enhanced by prolonging the contact time between coffee and water. No matter which brewing method, if these two variables are balanced, they can lay a good foundation for a balanced and delicious cup of coffee. Studying grinding, dosage and contact time with water, discovering unknown wonders and creating untasted flavors is also one of the joys of brewing coffee. For example, Philharmonic pressure's brewing method is never fixed, as long as the grinding particle size matches the brewing time, various styles of delicious coffee can be made. When it comes to contact time with water, we have to discuss the topic of percolation coffee, which is made by injecting brewing water into the coffee powder layer and liquid percolation filtration device. this method includes espresso, filter (including hand brewing), and some degree of siphon and mocha pots. In this model, we find that brewing ratio, grinding size and brewing time are all relative to each other, because coffee itself is an obstacle to the flow of water.

Cooking temperature is also very important. The higher the temperature, the faster the reaction takes place, which is universal in most cases. In the case of coffee, the higher the temperature, the faster the extraction. Different compounds have different extraction thresholds, such as caffeine at very low temperatures below 30 ℃), but some astringent compounds can only be extracted when they are close to 100 ℃, which is why we should avoid brewing coffee with water above 95 ℃.

These are not the only factors that affect the extraction. The stirring strength of cooking water is directly related to the water pressure, so it can also affect the extraction rate. When making espresso, it is because of high pressure that water can repeatedly flow in and out of the porous structure of coffee powder. If you have ever been in a hurry to make tea, you will notice that stirring the tea bag quickly can change the color of the tea more quickly than letting it sway in boiling water. Quick and slow stirring during cooking, or specific water injection and moistening methods can improve the efficiency of the cooking process, thus producing finished products with different effects. Some baristas even regard their hand flushing skills (in the form of manual flushing during the water injection stage) as a gift from heaven. There are countless ways to inject water, which once again proves that coffee brewing is a mysterious thing that is difficult to talk to people.

The freshness of coffee can also change the extraction process. Especially fresh coffee beans release large amounts of carbon dioxide, a gas that acts like an invisible barrier that prevents coffee from coming into contact with water. For this reason, the coffee beans used to brew espresso must be placed at least 5 days in advance, otherwise the air pressure on the surface of the coffee beans will compete with the gas and water in the filter, and the coffee will eventually suffer. Of course, any coffee beans should be left at rest for 8 hours before grinding and brewing, so as not to interfere with the cooking process by carbon dioxide.

Cooking control chart

This figure depicts the best combination relationship between coffee concentration and coffee extraction rate (not suitable for espresso brewing). The vertical axis represents the concentration of coffee, or TDS (total dissolved solid), expressed as a percentage of the actual coffee product. The horizontal axis represents the extraction rate (yield), expressed as a percentage of the amount of coffee powder dissolved in water to the original dry coffee powder dose. The lower the chart, the lower the coffee concentration, and vice versa, the higher the concentration. Different people's preference for coffee may be distributed in various areas of the picture, after all, the preference for coffee concentration varies from person to person. The brewing ratio directly affects the concentration of coffee. Coffee that falls in the central gray area is generally considered perfect: its concentration and extraction rate are well balanced (the extraction rate is between 18% and 22%, and the concentration is between 1.1% and 1.3%), and the product is sweeter, more mellow and more transparent. The diagonal gray line represents the extraction rate, which succinctly shows what kind of cooking product is too light or insufficient extraction, and what is too thick or too bitter.

The following picture looks at the coffee fat on each serving of espresso. Its color and persistence are part of the basis for judging whether the coffee is successfully extracted.

Measurement of extraction rate

The best analogy concept of extraction rate is the percentage of output, that is, the percentage of coffee dissolved into the brewed product (by weight) to its original dry powder state. This value represents the efficiency of the extraction process and helps us to understand whether the final product is in equilibrium. The principle of extraction rate applies to all brewing methods, and interestingly, even if the concentration of espresso is much higher than that of filtered coffee, the percentage of output is roughly the same. The reason is simple: espresso has much less water content.

For half a century, many studies have been carried out to find out the extraction rate of coffee used for brewing in order to produce a satisfactory finished product. Coffee with a dry weight of about 1 stroke 3 is soluble in water, that is, it can be extracted. However, not all soluble substances are what we want. Coffee professionals generally believe that the acceptable range of extraction rate is 18% ~ 22%, which is equivalent to only half of the soluble substances have won the opportunity. Coffee below or above this range is called underextraction or overextraction. The coffee with insufficient extraction (the extraction rate is less than 18%) is usually sour, thin, light, monotonous and uncharacteristic, while the coffee with excessive extraction (the extraction rate is higher than 22%) is more bitter, gray and astringent. One thing to say here is that this tolerance limit of only 4% was compared by coffee research groups based on sensory analysis of hundreds of brewed coffee samples, not a fictional product. Of course, the rules are variable, especially for boutique coffee, whose baking style determines the best yield of the finished product. For example, when the extraction rate of some coffee is 16%, its flavor is bright, clean and fruity; when brewed to about 20%, it shows the flavor of jam and candy. At that time, it was proposed that the flavor of coffee reached the best at the extraction rate nodes of 16% and 20%, while the extraction rate range of 17% ~ 18% was not available at all. I don't quite understand why the taste goes down between the two peaks, but use the Manhattan cocktail as an analogy: dry and sweet are delicious, but the taste in between is mediocre. Sometimes, we just like one or the other.

You can calculate the percentage of coffee output at home: first weigh the coffee before brewing (to meet standard operating procedures), then dry the remaining coffee in a low-temperature box and weigh it. The percentage value in decimal form can be obtained by calculating the difference between the two samples and dividing it by the original coffee weight. Of course, this method takes several hours, and the operation process is not very accurate. If you have plenty of wallets, you can buy a coffee refractometer (such as one made by VST Lab). The refractometer uses refracted light to measure the liquid concentration of brewed coffee, and only 2 milliliters of cold coffee samples can display the readings digitally. You can also use the conversion table to calculate the TDS value of coffee to determine the yield of soluble substances.

Cooking ratio

Another important factor that needs to be paid close attention to in the cooking process is the cooking ratio. This value is the weight ratio of the coffee liquid to the coffee, which is used to indicate the concentration of the coffee product. The brewing ratio of espresso is usually about 1.5 ∶ 1, that is, one serving of coffee corresponds to one and a half parts of coffee liquid, that is, 20 grams of coffee can produce 30 grams of espresso. The standard ratio of French filter pot brewing is about 15 ∶ 1, that is, 20g of coffee can produce 300g of drink. Because coffee hinders the absorption of some water-2 grams per gram of coffee, it is important to remember that it is calculated based on the total weight of the coffee product rather than the weight of the water used for brewing.

You may wonder, what does the taste of coffee have to do with these numbers? How can you be bound by a few charts and formulas? Indeed, human taste and olfactory systems are ancient and excellent, and they are not only more sensitive than any digital refractometer, but also the ultimate determinant of whether a cup of coffee is good or bad. You should let your mouth tell yourself what tastes good, and then write down every step to achieve this effect. These science-oriented numbers seem like the art of measurement, but only when you respect the artistic feelings and scientific principles in them, it is a realistic proposition to control these variables as much as you can.