Coffee Technique Post: Extraction, Concentration and Brewing Ratio | Coffee lovers are reading

Coffee Techniques: 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 being too bitter, too sour, too light, and too astringent are all caused by poor extraction control. Good extraction is the root of delicious coffee. The finished coffee has a clear flavor, and its variety, origin, processing and roasting methods can be clearly shown through the flavor. The physical extraction process of coffee allows various soluble solids and gases to release their own flavors, while insoluble coffee fiber particles, proteins and oils also contribute to the mellowness and texture of coffee. To be honest, the most important goal of brewing coffee is extraction, and the significance of all extraction variables is to serve it.

Second only to extraction, strength is the most important term. It's a confusing term, especially when we see strength references on cans of instant coffee that try to convey how good the dark stuff is. Simply put, strength is the percentage of coffee that's not water. It may not seem like much, but the right mix of coffee and water (the brew ratio) is the difference between a strong or subtle coffee. Ultimately, it comes down to personal taste.

Extraction variables

There are many different brewing ratios that can achieve excellent extraction results, but there are many factors to consider in order to achieve this. Grind size and contact time with water are undoubtedly the two most important factors. The smaller the grind size, the greater the surface area of ​​the coffee, which increases the extraction rate; longer contact time with water also enhances the extraction effect . When these two variables are balanced, they lay a good foundation for a balanced and delicious cup of coffee, no matter which brewing method is used. It is also a great pleasure to play with grind, dosage and contact time to discover unknown wonders and create flavors that have never been tasted before. For example, the brewing method of AeroPress is never fixed. As long as the grind size matches the brewing time, you can make delicious coffee in various styles. Speaking of contact time with water, we have to discuss the topic of percolation coffee, which is made by injecting brewing water into the coffee grounds and letting the liquid percolate through the filter device. Brewing methods that use this method include espresso, filter (including hand pour-over), and to some extent siphon and moka pot. In this mode, we find that brew ratio, grind size, and brew time are all relative concepts to each other , because the coffee itself is equivalent to an obstacle that blocks the water flow .

Brewing temperature is also very important. The higher the temperature, the faster the reaction occurs. This is true for most things. For example, in coffee, the higher the temperature, the faster the extraction . Different compounds have different extraction thresholds. For example, caffeine can be extracted at very low temperatures (below 30°C), but some astringent compounds can only be extracted at close to 100°C, which is why we should avoid brewing coffee with water above 95°C.

But there are more factors that affect extraction. How hard you stir the brewing water is directly related to the water pressure , and therefore also affects extraction. It’s the high pressure that allows the water to repeatedly move in and out of the porous structure of the coffee powder when making espresso. If you’ve ever made a cup of tea in a hurry, you’ll have noticed that stirring a tea bag quickly changes the color of the tea faster than just letting it slosh in boiling water. Fast or slow stirring, or specific pouring and moistening techniques can improve the efficiency of the brewing process, resulting in a variety of finished products. Some baristas even consider their hand pouring technique (a form of manual pouring during the pouring phase) to be a gift from God. The countless ways to pour water are another proof that coffee brewing is a mysterious thing that is difficult to explain to people.

The freshness of the coffee can also change the extraction process. Especially fresh coffee beans will release a lot of carbon dioxide, which is like an invisible barrier that prevents coffee and water from coming into contact normally. For this reason, coffee beans used to brew espresso must be left to stand for at least 5 days in advance, otherwise the air pressure on the surface of the coffee beans will compete with the air and water in the filter itself, and the coffee will be the one that suffers in the end. Of course, any coffee beans should be left to stand for 8 hours before grinding and brewing to prevent carbon dioxide from interfering with the brewing process.

Brewing Control Chart

This graph depicts the best combination of coffee strength and coffee extraction (not applicable to espresso brewing methods). The vertical axis represents the strength of the coffee or TDS (total dissolved solids), expressed as a percentage of the actual finished coffee. The horizontal axis represents the extraction rate (yield), expressed as the amount of coffee powder dissolved by water as a percentage of the original dry coffee powder dose. The lower the graph, the lower the coffee strength, and vice versa. Different people's preferred coffees may be distributed in various areas of this graph. After all, the preference for coffee strength varies from person to person. The brewing ratio directly affects the strength of the coffee. Coffees that fall in the central gray area are generally considered perfect: they have a proper balance of strength and extraction (extraction between 18% and 22%, and strength 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 concisely shows what kind of brewed product is too light or under-extracted, and what kind is too strong or too bitter.

In the picture below, observe the coffee crema on top of each espresso. Its color and persistence are part of the basis for judging whether the coffee is successfully extracted.

Extraction rate measurement

The best analogy for extraction is the yield percentage, which is the percentage of coffee (by weight) that is dissolved into the finished brew compared to its original dry state. This number represents the efficiency of the extraction process and helps us understand whether the final product is balanced. The principle of extraction applies to all brewing methods, and interestingly, even though espresso is much more concentrated than filtered coffee, the yield percentage is roughly the same. The simple reason is that espresso also contains much less water.

For half a century, many parties have conducted research to try to figure out what extraction rate of coffee used for brewing can produce a satisfactory finished product. About 1/3 of the dry weight of coffee 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% to 22%, which is equivalent to only half of the soluble substances getting a chance. Coffee below or above this range is called under-extraction or over-extraction. Under-extracted coffee (extraction rate below 18%) is usually sour, thin, light, monotonous and featureless; over-extracted coffee (extraction rate above 22%) is increasingly bitter, gray and astringent. It should be noted here that this tolerance limit of only 4% was compared by various coffee research groups based on the sensory analysis of hundreds of brewed coffee samples, and is not a product of fiction. Of course, the rules are variable, especially for specialty coffees, whose roasting style determines the optimal yield of the finished product. For example, at 16% extraction, some coffees have bright, clean, fruity flavors; at around 20%, they have a jammy, candy-like flavor. Someone once suggested that coffee flavors are at their best at 16% and 20% extraction, and that 17% to 18% is completely unusable. I don’t quite understand why the flavor drops between the two peaks, but let’s use the Manhattan cocktail as an analogy: dry and sweet are delicious, but the flavors in between are just average. Sometimes, we just like things that are either/or.

You can calculate the yield percentage of your coffee at home by first weighing the coffee before brewing (this should be done in accordance with standard operating procedures), then weighing the remaining coffee after brewing after drying it in a cold oven. Calculate the difference between the two samples and divide it by the original weight of the coffee to get the percentage value as a decimal. Of course, this method can take several hours and the operation process is not very accurate. If you have a deeper wallet, you can invest in a coffee refractometer (such as the one made by VST Labs). Refractometers use refracted light to measure the concentration of the brewed coffee liquid, and only need a 2 ml sample of cold coffee to display the reading digitally. You can also use a conversion table to calculate the TDS value of the coffee to determine the yield of soluble substances.

Brewing ratio

Another important factor to keep an eye on during brewing is the brew ratio. This value is the weight ratio of coffee liquid to coffee, which is used to indicate the strength of the finished coffee. The brew ratio for espresso is usually around 1.5:1, that is, 1 part coffee by weight is equivalent to 1.5 parts coffee liquid by weight, that is, 20 grams of coffee will make 30 grams of espresso. The standard ratio for French press brewing is about 15:1, that is, 20 grams of coffee will make 300 grams of drink. Because coffee will hinder the absorption of some water - 2 grams of water for every 1 gram of coffee, it is important to remember to use the total weight of the finished coffee, not the weight of the brewing water.

You may find it strange that what does the quality of coffee have to do with these numbers? How can it be bound by a few charts and formulas? Indeed, the human taste and smell system is ancient and excellent. 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 you 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 sentiment and scientific principles, it is a proposition of practical significance to control these variables to the best of your ability.