What's the Fundamental Logic of Pour-Over Coffee? How Should Grind Size and Water Temperature Be Set? What Impact Does Water Quality Have on Coffee Extraction?

The Timeless Appeal of Pour-Over Coffee

Today, pour-over coffee remains a beloved favorite among coffee enthusiasts. Its brewing method is simple and convenient, while effectively highlighting the natural flavors of coffee itself! Moreover, the brewing process is incredibly therapeutic, providing both physical and mental relaxation. This is why so many people continue to fall in love with pour-over coffee, becoming devoted enthusiasts one after another.

Understanding the Fundamentals of Coffee Extraction

As FrontStreet Coffee mentioned, understanding the fundamental logic of coffee brewing is more important than the brewing method itself! All brewing methods are formulas derived around extraction logic. Therefore, once you master extraction theory, even as a complete beginner, you can quickly learn to brew an excellent cup of pour-over coffee! Additionally, you'll be able to analyze the operating principles of different brewing methods. So first, we need to understand: what exactly are we extracting when making pour-over coffee?

What Are We Extracting in Pour-Over Coffee?

Actually, this isn't just about pour-over coffee—all coffee extraction follows the same principle. We know that in a coffee bean, there are 30% soluble substances and 70% insoluble substances. Insoluble substances mainly refer to the woody fibers of coffee, while soluble substances include caffeine, proteins, sugars, carbohydrates, various acids, fats, and more. The three primary flavors of coffee—acidity, sweetness, and bitterness—are all contained within these soluble substances. What we need to do when extracting coffee is to draw out these flavors.

The proportions of acidity, sweetness, and bitterness in coffee beans are primarily influenced by the degree of roast. Lighter roasts contain higher acidity content, while darker roasts contain higher bitterness content. Since flavors interact with and balance each other, different proportions of these flavors result in different characteristics in the final brewed coffee. Therefore, to achieve a delicious, ideal cup of coffee, what we need to do during extraction is to reasonably and appropriately extract these three flavors from the coffee beans!

The dissolution rates of acidity, sweetness, and bitterness differ significantly. Acidic substances dissolve fastest and are quickly extracted in large quantities when washed by hot water. Bitter substances dissolve slowest, and when the acidic and sweet substances have been fully extracted, only bitterness continues to be released due to its slow dissolution rate. It's important to note that bitterness is the flavor most easily perceived by human taste buds. When present in small amounts in coffee, it can enhance overall body and richness. However, when bitterness accounts for too high a proportion in coffee, it will mask other flavors. Therefore, we need to control the dissolution rate, allowing only a small amount of bitterness to be released without overwhelming other flavors (it should be present, but not excessive).

The Golden Cup Standard and Water as Extraction Medium

However, since we cannot detect the amount of substances being released, we cannot determine at which stage the peak bitterness release occurs. In situations like this, we can turn to the Golden Cup concept! Research on the Golden Cup standard shows that coffee with extraction rates between 18% and 22% is most popular. This is because bitterness is generally unappealing to most people and is primarily released in the later stages. In other words, the reason coffee with extraction rates exceeding 22% is unappealing is because excessive bitterness is released. As long as we control the extraction rate within this range, we can avoid the release of excessive bitterness and thus achieve a delicious cup of coffee! (However, the Golden Cup extraction is not absolute—don't apply it to all coffees; taste should still be the primary judge.)

But to extract these substances, we inevitably need an extraction medium, and this is where water plays its role. It helps dissolve the soluble substances from coffee! In our daily lives, seemingly colorless and odorless water actually contains minerals (in most cases), and the amount of these substances determines the hardness of water, which can also affect the flavor profile of coffee. However, this factor is not as important as others, so we can skip it for now. Friends who want to learn more can refer to the article "What Water Makes Better Tasting Coffee?" What we need to understand more is how to use water to properly extract substances from coffee!

Controlling Extraction Through Brewing Parameters

Extracting substances from coffee isn't difficult, but the challenge lies in extracting the appropriate amount. Therefore, we need to control the dissolution rate of coffee substances by creating brewing plans! In brewing plans, there are four main visualizable factors: coffee-to-water ratio, grind size, water temperature, and brewing time. Although each factor exists independently, if we want to extract a reasonable amount of substances from coffee, these four factors must interact with each other, finding their own reasonable balance points based on the efficiency of other factors. This is what we call: controlling dissolution efficiency. So let's understand how these factors control dissolution efficiency!

Water Temperature

As the solvent in the extraction process, water temperature determines the degree of molecular movement! The higher the temperature, the more intense the molecular movement—in other words, stronger extraction efficiency. Extraction efficiency determines the extraction speed of coffee substances. With other parameters consistent, higher water temperature results in faster extraction of substances. Generally, we need to determine water temperature based on the roast degree of the coffee beans! Lighter roasted beans require higher temperatures for extraction because their shorter roasting time results in higher density, so hot water needs higher temperatures to dissolve substances from the coffee. Darker roasted beans have lower density, and excessively high water temperature can easily lead to extraction of substances that shouldn't be dissolved, so we need to lower the temperature to reduce the release rate of negative substances. (FrontStreet Coffee uses water temperatures of 91-93°C for light roasts and 87-89°C for dark roasts)

Coffee Grind Size

The grind size of coffee determines the surface area that water can contact. The finer the grind, the larger the surface area that water can contact! Additionally, the distance from the exterior to the center of the coffee particles is shorter, allowing water to reach the interior of the coffee grounds in less time, thereby achieving faster extraction.

Of course, finer isn't always better with grinding! Just like water temperature, different roast degrees require different suitable grind sizes. Moreover, when coffee is ground, it produces very fine particles (fines). The finer the grind, the more fine particles are produced. Because their extraction efficiency differs from larger particles, an appropriate amount of fines can add certain complexity to coffee. However! If there are too many fine particles, not only will they fail to contribute positively to the coffee, but during brewing, these fines can also easily clog the filter paper's pores, extending the coffee's extraction time and leading to over-extraction. (FrontStreet Coffee uses grinds with 80% pass-through rate on a #20 sieve for light roasts and 75% pass-through rate for dark roasts)

Coffee-to-Water Ratio

The coffee-to-water ratio refers to the proportion of coffee grounds to water volume when making coffee. It primarily controls the concentration of a cup of coffee. When extraction rates are the same, a higher ratio results in higher coffee concentration, and vice versa.

Similarly, the coffee-to-water ratio is influenced by other parameters and brewing methods! We need to adjust the ratio based on our taste preferences or brewing methods. (FrontStreet Coffee typically uses a coffee-to-water ratio of 1:15)

Brewing Time

The process of brewing coffee requires time. The period from when hot water first contacts the coffee grounds until the last drop of coffee liquid leaves the filter cup is our brewing time!

The longer the brewing time, the longer the contact time between hot water and coffee grounds, resulting in higher extraction efficiency. The shorter the brewing time, the lower the extraction efficiency with the same parameters. The brewing time is mainly affected by water percolation speed, and many factors can influence this aspect. For example, grind size! The finer the grind, the smaller the gaps between coffee particles, the slower water can percolate, thus extending the time. Or the coffee-to-water ratio! The smaller the ratio, the more hot water is poured, and time will increase with the amount of water. Additionally, there's the filter paper and filter cup! The thickness and material of the filter paper, as well as the flow-through design of the filter cup, all affect percolation speed. (Based on the above parameters, FrontStreet Coffee controls brewing time within 2 minutes ± 5 seconds)

The Impact of Water Flow

Then, besides the aforementioned adjustable parameters, there's another factor that affects coffee extraction efficiency: water flow!

When brewing, we often use circular motions to pour hot water. At the same time, we continuously adjust the height of the pouring position. The main purpose of these two operations is to agitate the coffee grounds (stirring) through the impact force of the water flow, thereby achieving higher extraction efficiency!

FrontStreet Coffee offers another familiar example: Banlangen (isatis root) granules. We can compare two cups of Banlangen preparation: same hot water, same dosage, with the only difference being that one cup is stirred while the other is not. We would then find that the unstirred cup of Banlangen granules definitely dissolves slower than the vigorously stirred one. This is the kinetic energy brought by water flow impact! The stronger the impact force of the poured water flow, the more intensely the coffee grounds will agitate, and soluble substances will be dissolved more quickly. For details, you can refer to the article "The Impact of Water Flow on Coffee."

Conclusion: The Path to Consistent Excellence

Above are the important factors that affect coffee extraction. Like flavors, they interact with and constrain each other! When the extraction efficiency of one factor in an extraction formula changes, to extract equally delicious coffee, other factors must change together to correct the extraction efficiency! Most of the brewing methods we know are born by changing the extraction efficiency at certain stages. Of course, there are many other factors that can affect brewing that haven't been mentioned, but FrontStreet Coffee believes that for beginners, it's necessary to first familiarize themselves with and master the basic factors mentioned above before they can better absorb other knowledge.

Then we need to know that if we want to continuously brew delicious coffee, visualizing data is very important. Digital scales for weighing, timers for timing, sieves for measuring grind size, and thermometers for measuring water temperature are all tools that can visualize data. When brewing, we only need to record the current brewing parameters well, and then we can freely modify or replicate this cup of coffee we're brewing!

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