How Hand-Brewed Coffee Acidity is Determined: Factors That Influence Coffee Acidity

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Introduction

The development of specialty coffee has given people a deeper understanding of coffee. Coffee is not just bitter—it also has acidity and sweetness. Different regions produce different regional flavors, such as the delicate floral notes of Panama washed Geisha, the citrus fruits of washed Yirgacheffe, the herbal spices of wet-hulled Mandheling, and the acidic berries of washed Kenya...

Among these, acidity is an important component of coffee flavor. Whether in SCA's cupping form or COE's cupping form, acidity is an important scoring criterion for judging coffee quality and flavor expression.

So what affects the acidity in coffee? And how should we adjust the acidity in pour-over coffee?

What Affects Acidity in Coffee?

First, we need to understand where acidity in coffee comes from and what affects it. Coffee is essentially a plant, a crop, a fruit. Mature coffee cherries are red on the outside and taste sweet and sour, so coffee itself has acidity. The acidity in coffee comes from its contained citric acid, malic acid, chlorogenic acid, etc.

The acidity of coffee is one of its charms, but at the same time, the acidity in coffee can also provide us with much information. The acidity in coffee is affected by the altitude of the growing region. In the world of coffee, altitude is perhaps one of the most important indicators of coffee quality. The higher the altitude, the better the quality of coffee beans. FrontStreet Coffee also firmly believes that, under consistent conditions, the higher the altitude, the more likely you are to find high-quality coffee beans. Why? Because high altitude brings huge temperature differences between day and night. Coffee trees grow slowly under these conditions, giving them enough time to accumulate nutrients, which are precursors for developing refined flavors. High-altitude coffee beans often carry bright, refined acidity that makes the mouth water.

Secondly, the coffee variety affects acidity. Taking Arabica and Robusta as examples, the difference between them is that Robusta has higher caffeine and chlorogenic acid content. Chlorogenic acid is an unpleasant acid that feels astringent and harsh. Through roasting, chlorogenic acid degrades into quinic acid, which is a phenolic acid, non-volatile, so it cannot be detected by smell, but it tastes bitter and is one source of the bitter taste in dark-roasted coffee. Another representative example is Kenya's SL28 and SL34—two laboratory varieties that adapted to Kenya's high-phosphorus soil and produced strong acidity.

From growing conditions to coffee varieties, the processing methods we're familiar with also affect coffee acidity. FrontStreet Coffee often shares that washed coffee has higher acidity while being very clean, while natural coffee is fuller and more complex, and the wet-hulled method accidentally created the low-acidity, full-bodied character of Indonesian coffee.

Finally, coffee beans are exported to various importing countries, where professionals in different cafés roast the raw coffee beans and perform the final brewing. Roasting is the last factor that determines the basic flavor profile of coffee. The darker the roast, the lower the acidity, and vice versa. The final brewing also leads to different taste experiences in coffee.

How to Adjust Acidity in Pour-Over Coffee?

In the process of brewing coffee, how we extract also leads to different coffee flavors. First, we need to understand how coffee flavor is extracted. The entire extraction process of coffee, or brewing process, extracts acidity first, then sweetness, and finally bitterness. If you try the front, middle, and back stages of the brewing process, you'll find that the front stage is more concentrated with higher acidity, the middle stage begins to decrease in concentration with the most obvious sweetness, and the back stage is lighter with lower concentration, where you mostly taste bitterness or woody flavors.

That's why people often say the purpose of extracting the back stage is to adjust the concentration of the entire cup of coffee, while the extraction that mainly affects coffee flavor is in the front and middle stages. At this level, we know that to adjust the acidity of pour-over coffee, we can adjust the extraction of the front and middle stages. If I want to extract more acidity, I can increase the extraction of the front stage, for example, by adding an extra stage in the front or increasing turbulence during water pouring.

Taking FrontStreet Coffee's brewing as an example: 15 grams of coffee powder to extract 225 grams of coffee liquid, divided into three pour stages. The first stage injects 30 grams for blooming, the second stage to 125 grams, and the third stage injected to 225 grams. As just mentioned, if you want more pronounced acidity, one method is to split the second pour into two stages, turning three pours into four pours. The second method is to increase turbulence in the second stage, increasing the extraction of the front and middle stages through greater turbulence.

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