Some people care nothing for coffee brewing science; they stumble out of bed in the morning, still drowsy, to make what they call a cup of coffee. Never let a languid person make you coffee!
You may have noticed that coffee from a single jar of grounds tastes differently, depending on who brews it and how it’s prepared. It’s because the richness of a cup of coffee depends a lot on the skill of the brewer and their understanding of the underlying science.
This article will demystify coffee brewing science through the lens of chemistry. It will explain how factors like water chemistry, extraction time, temperature, and coffee grind size influence the quality of the final brew. Let’s see how this applies.
Extraction: The Heart of Coffee Chemistry
Coffee extraction chemistry focuses on the interplay between hot water and coffee grounds during the brewing process. Coffee extraction science commences right after the hot water comes into contact with the beverage. At this point, the soluble compounds in the grounds leach out into the hot water. Therefore, the water serves as a solvent to extract the flavorful vitality that is characteristic of high-quality coffee.
When a barista adjusts coffee brewing variables, the goal is to create the optimal conditions for extracting specific coffee components. The variables in question that are likely to affect the quality of a coffee brew are listed below:
- Water quality
- Extraction time
- Temperature
- Grind size
These factors are not peculiar to perfect coffee brew methods alone. Instead, it applies to any beverage that involves the decoction or extraction of flavorful essence. For example, a brief lesson on how to brew the perfect cup of tea will reveal that the process exploits the same variables.
Carefully manipulating the coffee brewing variables will determine how much aromatic oils, carbohydrates, sugars, acids, caffeine and bitter alkaloids get extracted. Subsequent sections will discuss how each of the mentioned variables affects brew chemistry.
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The Role of Grind Size in Coffee Brewing Science
Coffee bean grinding, like brewing, is a science and simultaneously an art. Coffee extraction science depends significantly on grind size, as it determines the rate and effectiveness of compound extraction. Fine coffee grinds, with a particle size similar to table salt, have a large surface area. The smaller the particle size, the larger the coffee grinds’ surface area, making the extraction of desirable compounds relatively faster. Conversely, Larger coffee grinds, with consistencies similar to granulated sugar, require more solvent dwell time for the extraction of desirable compounds.
Coffee grind size and taste also enjoy an inseparable relationship. For some context, fine grinds are suitable for preparing a rich and full-bodied cup. Espresso preparation often involves fine coffee grinds. The only drawback of using fine grinds is that over-extraction may occur during brewing. Over-extraction of coffee grinds causes undesirable characteristics like astringency and bitter taste. On the contrary, coarse coffee grinds are susceptible to under-extraction. This is because some of the coffee essence may remain unextracted.
Coffee extraction science is not dependent on the grind size effect alone. The temperature of the water, or milk, and its dwell time on the grind, are also pivotal to coffee brewing science.
Water Temperature and Contact Time
Water brewing temperature influences the brewing process because it affects the extraction of soluble compounds. Most industry experts recommend 195°F and 205°F (90°C to 96°C) as the range for perfect coffee temperature.
You don’t want the water for coffee brewing too hot or too cold. Using water above 205°F (96°C) can cause over-extraction of coffee essence and a bitter or harsh taste. Similarly, brewing coffee with water below 195°F (90°C) will cause under-extraction. An under-extracted brew is weak in flavor compounds and sometimes sour-tasting.
Interestingly, water temperature coffee brewing cannot be considered in isolation. The contact time of the hot water with the coffee grounds also influences the quality of the brew. Baristas who have mastered the art of coffee brewing know how to strike just the right balance between water temperature and contact time.
Water Chemistry and Coffee Brewing Science
Coffee brew chemistry has a strict water requirement for a full-bodied beverage. The water should have a near-neutral pH (not acidic or basic). Slightly hard water is ideal for coffee brewing. Dissolved minerals like magnesium and calcium confer desirable flavor effects on the brew. Before you ask what in the world hard water is, don’t take that for its literal meaning. Hard water contains dissolved minerals, and as you must have guessed, soft water has negligible mineral content. When mixed with food items that contain materials that react easily with the minerals, a sludge may form. When water for brewing is excessively hard, it may form sludgy deposits in your coffee machine.
The Specialty Coffee Association of America (SCAA) has recommendations about water standards required for an optimal brew. It involves water properties like alkalinity, pH, hardness and total dissolved solids (TDS) staying within specified thresholds. Chlorine content, odor and color are non-negotiable for coffee brewing water. The water should contain no chlorine, be colorless, and odorless.
Brewing Methods and Their Chemical Profiles
There’s no such thing as a perfect coffee brew method. Coffee brewing science involves five broad methods, and the ultimate choice depends on how you want your cup of coffee to turn out. Below is a brief snippet of each brewing method.
1. Cold Brew
Because this brew is done at low temperatures, the flavor compounds in the coffee grounds take a long time to adequately extract. So, a cold brew could take as long as 12 or even 24 hours. There’s no special training required for this brewing process, just the right equipment and enough patience to see the extraction through.
The resulting coffee is usually smooth, low-acid and suitable for iced coffee. However, it can be quite messy to strain the spent coffee grounds.
2. Espresso
This brewing method involves the use of pressurized extraction. So, it’s usually very fast. It requires an espresso machine to induce the pressurized conditions earlier described, and these machines can come with hefty price tags.
Unfortunately, your expensive espresso machine is not a guarantee for nailing a quality brew. So, some training is required for this brewing method. However, once you nail the art, cupping consistent top-quality, bold and creamy brews becomes a breeze.
3. AeroPress
AeroPress’ coffee brewing science is more like an improvement on the French Press. The qualities of brews from these two methods are fairly the same, except for the acid content and brew time. In about two minutes, an AeroPress produces a clean and smooth, but concentrated, brew.
Also, AeroPresses have multiple brew configurations, making them clean and very easy to use. The only drawback of this method is its significantly small brew capacity.
4. Pour-Over
The pour-over method permits considerable versatility among the many brew variables. You can adjust the contact time and water temperature to suit your purpose. Due to the human expertise required for this method, it may take a long time to master. So, if you’re new to coffee brewing, you may want to try out easier methods first.
5. French Press
This method allows about the longest dwell time of coffee grounds in hot water because it involves immersion. If you want your coffee strong and full-bodied, with all the flavors the grounds have to offer, use the French press method.
The use of a glass carafe for this brew method can sometimes make the process messy. Understanding the grind size effects of coffee quality also plays a significant role in this brew method.
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7 Practical Tips for Home Brewers
Whether you have developed a distaste for commercial coffee, making yours at home may be the way to go. It may even be a case of whipping up enthusiasm for gourmet coffee and entertaining home guests with your brewing skills. Whichever one applies to you, we have a couple of tips to help you make better cups of coffee at home.
- Clean your coffee machine more often. Edible cleaning agents like vinegar can help remove those stains.
- After perfecting a brewing method, occasionally try out new ones to improve your craft.
- Buy and grind your coffee beans; your brew quality is likely to improve.
- Brew your coffee within two weeks of roasting and grinding, and you get more of the flavor that way.
- Never neglect your water quality.
- Want your coffee to stay warm for longer? Preheat the mug before dispensing the beverage.
- Keep a scale handy to measure the correct grounds-water proportion.
It needs no saying that knowledge of coffee brewing science may be futile without an understanding of the art. Drive yourself to explore new coffee flavors, and if you’re a home brewer, new methods.
When you master the chemistry, every coffee cup becomes a masterpiece.
