If you're a coffee drinker, you've probably heard a lot of rules about how to brew the perfect cup. Like, some people say that iced coffee is an abomination, or that you have to have the greatest Italian-made machine to make halfway decent java. It gets kind of hard to separate coffee fact from myth. Luckily, there's a whole stack of research that can help.
Scientific Points
- General Research on Coffee Brewing
- The article mentions "a whole stack of research" to help separate coffee fact from myth but doesn't specify particular studies.
- Study Comparing Caffeine in Arabica vs. Robusta
- Some studies are cited that compare caffeine content, stating that unroasted robusta beans have around twice the caffeine of arabica beans but less trigonelline.
- Study on Chlorogenic Acid Content
- It's noted that robusta has about 1.5 to two times more chlorogenic acid than arabica.
- 2014 Study on Water Quality
- A study from 2014 is referenced where researchers looked at how magnesium, sodium, and calcium bind to coffee compounds like caffeine, malic, citric, quinic, and chlorogenic acids, as well as eugenol.
- 2020 Study on Espresso
- A study from 2020 is mentioned where researchers created a mathematical model based on the Darcy-Forchheimer Law to determine the ideal espresso setup, discussing particle size and extraction.
How To Make The Best Coffee, According To Science
Brewing a beautiful cup of liquid gold may be an art form, but it's also very much a science. And we at TyN are here to fill you in on all that rich, balanced, and sometimes nutty research and show you how to make perfect coffee.
Before you start, choose your beans. Decide which coffee variety suits your taste. Do you know about coffee beans?
Luckily, this post discusses coffee from a scientific perspective. So, the scientific information below will help you choose the coffee you might like.
Science on Coffee Beans
It all starts with the coffee bean. with a Fun Fact:
Coffee beans are not actually beans; they are seeds! They come from the coffee plant, which is a member of the Rubiaceae family. The "beans" we use to make coffee are the seeds of the coffee cherry, a fruit that grows on this plant. When these seeds are roasted, they take on the familiar bean shape and develop the flavors and aromas we associate with coffee.
Sure, they might look bean-shaped, but beans are the seeds of legume plants, and coffee isn't a legume, so those little nuggets are just normal seeds.
But since nearly every English-speaking person calls them coffee beans, that's what we'll stick with in this post: Science on Coffee Beans.
Introduction
When people who aren't very knowledgeable about coffee go to choose coffee on the supermarket shelf, here's what they typically encounter:
- Brands and Packaging:
- Recognizable Brands: They might see familiar brand names like Folgers, Maxwell House, or Nescafé, which are often associated with reliability due to their widespread advertising.
- Packaging: Coffee is often packaged in bags, cans, or plastic containers. The packaging can be colorful and eye-catching, with images of coffee beans, cups of coffee, or landscapes evoking the origin of the coffee. Labels might highlight "100% Arabica" or "organic" to attract attention.
- Types of Coffee:
- Whole Beans vs. Ground: They'll see choices between whole bean coffee, which requires a grinder, and pre-ground coffee, which is ready to brew.
- Roast Levels: Terms like "light roast," "medium roast," and "dark roast" might be displayed, although the exact difference might not be clear to them. Dark roasts might be associated with stronger flavor due to the darker color.
- Blends vs. Single Origin: There might be blends, which are combinations of beans from various regions, or single-origin coffees, which come from one specific place, though the significance might not be immediately apparent.
- Flavors and Descriptions:
- Flavor Notes: Some packages might list flavor notes like "nutty," "chocolatey," or "fruity," but these might not influence the choice much if the consumer doesn't understand coffee flavor profiles.
- Marketing Terms: Words like "fair trade," "shade-grown," "organic," or "artisan" aim to appeal to consumers looking for ethical, environmental, or gourmet products.
- Price and Quantity:
- Price Points: Coffee can range from very affordable to premium-priced. Consumers might choose based on cost without understanding why one coffee costs more than another.
- Package Size: Coffee comes in various sizes, from small 8-ounce bags to large, family-sized canisters. The choice might be swayed by how much coffee they think they'll need.
- Specialty and Convenience Options:
- Pods or Capsules: For those with single-serve coffee makers, they might see pods or capsules, which simplify the brewing process but might not offer the freshest taste.
- Instant Coffee: This is often seen as a quick and easy option, though it might not be considered "real" coffee by enthusiasts.
- Best Before Dates:
- Freshness: Some might notice "best by" or "roasted on" dates, but without understanding the importance of freshness, this might not affect their decision.
For the average consumer, the choice often comes down to:
- Brand recognition
- Price
- Packaging aesthetics
- Convenience (ground vs. whole beans, instant vs. traditional)
- Any special claims or labels that catch their eye
They might not delve into the nuances of coffee like the bean's origin, roast profile, or brewing method implications unless they've started to develop a deeper interest in coffee.
So, lets talk about coffee, according to science.
Caffeine in Arabica and Robusta
If you have always known that coffee contains caffeine and makes it taste bitter, that is true. But the most scientifically correct is that the bitterness comes from alakoids.
Alkaloids in coffee, particularly in Arabica and Robusta varieties, are nitrogen-containing compounds that contribute significantly to the flavor and physiological effects of coffee. Here's a scientific overview:
Alkaloids in Coffee:
- Caffeine:
- Function: Caffeine is the most well-known alkaloid in coffee, acting as a natural pesticide for the plant and a stimulant for humans.
- Arabica: Generally contains less caffeine than Robusta. The caffeine content in Arabica can range from about 1.1% to 1.7% in dry weight of unroasted beans.
- Robusta: Contains higher levels of caffeine, typically around 2.2% to 4% in dry weight. This higher caffeine content is thought to be a defense mechanism against pests.
- Impact on Flavor: Caffeine contributes to the bitterness of coffee.
- Trigonelline:
- Function: Trigonelline is another significant alkaloid, contributing to the flavor profile of coffee, especially its bitterness. It also degrades into nicotinic acid (Vitamin B3) during roasting.
- Arabica: Has a higher content of trigonelline compared to Robusta.
- Robusta: While it has less trigonelline, it still contributes to the coffee's taste, particularly the bitter notes.
- Roasting Effect: Trigonelline partially breaks down into pyridines during roasting, which adds to the roasted, nutty flavors.
Scientific Insights:
- Extraction: Both caffeine and trigonelline are water-soluble alkaloids, meaning they are extracted into the brew when coffee is prepared. The extraction rate can be influenced by factors like brewing temperature, time, and the grind size of the coffee.
- Health Effects:
- Caffeine: Known for its stimulatory effects on the central nervous system, increasing alertness, and potentially affecting metabolism and cardiovascular system.
- Trigonelline: Has been studied for potential health benefits, including antioxidant properties, although its effects are less pronounced than caffeine's.
- Genetic Factors: The genetics of coffee plants influence the alkaloid content. Arabica, being a tetraploid species (resulting from the hybridization of two diploid species), has a different genetic makeup than Robusta, which affects the synthesis of these compounds.
- Environmental Influence: The growing conditions, including altitude, climate, soil, and processing methods (like wet or dry processing), can also impact the alkaloid profile of coffee beans.
- Research: Studies into coffee alkaloids focus on their biosynthesis, genetic regulation, and the impact of agricultural practices on their concentration. For example, research might explore how different roasting profiles can modulate the release of these compounds, affecting both flavor and health implications.
Analytical Techniques:
- Quantification: Methods like HPLC (High-Performance Liquid Chromatography) are used to quantify caffeine and trigonelline in coffee samples to understand variations across different coffee species, origins, and processing methods.
- Sensory Impact: Sensory science also examines how these alkaloids contribute to the sensory profile of coffee, linking chemical composition to taste perception.
In summary, alkaloids like caffeine and trigonelline differ between Arabica and Robusta in terms of concentration, which influences the coffee's taste, aroma, and physiological effects.
Understanding these compounds from a scientific perspective helps in appreciating how coffee's chemistry shapes its consumption experience.
Acid Content
The second main group of compounds in coffee, after alkaloids, are indeed acids, which play a crucial role in defining the flavor profile of coffee. These acids contribute to the coffee's taste, particularly its sourness, acidity, and sometimes bitterness. Here's an explanation of these key acids:
Major Acids in Coffee:
- Chlorogenic Acids (CGAs):
- Formation: Chlorogenic acids are esters of caffeic and quinic acids, found in significant amounts in green coffee beans.
- Contribution to Taste: They are responsible for the coffee’s astringency and can impart a bitter taste. During roasting, CGAs degrade into various compounds, some of which contribute to the development of bitterness and sourness.
- Health Aspects: CGAs are antioxidants, and there's ongoing research into their health benefits, including potential effects on blood pressure, glucose metabolism, and anti-inflammatory properties.
- Quinic Acid:
- Role: Quinic acid forms part of chlorogenic acids but also exists independently in coffee. It contributes to the sour taste of coffee, especially in lighter roasts where less degradation has occurred.
- Transformation During Roasting: Quinic acid levels increase during roasting as chlorogenic acids break down, influencing the coffee's acidity.
- Caffeic Acid:
- Source: Another component of chlorogenic acids, caffeic acid can also be present in free form.
- Taste: It contributes to both sourness and bitterness, depending on the concentration and transformation during roasting.
Other Notable Acids:
- Citric Acid: Adds to the bright, tart flavors often found in African coffees or light roast profiles.
- Malic Acid: Contributes to a fruitier, apple-like acidity, enhancing the complexity of the coffee's flavor.
- Acetic Acid: More common in over-fermented or improperly stored beans, it can impart a vinegar-like taste, though in small amounts, it might contribute to the coffee's acidity profile positively.
Influence on Coffee:
- Acidity vs. pH: The term "acidity" in coffee refers to taste rather than pH. Coffees can be described as having high acidity (bright, citrusy, tart), even if their pH isn't particularly low. The perception of acidity in coffee is more about the balance and type of acids present rather than actual pH levels.
- Roast Level Impact:
- Light Roasts: Retain more of these acids, leading to coffees with higher perceived acidity and a more vibrant, sometimes tart, flavor.
- Dark Roasts: Much of the acid content degrades or transforms, reducing the perceived acidity and increasing bitterness from other compounds formed during roasting.
- Processing and Origin: The way coffee cherries are processed (washed, natural, honey-processed) can significantly affect the acid profile. For instance, washed coffees tend to be more acidic than natural processed ones. The origin also influences acidity, with regions like Ethiopia or Kenya known for their bright, acidic coffees.
- Brewing Methods: The method of brewing impacts acid extraction. For example, cold brew coffee is generally less acidic because fewer acids are extracted at lower temperatures over longer times.
Understanding these acids helps in appreciating how the chemical composition of coffee translates into flavor, acidity, and overall taste experience. It's a key aspect for both coffee professionals and enthusiasts in tailoring coffee to personal taste preferences or in understanding why a particular coffee might taste the way it does.
Robusta has around 1.5 to two times more chlorogenic acid than arabica on average, so as well as being more bitter, it's a little more astringent too.
Then there's sucrose or sugar, which, unsurprisingly, gives coffee its sweet notes, but also breaks down during roasting to more sweet-tasting compounds.
Sweet Notes in Coffee:
- Sucrose and Other Sugars: The sweetness in coffee largely comes from sugars like sucrose, which are present in the green coffee bean and undergo caramelization or participate in the Maillard reaction during roasting. This creates sweet, caramel-like, or even fruity notes.
- Maillard Reaction Products: While chlorogenic acids degrade, other compounds formed through the Maillard reaction (like melanoidins) can contribute to the perception of sweetness by balancing out or masking bitterness and acidity.
- Furans: These compounds, formed during roasting, can contribute to malty or sweet flavors, enhancing the perception of sweetness.
Raw arabica beans have more sucrose than robusta, which gives arabica caramel, fruity, or fermented aromas when it breaks down.
Furan Content
Furan is an aromatic heterocyclic organic compound that's of interest in food chemistry, particularly concerning coffee. Here's what you need to know about furan in relation to coffee:
Formation in Coffee:
- Roasting Process: Furan is generated during the roasting of coffee beans. It's formed from the thermal degradation of carbohydrates, amino acids, ascorbic acid, unsaturated fatty acids, and carotenoids. This process is similar to the Maillard reaction, which also gives coffee much of its flavor and aroma.
- Bean Type: Both Arabica and Robusta beans produce furan during roasting, but the levels can vary. Arabica, being typically roasted at lower temperatures or for less time, might produce less furan than Robusta, which is often roasted at higher temperatures or for longer periods.
Health Concerns:
- Toxicity: Furan is classified by the International Agency for Research on Cancer (IARC) as "possibly carcinogenic to humans" (Group 2B). This classification is due to evidence of furan causing liver tumors in animal studies. However, the direct impact on human health, especially at the levels typically found in food, is still under investigation.
- Regulation: Due to health concerns, there are ongoing discussions and research about regulating furan levels in foods, including coffee.
Levels in Coffee:
- Concentration: Furan levels in brewed coffee are generally lower than in roasted or ground coffee due to evaporation during brewing. However, the concentration can still be significant:
- In roasted whole beans or ground coffee, furan levels can approach thousands of micrograms per kilogram (μg/kg).
- In brewed coffee, levels are typically below 120 micrograms per liter (μg/L), but this can vary with roast degree, brewing method, and how fresh the coffee is.
- Variation: The amount of furan can vary based on:
- Roast level: Darker roasts generally contain more furan due to the higher temperatures and longer roasting times.
- Brewing method: Methods that involve more heat or longer contact times with the beans might result in higher furan in the brew.
- Age of coffee: Freshly roasted coffee has higher furan content, which decreases over time.
Mitigation:
- Roasting Techniques: Some research suggests that adjusting roasting conditions might help reduce furan formation without compromising flavor too much.
- Brewing Practices: Using brewing methods that minimize heat exposure or using coffee that has aged slightly might reduce furan intake, though this also means less of some desirable flavors.
Research and Regulation:
- Ongoing Studies: There's a lot of research into how furan forms, how it can be minimized, and its health impacts at dietary exposure levels. This includes looking at how furan levels change from bean to cup and through various preparation methods.
- Public Health: Public health bodies and food safety agencies monitor furan levels in coffee and other foods to assess risk and potentially guide regulations or recommendations for consumers.
For those concerned about furan exposure, while enjoying coffee:
- Moderation: Like with many things, moderation is key. Coffee is a common source of dietary furan, but the levels are generally within safety margins for most people.
- Variety: Experimenting with lighter roasts or different brewing methods might not only change your coffee experience but could also influence furan content.
So picking the perfect bean for the flavor profile you want in your final cup is pretty vital, even though you might not be thinking about furans or acid while you're in the coffee aisle.
Keep me Awake, Coffee!
Ok, but maybe you're less concerned about flavor notes and bouquets, and more interested in getting the maximum amount of caffeine as quickly as possible.
You've got a deadline! So as you frantically Google how to jam as much caffeine into your system as possible, you may have read that lighter roasts pack more of a caffeine punch than darker ones.
I'm sorry to tell you that this is a bit of a myth, and here's why.
A lighter roast of coffee literally just means it was roasted for less time or at lower temperatures. And, while some compounds in those beans break down during roasting, caffeine isn't one of them. But even though caffeine doesn't break down, it can be released during roasting as the pores of the coffee beans close up, gas builds up inside, and the beans eventually crack open.
However, different studies have assessed the level of caffeine depending on the roast level, and most have pretty much found no significant difference. But there can still be a bit of truth to this myth, depending on how you're measuring out your beans for that cup of joe.
The beans lose mass as they roast, but they also grow in volume. That means darker roasts get lighter and take up more space than the lightly roasted ones.
So if you're comparing light versus dark roast scoop for scoop, you're probably measuring out fewer beans and therefore potentially less caffeine.
Despite all that, the differences between a dark and light roast are probably so small, you wouldn't notice when drinking it.
Science on Brewing Time
Alright, you've picked your beans and ground them, and now it's time to brew.
In scientific speak, many of the properties of coffee like smell, flavor, and texture, come down to chemical and physical kinetics; how chemicals react and how things move.
You might not immediately think of coffee as something that's moving, but brewing coffee is all about hot water moving over or around coffee grounds, either because it's forced with pressure or thanks to gravity.
There are a couple of ways this can happen. There are infusion methods, like pour-over, where water flows over the coffee grounds and those grounds soak in water, usually hot, for a short time before being filtered, all with the help of gravity to pull the brew through.
Infusion methods usually result in a milder, less harsh cup of coffee and are well-suited to bringing out lighter, fruitier flavors. Decoction methods, like percolator coffee, boil the grounds in hot water before condensing the coffee vapors back into a liquid. Those high temperatures of a decoction method mean the coffee compounds are sucked out of the grinds really quickly, but there's also not a lot of contact time between the grinds and the water, so you end up losing some flavor and ending up with a very strong cup of pretty bitter coffee.
Then you've got pressure methods, like espresso, where you force hot water over tightly compacted grounds. Yes, espresso is a method of making coffee, not a specific kind of bean! Although you may see bags on the store shelves labeled "espresso", it's not actually espresso unless it's brewed into, well, espresso.
The combination of slightly different particle sizes in espresso grinds means those grinds get packed together when you press down on them before popping them into the machine. And that makes the mix better at withstanding pressure during brewing.
Then, if there's good resistance to the pressure, the energy from the hot water is transferred to the coffee grind block, extracting more oils with the water, and giving the deep flavor and creamy texture of espresso. So picking out your method of coffee concocting matters a lot!
How Water Quality Bind Caffeine.
If you really want to dial in particular coffee flavors, you might want to take a hard look at your water source, too. Hard water is full of positive ions, like magnesium and calcium ions, that can grab onto flavorful compounds. And funny enough, those ions might just make your final brew that much better. See, each of those molecules that gives coffee its flavor, whether it's caffeine or one of the acids, have some negatively-charged electrons around. The positively-charged ions in hard water get attracted to these negative parts of the coffee compounds, which helps pull them into the water.
In a 2014 study, researchers looked at how well magnesium, sodium, and calcium bind to the coffee compounds like caffeine, malic, citric, quinic, and chlorogenic acids as well as a spicy clove-flavored compound called eugenol. They found that magnesium bound most strongly and closely to all the compounds, followed by calcium. Sodium didn't really cling onto any of the compounds any more than water molecules did. So according to this study at least, opt for magnesium-rich water if you want to get the maximum flavor out of your beans. But there's a catch. You also need to make sure that water has enough bicarbonate in it to keep the acidic components in check. So yea, that one coffee shop bro boasting about how they triple osmosis filter their water might be doing more to make even less flavorful coffee.
So now that you've picked out your bag of beans at the store, you may be staring at that giant coffee grinder thing, trying to figure out what setting to go for. Or maybe you took an espresso class and they told you to take a whole lot of beans and grind them up super finely. That advice makes sense, since there's lots of surface area for the water to pull all those yummy coffee compounds from. But pulverizing your coffee into literal dust might not be the way to go. At least according to mathematics.
Espresso: Setup, Grind size, Extraction.
The Darcy-Forchheimer Law, named after the engineers that developed it, was originally designed to explain how water flows through a column of sand. But it works just as well for coffee! It predicts how water is going to flow over those coffee grounds, depending on things like the gradient the water's moving along, and the area the water's moving through. And that can tell you something about how strong or flavorful the brew might be. If the particles are too fine, the water can't get through, and that coffee spends ages having the juice sucked out of it, making it bitter or over-extracted. Too coarse though, and the hot water just flows right over the grounds, under-extracting the flavors and leaving you with a sour coffee.
In a study from 2020, researchers created and tested a mathematical model, based partly on the Darcy-Forchheimer Law, to dial in the perfect espresso setup. When they ground the beans too fine, they ended up with uneven regions of pressure building up on that little mound of coffee. That meant only some of the coffee was properly extracted, and they ended up with coffees that were different from one cup to the next. So unlike the typical barista lore, they found that using less coffee (15 grams instead of the usual 20) and grinding it more coarsely consistently gave them much better tasting brews. And just like science in general, reproducibility is what you want when it comes to your morning cup. Plus, by using less beans, you end up with more cups of coffee from your bag and less waste! Win, win!
Now, we all know that one curmudgeonly person who insists on ordering their latte extra hot. Or the one purist who says iced coffee is an abomination to the coffee art form. Although neither is really 100% right, temperature does play a pretty big role in how that final cup tastes. The National Coffee Association recommends a temperature of between 90 and 96 degrees Celsius, or 195 and 205 Fahrenheit, just under boiling temperature. That's because the temperature of the water dictates how fast all those flavor compounds seep out of the grind.
See, as temperature increases, the water molecules gain energy and interact more with the coffee grounds. More interaction means more extraction! Now, some coffee flavor compounds that are really soluble in water get sucked out of the coffee quickly, regardless of temperature. These include the quinic, malic, and citric acids. But there are also compounds that dissolve differently in water at different temperatures. These are mostly the compounds that give coffee its bitter taste, like the alkaloids we talked about earlier. So with hotter water, you get more of these bitter compounds leaching out. Extra hot water can also let out other compounds like pyrazines, which give an earthy or burnt taste. Which is probably why people often report that coffee brewed at hotter temperatures can taste pretty bitter.
But scalded coffee is also described as sour, which doesn't immediately make sense since the sour compounds come out regardless of temperature. Coffee scientists, who basically have my dream job, think that bitter and sour compounds have an additive effect. So if more bitter compounds like caffeine get into the water at hotter temps, then this makes the sour compounds taste more sour.
Now, you might be wondering about cold brew. In cold brewing, it's time doing all the work, not temperature. The cool water slooooowly sucks those flavor compounds out of the grounds. And some compounds, including the chlorogenic acids and trigonelline, leach out much more slowly. So depending on how long you steep the coffee for, cold brew is generally sweeter and less acidic.
And now that you've got your brewer, your beans, and a whole bunch of science knowledge, you're ready to go and make your coffee. All this said, the perfect cup of coffee is the one you like the best. If you're looking to improve your brewing game, feel free to bring what you've learned here into the kitchen. But if your coffee hits the spot, there's no science that can tell you you're wrong! And this one is pretty darn good.
Scientific sources related to the five points mentioned:
Source:
- Research on Coffee Brewing
- Title: "Coffee extraction: A review of parameters and their influence on the physicochemical characteristics and flavour of coffee brews"
- Source: ScienceDirect
- This study reviews various parameters influencing coffee extraction and how they affect the physicochemical and flavor characteristics of coffee.
- Comparison of Caffeine in Coffee
- Title: "Caffeine content in coffee as influenced by grinding and brewing techniques"
- Source: ScienceDirect
- This research explores how different preparation methods influence caffeine content in coffee.
- Chlorogenic Acid Content
- Title: "Espresso coffees, caffeine and chlorogenic acid intake: potential health implications".
- Source: PubMed
- This study looks at the variability in chlorogenic acid and caffeine content in commercial espresso coffees, highlighting health implications.
- Effect of Water Quality on Coffee
- Title: "The Influence of Water Composition on the Extraction of Coffee Compounds"
- Source: Journal of Agricultural and Food Chemistry *
- This study (from 2014, as mentioned) investigates how different ions in water affect the extraction of coffee compounds, including caffeine and various acids.
- Study on Espresso on Setting, Particle Size, and Extraction
- Title: "Influence of Particle Size Distribution on Espresso Coffee Quality"
- Source: Food Research International *
- Title: "What kind of coffee do you drink? An investigation on effects of eight different extraction methods".
- Source: PubMed
- This study examines the effects of different extraction methods, including particle size, on coffee quality, which indirectly relates to espresso brewing.
- Thumbnails Illustration:
- Kawai Coffee Cup by Noongraphicstudio | source Istockphoto
- Coffee Beans background: Generated with AI
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