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Who Makes The
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Coffee Answers

EVERYTHING YOU EVER WANTED TO KNOW ABOUT COFFEE.

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Six coffee questions, answered without the attitude.

Plain-English answers drawn from the Specialty Coffee Association, World Coffee Research and the National Coffee Association. These explain general coffee knowledge, not the scores or identity of any untested coffee. The full searchable answer bank is available below when you need something more specific.

Are tasting notes ingredients added to coffee?

Usually not. Notes such as citrus, cocoa or jasmine describe aromas and flavors a taster perceives in brewed coffee; they are not an ingredient list. Flavored coffees are a separate category. A roaster's tasting notes are its descriptions, not proof that we independently tasted that bag.

Why this matters: A descriptive assessment records perceived sensory characteristics. It is separate from an evaluator's judgment of quality.

Explore the flavor wheelSource: Specialty Coffee Association — Coffee Value Assessment

What is the difference between washed, natural and honey coffee?

In broad terms, washed coffee is depulped and its mucilage is removed before drying; natural coffee dries inside the whole cherry; honey coffee is depulped but dried with some mucilage remaining. These process labels do not guarantee a particular flavor or a higher score.

Why this matters: Processing choices influence fermentation and drying, but variety, ripeness, handling and roasting also affect the cup.

Compare coffee processesSource: National Coffee Association — Coffee Processes

Is Arabica a coffee variety?

Arabica is a species, Coffea arabica. Bourbon, Typica, and many other named lines are varieties within that species. A variety name can help explain agronomic traits, but it cannot identify a farm or establish that a particular lot tastes a certain way.

Why this matters: Growing environment, plant health and postharvest decisions matter alongside genetics.

Understand coffee geneticsSource: World Coffee Research — Arabica catalog

Is dark roast stronger than light roast?

Dark roast can taste more bitter or intensely roasted, but that does not by itself mean it contains more caffeine. Roast color labels are not uniform across companies. Compare the same coffee brewed at the same dose before attributing flavor or strength to roast alone.

Why this matters: Roast degree affects flavor, while brewing dose and recipe affect the concentration in your cup.

Read the roasting guideSource: National Coffee Association — Coffee Roasts

How should I store whole-bean coffee?

Keep beans in an airtight, opaque container in a cool, dry, dark place, away from moisture and heat. Grind just before brewing when practical. Freshness depends on the roast, packaging and how the coffee has been stored; a single universal peak-freshness date is not reliable for every bag.

Why this matters: Air, light, warmth and moisture all speed flavor loss or create storage problems.

Explore brewing methodsSource: National Coffee Association — Storage and Shelf Life

Can one tasting score prove which coffee is best?

No. A score reflects a particular evaluation method, sample and taster or panel. The Specialty Coffee Association distinguishes sensory descriptions, judgments of quality, physical characteristics and information such as origin traceability. We publish our own scores only for coffees actually brewed and reviewed by us.

Why this matters: A competition result, a roaster's flavor description and an independent tasting score answer different questions; they should not be converted into one universal ranking.

How we research and rate coffeeSource: Specialty Coffee Association — Coffee Value Assessment

Research update · Genetics

Is Pink Bourbon actually a Bourbon?

Genetic tests reported by Cafe Imports in 2017 and 2023 indicate that sampled Pink Bourbon material belongs closer to Ethiopian landrace ancestry than the traditional Bourbon variety. The older Red × Yellow Bourbon origin story should not be repeated as established fact.

A farmer or roaster may use Pink Bourbon as the trade name for a pink-cherry coffee; a name and cherry color do not prove genetic parentage. Some tested samples had mixed markers, so the identity of any particular lot still needs evidence.

Read the corrected comparisonSource: Cafe Imports — Pink Bourbon genetics report (2023)

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COFFEE SCIENCEAnswer

Why does coffee taste bitter?

Coffee’s bitterness is not caused by a single substance, but by a complex interaction between caffeine, chlorogenic acid lactones, and phenylindanes created during roasting. While caffeine is a well-known bitter agent, it accounts for only a fraction of the total perception. Bitterness is primarily a byproduct of the Maillard reaction and thermal degradation during roasting, which transforms raw bean compounds into diverse bitter-tasting molecules that interact with multiple human bitter taste receptors.

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How does water temperature affect coffee extraction?

Water temperature primarily dictates the rate of extraction rather than the final flavor profile. While higher temperatures accelerate the dissolution of coffee solids, research indicates that if you achieve the same target strength (TDS) and extraction yield (PE) by adjusting grind size or brew time, the sensory difference between common brewing temperatures is negligible. Temperature is a tool for controlling extraction speed, not a direct flavor modifier in isolation.

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What is TDS in coffee brewing?

Total Dissolved Solids (TDS) measures the concentration of coffee solids dissolved in water, representing the physical strength of the brewed beverage. Expressed as a percentage, it quantifies how much of the final cup is coffee material versus water. While TDS indicates strength, it does not measure extraction efficiency or flavor quality on its own; it must be paired with Extraction Yield (PE) to understand if a coffee is balanced, under-extracted, or over-extracted.

COFFEE SCIENCEWater
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Why does coffee taste sour when under-extracted?

Under-extracted coffee tastes sour because acids and salts are the first compounds to dissolve during brewing. When the extraction yield is too low, these early-extracting compounds dominate the cup before the sugars and heavier flavor compounds have time to balance them out, resulting in a sharp, thin, and unpleasantly acidic flavor profile.

COFFEE SCIENCESpecialty coffeeAcidity
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What is the role of CO2 in coffee brewing?

Carbon dioxide (CO2) is a byproduct of roasting that acts as a physical barrier during brewing. Because CO2 is trapped inside coffee cells, it pushes water away from the grounds upon contact, potentially inhibiting even extraction. The bloom—a brief wetting stage—allows this gas to escape, ensuring water can fully penetrate the grounds to dissolve flavor compounds effectively.

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What causes coffee to taste bitter?

Bitterness in coffee is primarily caused by over-extraction, where too many soluble compounds—including those that are inherently bitter—are pulled from the grounds. This often happens when the grind is too fine, the water temperature is too high, or the contact time between water and coffee is too long, resulting in an unbalanced, harsh flavor profile.

COFFEE SCIENCESpecialty coffeeBitterness
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What is the Maillard reaction in coffee roasting?

The Maillard reaction is a chemical reaction between amino acids and reducing sugars that occurs during coffee roasting. It is responsible for the development of complex flavors, browning of the beans, and the creation of aromatic compounds. This reaction typically begins after the beans have dried and continues until the first crack, defining the roast profile and final cup quality.

COFFEE SCIENCESpecialty coffeeTypica
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What is total dissolved solids (TDS) in coffee?

Total Dissolved Solids (TDS) is a measurement of the concentration of coffee particles dissolved in water, typically expressed as a percentage. It indicates the strength of the brewed coffee. By using a refractometer to measure TDS, brewers can calculate extraction yield, ensuring their coffee is neither too weak nor too strong, and achieving a consistent, balanced flavor profile.

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What are the main acids in coffee?

The main acids in coffee include chlorogenic, citric, malic, and phosphoric acids. These compounds are responsible for the bright, vibrant, and complex acidity that characterizes high-quality specialty coffee. While chlorogenic acid is the most abundant, the balance of citric and malic acids often determines whether a coffee tastes citrusy, apple-like, or crisp.

COFFEE SCIENCESpecialty coffeeAcidity
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Why does coffee bloom?

Coffee blooms because hot water triggers the rapid release of carbon dioxide (CO2) trapped within the grounds. This gas, a byproduct of the roasting process, expands and escapes when it contacts water, causing the coffee bed to puff up. Blooming is a vital step in brewing that ensures the grounds are fully saturated for an even, consistent extraction.

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How does pressure affect espresso extraction?

Pressure is essential for espresso extraction, as it forces hot water through a tightly packed, fine bed of coffee at high force—typically 9 bars. This pressure emulsifies the coffee oils, creating the signature crema and concentrating the flavor. Variations in pressure directly impact the extraction rate, body, and balance of the final shot.

COFFEE SCIENCECremaSpecialty coffee
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How does water hardness affect coffee flavor?

Water hardness, caused by dissolved minerals like magnesium and calcium, significantly impacts coffee flavor. Magnesium helps extract fruity and floral notes, while calcium can contribute to a heavier body. However, excessive hardness can lead to flat, dull flavors or even scale buildup in equipment, while water that is too soft may result in a thin, overly acidic, or sour cup.

COFFEE SCIENCEWaterSpecialty coffee
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How does grind size affect extraction time?

Grind size is the most significant factor in controlling extraction time. A finer grind increases the surface area of the coffee, allowing water to extract flavor more quickly, which shortens the required brew time. A coarser grind decreases surface area, slowing the extraction process and requiring a longer contact time to achieve a balanced, flavorful cup.

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What is TDS in coffee?

TDS, or Total Dissolved Solids, is a measurement of the concentration of coffee particles dissolved in your brewed beverage. It represents the strength of the coffee, indicating how much coffee material has been extracted into the water. By measuring TDS with a refractometer, brewers can objectively determine if their coffee is under-extracted, over-extracted, or perfectly balanced.

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How does water temperature affect extraction?

Water temperature is a primary driver of extraction speed and efficiency. Higher temperatures increase the solubility of coffee compounds, allowing for faster extraction of acids, sugars, and bitter compounds. Lower temperatures slow this process, often resulting in a cleaner, more acidic cup, but requiring longer contact times to achieve a balanced extraction without leaving the coffee tasting thin or sour.

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What is the Maillard reaction in coffee?

The Maillard reaction is a complex chemical reaction between amino acids and reducing sugars that occurs during the roasting process. It is responsible for the development of browning, complex flavors, and aromatic compounds in coffee. This reaction begins as the beans heat up and is essential for transforming raw, grassy green coffee into the flavorful beans we brew.

COFFEE SCIENCETerroirRoasting
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How does water chemistry affect coffee taste?

Water chemistry is fundamental to coffee taste because coffee is over 98% water. Minerals like magnesium and calcium act as 'extractors' that pull flavor compounds from the beans, while alkalinity buffers the acidity. If your water is too soft, the coffee may taste flat or sour; if it is too hard, it can taste chalky or bitter.

COFFEE SCIENCEWaterAcidity
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Does grind size affect extraction time?

Yes, grind size is the primary factor in controlling extraction time. A finer grind increases the surface area of the coffee, which slows the flow of water and speeds up the extraction rate. Conversely, a coarser grind allows water to pass through more quickly, resulting in a slower extraction rate and a potentially weaker cup.

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What is coffee extraction yield?

Coffee extraction yield is the percentage of the dry coffee grounds that actually dissolves into your final cup of brewed coffee. It measures how much of the coffee's soluble material—such as sugars, acids, and oils—has been pulled out during the brewing process, with an ideal range typically falling between 18% and 22% for balanced flavor.

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Why does coffee taste bitter when over-extracted?

Coffee tastes bitter when over-extracted because the water has dissolved too many of the coffee's less desirable, heavy compounds. As extraction continues, the water pulls out tannins and other complex molecules that are inherently bitter. This happens when the grind is too fine, the water is too hot, or the contact time is too long, resulting in an unbalanced, harsh cup.

COFFEE SCIENCEBitternessAstringency
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Does roast degree affect caffeine concentration?

Roast degree has a negligible effect on the total caffeine content of a coffee bean. While roasting causes beans to lose mass and expand, the caffeine molecule itself is highly stable and does not break down significantly during the roasting process. Therefore, whether you choose a light or dark roast, the caffeine content remains largely consistent by weight.

COFFEE SCIENCESpecialty coffeeDark roast
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What causes coffee to bloom?

The coffee bloom is caused by the rapid release of carbon dioxide (CO2) trapped inside the beans during the roasting process. When hot water first hits the fresh grounds, the gas escapes, causing the coffee to bubble and expand. This process is a hallmark of freshness and is essential for ensuring even water contact and optimal extraction.

COFFEE SCIENCEWaterFreshness & storage
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What is TDS in coffee and why does it matter?

TDS, or Total Dissolved Solids, is a measurement of the concentration of coffee particles dissolved in your brewed cup. It is measured using a refractometer and is expressed as a percentage. TDS matters because it provides an objective way to quantify the strength of your coffee, allowing you to dial in your brewing recipe for consistent, repeatable results.

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Does adding salt to coffee really reduce bitterness?

Yes, adding a tiny pinch of salt to coffee can effectively reduce perceived bitterness. Sodium ions in salt interact with your tongue's taste receptors, suppressing the brain's perception of bitter compounds without necessarily making the coffee taste salty. This coffee hack is a well-documented phenomenon in sensory science, though it is best used sparingly to avoid masking the coffee's natural, nuanced flavor profile.

COFFEE SCIENCEBitternessAstringency
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What are diterpenes in coffee?

Diterpenes are naturally occurring, oil-soluble compounds found in coffee beans, primarily cafestol and kahweol. While they possess potential anti-carcinogenic and anti-inflammatory properties, they are best known for their ability to raise serum LDL cholesterol levels when consumed in unfiltered brews. Because these compounds are lipids, they are effectively trapped by paper filters; consequently, brewing methods like French press, Turkish, or boiled coffee retain high concentrations, whereas paper-filtered coffee contains negligible amounts.

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How does water temperature affect espresso extraction?

Water temperature directly dictates the kinetics of extraction, with higher temperatures accelerating the dissolution of coffee solids, including bitter and astringent compounds. While the Specialty Coffee Association suggests a range of 197°F to 205°F (92°C–96°C), temperature is a tool for managing extraction yield rather than a flavor panacea. Increasing heat predictably raises Total Dissolved Solids (TDS) and extraction yield, but excessive heat often results in acrid, over-extracted profiles that mask the nuanced work of the coffee producer.

COFFEE SCIENCEBitternessAstringency
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What is the difference between erosion and diffusion in coffee?

Diffusion is the internal movement of soluble compounds from the intact cellular structure of a coffee particle to its surface, while erosion is the mechanical breakdown of the particle surface by water flow. Diffusion is a slow, concentration-driven process occurring within the grain, whereas erosion is a physical, flow-induced process that releases surface fines and alters the bed's permeability during brewing.

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How does grind size affect extraction rate?

Grind size dictates extraction rate by altering the total surface area available for water contact and the distance solutes must travel to exit the coffee cell structure. Finer grinds increase surface area and shorten diffusion paths, accelerating extraction, while also reducing bed permeability, which slows water flow. Conversely, coarser grinds increase flow rates but require longer contact times to achieve the same extraction yield due to the increased distance solutes must travel from the center of larger particles.

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Why does under-extracted coffee taste sour?

Under-extracted coffee tastes sour because the acids in the coffee bean are the first compounds to be dissolved during the brewing process. If the water does not spend enough time in contact with the grounds, or if the grind is too coarse, the brewing process stops before the sweeter sugars and bitter compounds can balance out those initial sharp acids.

COFFEE SCIENCEBitternessSweetness
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What is the order of coffee extraction?

Coffee extraction follows a predictable sequence: acids and salts are extracted first, followed by sugars and caramels, and finally, bitter plant fibers. A balanced cup of coffee is achieved by stopping the extraction process at the point where the sweetness of the sugars perfectly offsets the initial acidity and the final bitterness.

COFFEE SCIENCEBitternessAstringency
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Does extraction yield affect caffeine content?

Yes, extraction yield directly affects caffeine content because caffeine is one of the first compounds to be extracted from coffee grounds. As you increase your extraction yield, you extract more of the available caffeine. However, because caffeine is highly soluble, it is almost entirely extracted early in the brewing process, meaning even moderate extraction levels will capture the majority of the caffeine.

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How does water chemistry affect coffee extraction?

Water chemistry influences coffee extraction through mineral content and alkalinity. Magnesium and calcium ions act as solvents that bind to flavor compounds, with magnesium often highlighting fruity notes and calcium enhancing body. Alkalinity, primarily from bicarbonate, buffers coffee acids; high levels can neutralize acidity, leading to flat or bitter flavors. The Specialty Coffee Association recommends a total dissolved solids (TDS) range of 75–250 ppm, with ideal alkalinity between 40–75 ppm CaCO3 to balance extraction and flavor clarity.

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Why does coffee bloom when you pour water on it?

Coffee blooms because hot water triggers the rapid release of carbon dioxide gas trapped inside the beans during the roasting process. This escaping gas causes the grounds to bubble and swell. By allowing this gas to escape during a 30–45 second bloom stage before the main pour, you ensure water can evenly saturate the grounds, which prevents uneven extraction and results in a more balanced, flavorful cup of coffee.

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What is the science behind coffee extraction?

Coffee extraction is the chemical process of dissolving soluble compounds—such as acids, sugars, and oils—from ground coffee into water. Approximately 28% of a coffee bean's mass is water-soluble, but the ideal extraction yield for a balanced cup is 18–22%. This process is governed by variables including water temperature, grind size, and contact time. Achieving the perfect balance requires managing these factors to extract desirable flavors while avoiding the bitterness that occurs when over-extracting heavier compounds.

COFFEE SCIENCESpecialty coffeeBitterness
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Does the Maillard reaction happen during roasting?

The Maillard reaction is a chemical process between amino acids and reducing sugars that occurs when food is heated, typically starting above 285°F (140°C). First described in 1912, this non-enzymatic browning reaction creates complex flavor compounds and a distinct brown color in foods like seared steak, toasted bread, and roasted vegetables. It is the fundamental process responsible for the savory aromas and rich tastes developed during high-temperature cooking.

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What causes floating oil on the surface of coffee?

Floating oil on the surface of coffee is caused by the release of natural coffee lipids during the brewing process. These oils are more prevalent in darker roasts, where the bean's cellular structure has been broken down by heat, and in brewing methods like French press or espresso that do not use paper filters to trap them.

COFFEE SCIENCECremaDark roast
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What acids are present in coffee?

Coffee contains a complex array of organic acids that define its flavor profile, including chlorogenic, citric, malic, acetic, and quinic acids. These acids are naturally occurring and contribute to the brightness, sweetness, and body of the coffee. Their concentration and balance are determined by the bean's origin, processing method, and the degree to which they are broken down during roasting.

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Is decaffeinated coffee more acidic than regular coffee?

Decaffeinated coffee is not more acidic than regular coffee; in fact, it is often marginally less acidic. While both types share similar pH levels—typically between 4.8 and 5.1—the decaffeination process can slightly reduce certain compounds. However, factors like bean origin, roast level, and brewing method have a much greater impact on coffee acidity and perceived brightness than the removal of caffeine.

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Does adding salt to coffee reduce bitterness?

Yes, adding a small amount of salt to coffee can effectively reduce bitterness. Salt works by activating sodium receptors on the tongue, which selectively suppresses the perception of bitter tastes while potentially enhancing other flavor notes. This is a well-documented phenomenon in taste perception, often used to balance out over-extracted or dark-roasted coffee that has become unpleasantly bitter.

COFFEE SCIENCEBitternessAstringency
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How much caffeine is extracted during brewing?

During standard brewing, approximately 75% to 90% of the caffeine present in the coffee grounds is extracted into the final beverage. Because caffeine is highly soluble in hot water, most of it is released early in the brewing process. The exact percentage depends on factors like grind size, water temperature, and total contact time.

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What happens to coffee beans during roasting?

During roasting, coffee beans undergo physical and chemical transformations at temperatures between 180°C and 240°C. Key processes include the Maillard reaction, caramelization, and pyrolysis, which break down sugars and chlorogenic acids to develop flavor, aroma, and color. Physically, beans lose moisture, decrease in density, and expand. The process typically lasts 5 to 15 minutes, during which beans transition from green to dark brown, eventually releasing gases during events known as the first and second cracks.

COFFEE SCIENCETypicaRoasting
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What is the significance of the 20-point extraction yield target?

The 20% extraction yield target is a benchmark in coffee science representing the percentage of the dry coffee mass that has been dissolved into the final brew. Aiming for an extraction yield between 18% and 22% is widely considered the 'sweet spot' for balanced flavor, where the coffee is neither sour from under-extraction nor bitter from over-extraction.

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How do I calculate extraction yield for a V60?

To calculate extraction yield for a V60, use the formula: (Beverage Weight × TDS%) ÷ Dry Coffee Dose. You will need a digital scale to measure your dry coffee dose and final beverage weight, and a coffee refractometer to determine the Total Dissolved Solids (TDS). This calculation reveals what percentage of your dry grounds successfully dissolved into your final brew.

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How does light roast differ from dark roast chemically?

Light and dark roasts differ primarily through the Maillard reaction and caramelization, which transform sugars and amino acids into complex flavor compounds. Light roasts preserve more original origin characteristics and volatile aromatic compounds, while dark roasts undergo further carbonization, creating smoky, bitter notes. Contrary to popular belief, light roasts often contain slightly more caffeine by weight due to less sublimation during roasting.

COFFEE SCIENCETerroirBitterness
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How does the Maillard reaction affect coffee flavor?

The Maillard reaction is a chemical process between amino acids and reducing sugars that occurs during roasting, significantly developing coffee flavor and color. It is responsible for creating complex, savory, and sweet notes, such as toasted bread, chocolate, and caramel. Controlling this reaction is essential for defining the final roast profile and the balance of the cup.

COFFEE SCIENCESweetnessChocolate
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Why does coffee bloom when hot water hits it?

Coffee blooms when hot water hits it because of the rapid release of carbon dioxide gas trapped inside the beans during the roasting process. This degassing phenomenon is a sign of freshness; as the gas escapes, it creates bubbles and expands the grounds, allowing water to better penetrate the coffee and ensure a more even extraction.

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What is the role of chlorogenic acids in coffee bitterness?

Chlorogenic acids are a group of antioxidants naturally present in green coffee that significantly influence its bitterness and acidity. During roasting, these acids break down into quinic and caffeic acids, which contribute to the coffee's perceived bitterness and astringency. The degree of this breakdown is a key factor in the flavor profile of different roast levels.

COFFEE SCIENCEBitternessAstringency
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Does grinding coffee beans generate enough heat to affect flavor?

Yes, grinding coffee beans can generate enough heat to affect flavor, especially in high-volume settings or with poorly designed grinders. Excessive heat can cause the volatile aromatic compounds in the coffee to evaporate prematurely, leading to a loss of freshness and a duller, less vibrant flavor profile in the final cup.

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What is the difference between solubility and extraction yield?

Solubility refers to the inherent ability of coffee compounds to dissolve in water, while extraction yield is the percentage of the dry coffee mass that has actually dissolved into the final brew. Solubility is a chemical property of the bean, whereas extraction yield is a measurable outcome of your specific brewing process and variables.

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What is the impact of light on coffee beans?

Light exposure, particularly UV rays, accelerates the degradation of roasted coffee beans through a process called photodegradation. This chemical breakdown destroys essential aromatic compounds and oils, leading to a stale, flat, and bland flavor profile. To preserve freshness, coffee should always be stored in opaque, airtight containers kept in a cool, dark location away from direct light.

COFFEE SCIENCESpecialty coffeeFreshness & storage
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How does agitation affect coffee extraction?

Agitation, or turbulence, is the physical disturbance of coffee grounds during brewing, such as stirring or swirling. It accelerates extraction by ensuring water consistently contacts fresh surfaces of the coffee particles. While controlled agitation helps achieve a balanced, full extraction, excessive turbulence can lead to over-extraction, resulting in bitter or astringent flavors in your final cup.

COFFEE SCIENCEBitternessAstringency
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What is the science of coffee filtration?

Coffee filtration is the physical separation of liquid coffee from insoluble grounds and oils using a porous medium. Paper filters use tightly bound fibers to trap fine sediment and lipids, resulting in a clean, bright cup with high flavor clarity. Conversely, metal filters allow oils and micro-grounds to pass through, creating a heavier, fuller-bodied brew with a more textured mouthfeel.

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Why does coffee taste different at high altitudes?

Coffee tastes different at high altitudes primarily because lower air pressure lowers the boiling point of water, which can lead to under-extraction. Additionally, high-altitude beans are denser due to slower maturation, requiring adjustments to brewing at altitude. To compensate for the lower water temperature, you may need to increase contact time or use a finer grind to ensure proper extraction.

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How do coffee oils affect flavor?

Coffee oils, or lipids, are essential for defining a coffee's mouthfeel, body, and aromatic intensity. While they do not provide sweetness or acidity directly, they act as carriers for volatile aromatic compounds and create a sense of viscosity on the palate. Brewing methods that retain these oils, such as metal filtration, result in a richer, heavier texture compared to paper-filtered coffee.

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What is the science of coffee solubility?

Coffee solubility is the process of selectively dissolving flavor compounds from coffee grounds into water. Compounds dissolve in a predictable sequence: organic acids and mineral salts extract first, followed by caffeine and sugars, and finally, heavier plant fibers and bitter compounds. Mastering extraction involves balancing these variables to achieve a desired flavor profile while avoiding over-extraction.

COFFEE SCIENCESpecialty coffeeBitterness
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How does the coffee cherry ripeness affect sugar content?

Coffee cherry ripeness is directly linked to sugar content, which is measured using the Brix scale. As a cherry matures, it accumulates higher concentrations of sugars and dry matter in the mucilage. Harvesting at peak ripeness ensures the highest potential for sweetness and complexity, whereas under-ripe cherries lack the necessary sugars to develop a balanced, high-quality cup.

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What is the effect of roasting on caffeine levels?

Roasting has a negligible effect on the total caffeine content of coffee beans. While roasting causes beans to lose mass and volume, caffeine is a chemically stable molecule that does not break down at typical roasting temperatures. Consequently, the caffeine concentration by weight may slightly increase in darker roasts, but the caffeine content per serving remains largely consistent across roast levels.

COFFEE SCIENCELight roastMedium roast
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Why does coffee taste different when cold?

Coffee tastes different when cold primarily because temperature alters our sensory perception of flavor and the chemical solubility of compounds. Cold temperatures suppress the perception of sweetness and acidity, while highlighting bitterness and body. Additionally, cold brew methods extract fewer acidic compounds than hot brewing, resulting in a smoother, less acidic profile that changes as the beverage warms.

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How does water hardness impact coffee taste?

Water hardness, defined by mineral content like calcium and magnesium, significantly influences coffee flavor and extraction efficiency. While moderate mineral levels can enhance sweetness and body, excessively hard water often leads to bitterness and scale buildup. Conversely, very soft water may result in a flat, overly acidic cup, as it lacks the necessary ions to properly extract complex coffee flavor compounds.

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What is the difference between TDS and extraction yield?

TDS (Total Dissolved Solids) measures the concentration or strength of your brewed coffee, while extraction yield measures the percentage of the dry coffee grounds that have been dissolved into the water. TDS is a snapshot of the liquid's intensity, whereas extraction yield tells you how much of the coffee's potential flavor you successfully pulled out.

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Does freezing coffee beans keep them fresh?

Yes, freezing coffee beans is an effective way to preserve freshness, provided they are stored in an airtight, moisture-proof container. Freezing significantly slows down the chemical reactions that cause staling, such as oxidation and the loss of volatile aromatics. To avoid condensation, only remove the amount of beans you need and return the rest to the freezer immediately.

COFFEE SCIENCESpecialty coffeeFreshness & storage
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What is the ideal water temperature for pour over?

The ideal water temperature for pour-over coffee is generally between 195°F and 205°F (90°C–96°C). This range is hot enough to efficiently extract flavor compounds from the grounds without scorching them. Lighter roasts often benefit from the higher end of this range, while darker roasts may taste better at slightly lower temperatures to avoid excessive bitterness.

COFFEE SCIENCESpecialty coffeeLight roast
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How does grind size affect extraction?

Grind size determines the total surface area of the coffee particles exposed to water. A finer grind increases surface area, leading to a faster extraction rate, while a coarser grind decreases surface area, slowing the extraction. Finding the right balance is essential to avoid under-extraction, which tastes sour, or over-extraction, which tastes bitter.

COFFEE SCIENCESpecialty coffeeBitterness
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What is the science behind the coffee bloom?

The coffee bloom is the rapid release of carbon dioxide gas trapped inside coffee beans during the roasting process. When hot water first hits fresh grounds, the gas escapes, causing the coffee to bubble and expand. This degassing process is essential because the gas can create a barrier that prevents water from fully extracting flavor from the grounds.

COFFEE SCIENCESpecialty coffeeWater
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Does coffee acidity come from the beans or the roast?

Coffee acidity is a result of both the beans' origin and the roast profile. The bean's terroir and variety determine the potential acids present, such as citric or malic acid, while the roast level dictates how those acids are developed or degraded. A lighter roast preserves the bean's inherent acidity, while a darker roast breaks those acids down.

COFFEE SCIENCESpecialty coffeeTerroir
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Why does coffee lose flavor after grinding?

Coffee loses flavor after grinding primarily due to oxidation and the rapid loss of volatile aromatic compounds. Grinding increases the surface area of the coffee by thousands of times, exposing the internal oils and aromatics to oxygen. This causes the coffee to stale quickly, resulting in a loss of the complex, vibrant flavors that define fresh coffee.

COFFEE SCIENCESpecialty coffeeGrinding
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What is the role of lipids in coffee crema?

Lipids, or coffee oils, are essential to the formation and stability of espresso crema. During the high-pressure extraction of espresso, these oils emulsify with carbon dioxide and water to create the thick, golden-brown foam known as crema. These lipids also contribute significantly to the mouthfeel and the lingering aftertaste of the espresso.

COFFEE SCIENCECremaSpecialty coffee
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What is the difference between Arabica and Robusta chemistry?

The primary chemical difference between Arabica and Robusta is their caffeine and lipid content. Robusta contains nearly twice as much caffeine as Arabica, which acts as a natural pesticide for the plant. Arabica, however, has higher concentrations of lipids and sugars, which contribute to its more complex, nuanced, and acidic flavor profile compared to the bolder, more bitter Robusta.

COFFEE SCIENCESpecialty coffeeArabica
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What is the chemical cause of coffee staling?

Coffee staling is primarily caused by oxidation, where oxygen reacts with volatile aromatic compounds, lipids, and phenolic acids, breaking them down into dull, papery, or rancid-tasting molecules. This chemical degradation is accelerated by moisture, heat, and light, which strip the coffee of its vibrant, fresh characteristics and lead to a loss of intensity and the development of unpleasant, woody off-flavors.

COFFEE SCIENCEOrganic
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