What Is Strong Coffee? Flavor, Caffeine, Concentration, and Why Strong Means Different Things
Author: Ukrainian Psychological Hub · Published: September 28, 2026 · Editorial Policy
Strong coffee is not one single thing. In coffee brewing science, strength most precisely means beverage concentration: how much dissolved coffee material is present in the drink, commonly measured as total dissolved solids, or TDS. In everyday language, however, strong can also mean bitter, dark-roasted, full-bodied, intensely aromatic, high in caffeine, highly concentrated per ounce, or simply capable of producing a noticeable stimulant effect. Those meanings can overlap, but they are not interchangeable.
That distinction matters because two coffees can reverse order depending on what you measure. An espresso can be far more concentrated than filter coffee while a large filter serving contains more total caffeine. A dark roast can taste more intense because burnt, bitter, smoky, and roasted notes are prominent while its caffeine dose is not predictably higher. A cup can also be high in caffeine without tasting especially bitter. Research on brewed coffee explicitly separates brew strength from extraction yield, and sensory work shows that changing concentration changes several flavor attributes rather than one simple “strength” sensation. Frost, Ristenpart, and Guinard describe brew strength as TDS and extraction yield as a separate variable in drip coffee.
If you remember only one rule, use this one: when someone calls coffee “strong,” ask strong in what sense—taste intensity, beverage concentration, caffeine per milliliter, total caffeine per serving, or subjective stimulant effect?
Strong coffee in one minute: five meanings people often combine
1. Brew strength: concentration of dissolved coffee solids
This is the technical brewing meaning. A higher-TDS beverage contains a greater proportion of dissolved coffee material relative to water. Within the same general brewing style, higher TDS is ordinarily experienced as a more concentrated cup, although the exact sensory profile also depends on roast, extraction, water, temperature, and the coffee itself. Controlled sensory research on drip coffee found systematic changes in bitterness, sourness, sweetness, thickness, persistence, and other attributes as TDS and extraction changed.
2. Flavor intensity: how forcefully the coffee tastes and smells
A consumer may mean that the coffee tastes bitter, roasted, smoky, dark, heavy, lingering, or aromatic. This is a sensory judgment, not a laboratory measurement of caffeine. Dark roasting can intensify burnt and bitter sensations, and brewing concentration can increase perceived flavor intensity, but neither property is identical to caffeine dose. A 2025 sensory study found bitter and burnt sensations more dominant in the dark-roasted coffee it tested.
3. Caffeine concentration: milligrams of caffeine per milliliter
A small beverage can contain a high concentration of caffeine even when its total serving is modest. Espresso is the obvious example: it is concentrated, so caffeine per unit volume can be high. But caffeine concentration is not the same measure as TDS because TDS includes many dissolved coffee compounds, not caffeine alone.
4. Total caffeine per serving: milligrams in the whole cup
This is the number that matters when the question is how much caffeine you actually consume. Serving size changes the answer dramatically. EFSA gives approximate reference values of 80 mg of caffeine for a 60 mL espresso and 90 mg for a 200 mL filter coffee, while emphasizing that caffeine content and portion sizes vary. EFSA’s caffeine guidance explicitly notes that coffee caffeine varies with bean type, manufacturing, and preparation.
5. Perceived strength: how powerful the coffee seems
Perceived strength combines chemistry with perception. Color, aroma, bitterness, body, packaging, labels, learned associations, previous coffee experience, expectations, and the drinker’s own sensory sensitivity can all contribute. A recent qualitative study of Brazilian coffee consumers found that “strong coffee” was commonly represented through darkness, bitterness, body, roasted or smoky aroma, astringency, intensity, and a functional “pick-me-up” meaning. Neves and colleagues concluded that strong coffee functions as a context-dependent cultural category rather than a single fixed sensory attribute.
What coffee professionals mean by brew strength
For brewed coffee, technical strength usually refers to the concentration of dissolved material in the beverage. Refractometers are commonly used to estimate total dissolved solids. If a filtered coffee reads a higher TDS than another comparable brew, it is more concentrated in this technical sense. The number says how concentrated the beverage is; it does not, by itself, tell you whether the coffee is delicious, bitter, under-extracted, over-extracted, high in caffeine, dark-roasted, or preferred by a particular person.
This matters because the historic coffee brewing control framework placed brew strength and extraction yield on separate axes. Modern research has retained the distinction while showing that sensory quality and consumer liking are more complicated than a single “ideal” box. Guinard and colleagues’ updated Coffee Brewing Control Chart work maps sensory properties and consumer liking across strength, extraction yield, and brew ratio.
Consumer preference is also not uniform. In one controlled study of 118 black-coffee consumers, preferences were spread across a wide range of brew strengths and extraction yields, with different preference clusters responding differently to TDS. Cotter and colleagues found that flavor intensity and acidity were important drivers of liking and that one universal ideal did not describe all consumers.
Strength and extraction are different variables
This is the most useful brewing distinction in the entire strong-coffee question. Strength asks: how concentrated is the liquid in the cup? Extraction asks: how much soluble material was removed from the dry coffee grounds during brewing? A beverage can be relatively concentrated at a modest extraction, or relatively dilute even when a substantial fraction of the soluble material has been extracted, depending on the recipe and beverage yield.
Imagine using a large dose of coffee with relatively little water. The resulting beverage can be concentrated because a lot of dissolved material is present per unit of liquid. Now imagine using the same coffee with much more water. You may extract a similar or even greater fraction of available soluble material, yet the resulting drink is more diluted. That is why “use more coffee” and “extract more from the coffee” are not the same instruction.
The distinction also explains a common brewing mistake: trying to make coffee stronger only by grinding much finer or extending contact time. Those changes primarily alter extraction kinetics. They may raise dissolved-solids concentration somewhat, but they also change which compounds enter the cup and can push sensory balance toward harsh bitterness, astringency, dryness, or muddiness. If the specific goal is a more concentrated cup, changing the coffee-to-water relationship is the more direct lever; grind, temperature, agitation, and time should then be adjusted to keep extraction palatable.
Coffee-to-water ratio: the most direct recipe lever for stronger brewed coffee
Coffee-to-water ratio describes the mass of dry coffee relative to brew water. If you keep water constant and increase the dry coffee dose, you usually produce a more concentrated beverage, provided the brewer can wet and extract the larger bed effectively. If you keep coffee constant and reduce water, the beverage also tends to become more concentrated. Ratio is therefore an input; measured TDS is an output.
There is no scientifically universal ratio at which ordinary coffee suddenly becomes “strong.” Brew method, grinder, roast, water chemistry, basket geometry, filter, desired beverage size, and personal preference all matter. Studies that manipulate coffee-to-water ratio find meaningful sensory changes, but the direction and magnitude of specific attributes depend on the broader brewing system. Seninde and colleagues experimentally varied roast degree, coffee-to-water ratio, brewing method, and species in cold brew and found that all contributed to sensory outcomes.
A practical way to increase strength without changing everything at once is to keep water, grind, temperature, and technique stable and raise the coffee dose in small steps. For example, if your current filter recipe uses 30 g of coffee with 500 g of water, try 33 g with the same water before making a larger change. That moves the input ratio from about 1:16.7 to about 1:15.2. Taste the result. If it becomes concentrated but hollow or harsh, the next adjustment may be grind or contact time rather than another dose increase. The numbers here are an example of controlled experimentation, not a universal standard.
For repeatability, weigh both coffee and water rather than relying on scoops and cup marks. Write down dose, water mass, grind setting, brew time, and final beverage mass if you want to troubleshoot systematically. “Strong” becomes much easier to control when the recipe produces a traceable result instead of a vague impression.
Does strong coffee have more caffeine?
Not necessarily. Stronger taste, higher TDS, darker roast, and higher caffeine are different properties. A coffee can taste extremely bitter and roasted while containing less total caffeine than a milder-tasting larger drink. Conversely, a smooth coffee can deliver a substantial caffeine dose.
Caffeine in the cup depends on several variables: the amount of dry coffee used, species and composition of the beans, caffeine concentration in the roasted material, grind and extraction conditions, brewing method, beverage yield, and serving size. Reviews and direct measurements consistently show considerable variation across coffee preparations. A study of commercial espressos, for example, found a sixfold range in caffeine levels across 20 samples, illustrating why “one espresso” or “one strong coffee” is not a precise caffeine unit. Crozier and colleagues attributed much of the observed commercial espresso variation to bean composition and preparation, especially the amount of coffee used.
If you want to compare stimulant dose, use milligrams of caffeine per serving whenever reliable data are available. If you want to compare how concentrated the caffeine is, use milligrams per unit volume. If you want to compare brew concentration, use TDS. These three measurements answer three different questions.
Caffeine concentration versus total caffeine: why serving size changes the answer
A concentrated beverage can have more caffeine per milliliter but less caffeine in the whole serving. This is the simplest way to understand espresso versus filter coffee. EFSA’s approximate examples—80 mg in 60 mL of espresso and 90 mg in 200 mL of filter coffee—show the logic clearly: the espresso example is much more concentrated in caffeine per milliliter, yet the larger filter serving contains slightly more caffeine in total. EFSA stresses that these figures are approximate because real coffee and portion sizes vary.
Real-world variation can be much larger than those reference examples. Commercial espresso measurements have found very large differences from shop to shop. That means visual size alone cannot tell you the exact caffeine dose, and a menu word such as “bold,” “intense,” or “strong” is not a substitute for measured caffeine information.
The same principle applies to cold-brew concentrates and other beverages intended for dilution. A concentrate can have high caffeine and coffee-solids concentration per milliliter, but the final serving depends on how much concentrate is used and how much water, milk, or ice is added.
Is espresso stronger than regular coffee?
Espresso is generally stronger in the sense of beverage concentration: it contains a high concentration of dissolved and suspended coffee material in a small amount of liquid. It also commonly contains more caffeine per milliliter than filter coffee. But whether it contains more total caffeine per serving depends on the dose, shot recipe, number of shots, and the size and recipe of the comparison drink.
So the answer depends on the unit. Stronger flavor per sip? Often yes. Higher coffee-solids concentration? Yes, as a general characteristic of espresso. Higher caffeine concentration per milliliter? Usually. More total caffeine than a large filter coffee? Not automatically. A double or triple espresso changes the comparison again.
Espresso also has a different texture and aroma-release profile because of its high concentration, emulsified oils, fine particles, crema, serving temperature, and small volume. Those features intensify the sensory experience, which can make “stronger” feel self-evident even before caffeine is considered.
Does dark roast mean strong coffee?
Dark roast can mean strong flavor to a drinker, but roast level is not brew strength. Roast describes how the beans were thermally developed; strength describes the resulting beverage concentration when used technically. You can brew a dilute dark roast and a highly concentrated light roast.
Darker roasting often produces sensory cues that people associate with strength: darker color, more pronounced roast character, smoke or burnt notes, bitterness, and a heavier or more persistent impression. Controlled sensory work has found bitter and burnt sensations to dominate dark-roasted samples more than medium-roasted samples under the studied conditions. Cleve and colleagues documented roast-dependent differences in flavor perception and aroma release in medium and dark roasted Arabica coffees.
Caffeine is where the popular shortcut fails. The research literature does not support a simple rule that darker always means more caffeinated or that lighter always means more caffeinated under every way of dosing and brewing. A 2024 controlled filter-coffee study found that, under identical brew conditions, darker roasts generally produced lower caffeine concentrations than light and medium roasts, but at identical extraction yields the relationship could reverse. The authors emphasized competing effects of roast-related porosity, extraction, and thermal loss. Lindsey and colleagues show why roast color alone is an unreliable caffeine predictor.
The practical conclusion is straightforward: choose roast level primarily for the flavor profile you want. For caffeine, look at coffee dose, bean composition, method, serving size, and measured caffeine data where available. For brew strength, look at the recipe and concentration.
Why bitter coffee is often called strong—and why bitterness is not caffeine
Bitterness is one of the strongest learned cues for “strong coffee,” but coffee bitterness is chemically complex. Caffeine is bitter, yet it is only one contributor. Coffee contains multiple bitter-active compounds, and roasting creates or transforms compounds that can alter bitterness.
Molecular sensory research has identified several coffee constituents that activate human bitter taste receptors, some at greater receptor potency than caffeine in experimental systems. Lang and colleagues concluded that coffee bitterness is orchestrated by interactions among multiple compounds and bitter receptors.
A separate flavoromics study isolated five compounds that, when recombined as a mixture, significantly enhanced coffee bitterness; roasting experiments showed that these compounds were generated during roasting. Gao, Tello, and Peterson provide direct evidence that roast-derived compounds can enhance bitterness independently of a simple caffeine explanation.
This is why tasting bitterness cannot tell you a cup’s caffeine dose. Dark roasting, extraction conditions, water chemistry, species, processing, temperature, and individual taste sensitivity can all affect perceived bitterness. The same caffeine amount can also be experienced differently when the rest of the beverage matrix changes.
Body, aroma, color, and aftertaste can all make coffee feel stronger
People do not perceive coffee through taste alone. Flavor is a multisensory construction that combines taste, retronasal aroma, orthonasal aroma, temperature, mouthfeel, visual appearance, and learned expectations. A coffee that is darker in color, thicker in body, more aromatic, and longer in aftertaste can feel “stronger” even if another coffee has more caffeine.
Recent work on the everyday meaning of strong coffee makes this especially clear. In the Brazilian qualitative study by Neves and colleagues, darkness, bitterness, body, smoky or burnt character, astringency, and flavor/aroma intensity all appeared in how participants described strong coffee, while stimulant function was another but separate dimension. The study used 35 in-depth interviews plus guided tastings and therefore offers rich consumer-language evidence, although its cultural setting should not be treated as universal.
Individual sensory biology also matters. A 2026 study of coffee aroma found substantial interindividual differences in detection and intensity of odor-active molecules, related in that study to olfactory thresholds and a genetic polymorphism involving OBPIIa. Diana and colleagues provide one example of why the same coffee aroma need not have the same perceived intensity for every person.
Expectation changes perceived strength without changing the coffee’s chemistry
The physical beverage matters, and so does what the drinker expects. Expectation can influence attention, interpretation, and ratings of sensory experience. This does not mean labels magically change dissolved solids or caffeine. It means perception is produced by sensory input interpreted through prior information and learned associations.
In a field experiment with 123 participants, a package claim saying “extra strong” increased perceived coffee strength, while a visual metaphor of strength also influenced expectations and evaluations. Fenko, de Vries, and van Rompay experimentally demonstrated that packaging cues can change strength perception even when the tasted coffee itself is held constant across conditions.
Color carries expectations too. In a 2025 study of 238 specialty-coffee consumers, brown packaging was associated with bitterness, dark roast, intense aroma, and cocoa notes. Carvalho and colleagues show how visual cues can create sensory expectations before the drink reaches the mouth.
Labels can affect experience during tasting as well as expectations before it. A 2026 within-subject experiment presented the same specialty coffee with different processing labels and found changes in expected and experienced sensory judgments and liking. Carvalho, de Sousa, and Nadaleti illustrate how descriptive information can become part of the perceptual context of a coffee.
For strong coffee, this means words such as bold, intense, extra strong, dark, Italian, robust, or double may guide attention toward cues that fit the label. The measured coffee is still the measured coffee. The experience, however, includes expectation.
How to make coffee stronger without simply making it harsher
If you want a more concentrated cup
Change the coffee-to-water relationship first. Increase the dry coffee dose while holding water constant, or reduce water while holding coffee constant. Make a modest change, taste, and then adjust grind or contact time only if extraction becomes unbalanced. This approach targets concentration directly instead of trying to obtain strength by indiscriminately extracting longer.
If you want stronger flavor
Define the flavor you actually want. More roastiness and bitterness may point toward a darker roast. More body may point toward a method with less paper filtration or a higher concentration. More aromatic intensity may come from fresher coffee, a different origin or process, a different grind just before brewing, or a more concentrated recipe. “Stronger flavor” is too broad to be solved by one variable.
If you want more caffeine
Treat caffeine as a dose question. Using more caffeinated coffee material and consuming a larger extracted dose generally raises the potential caffeine intake, but the exact result depends on species, coffee dose, extraction, and serving. Do not use bitterness or darkness as a caffeine meter. When a product provides reliable caffeine information, compare milligrams per serving.
If you want strong coffee with less bitterness
Increase concentration gradually rather than forcing extraction. Keep a reproducible recipe, avoid an excessively fine grind for the method, and avoid extending contact time merely to chase intensity. You can also choose a coffee and roast whose flavor profile is less dominated by roast bitterness. Strong and bitter do not have to travel together because concentration, extraction, roast chemistry, and bitterness are different dimensions.
If your coffee tastes weak even though you use plenty of grounds
Check extraction and brew mechanics rather than adding coffee indefinitely. Water may be channeling through a filter bed, grind may be too coarse for the contact time, water may pass too quickly, immersion may be too short, grounds may not be fully wetted, or your final beverage may be more diluted than you think. A large dose that is poorly extracted can produce an expensive but disappointing cup.
If your coffee tastes strong but unpleasant
Separate concentration from defect. Is it too bitter, too sour, too dry, smoky, burnt, muddy, or simply too concentrated? Each points to a different adjustment. A cup that is too concentrated can be diluted. Excessive bitterness or dryness may require a coarser grind, shorter effective contact, less agitation, lower extraction, a different roast, or a different coffee. Sourness in a concentrated cup can reflect extraction imbalance rather than insufficient strength.
Strong coffee and the stimulant effect: what you feel is not a direct caffeine assay
Caffeine is a central nervous system stimulant, and moderate doses can increase alertness and reduce sleepiness. But subjective response varies. Habitual use, tolerance, timing, sleep debt, body size, metabolism, medications, pregnancy, anxiety sensitivity, expectations, and the rest of a person’s caffeine intake can all change how a serving feels. EFSA notes both stimulant effects and substantial variability in caffeine exposure and provides safety conclusions for the general healthy population.
This is another reason “it felt strong” cannot identify the beverage’s TDS or caffeine content. A person who is caffeine-naive may notice a modest dose strongly; a habitual user may report less subjective effect from a larger dose. Expectations can also shape the interpretation of arousal. The drink and the drinker both matter.
For most adults, the U.S. FDA cites 400 mg of caffeine per day as an amount not generally associated with negative effects, while emphasizing wide differences in sensitivity and noting that some medical conditions, medications, pregnancy, and other circumstances can change appropriate limits. FDA guidance also lists anxiety, jitters, palpitations, insomnia, digestive symptoms, nausea, and headache among possible signs of excessive caffeine intake.
EFSA concludes that single doses up to 200 mg do not raise safety concerns for the general healthy adult population, while a single 100 mg dose may affect sleep in some adults when consumed close to bedtime; it also gives different guidance for pregnancy and younger populations. These figures are population-level safety conclusions, not individualized medical advice.
Why “strongest coffee” lists are usually comparing different things
Online lists of the “strongest coffees” often mix at least four categories: products marketed with aggressive strength language, beans or blends with high caffeine potential, highly concentrated recipes, and large servings containing a high total caffeine dose. Without a measurement unit, the ranking is undefined.
A meaningful comparison must specify the metric. For caffeine, report milligrams per serving and ideally serving size. For caffeine concentration, report milligrams per milliliter or ounce. For brew strength, report TDS. For a recipe, report coffee and water by mass. For sensory intensity, describe the attribute—bitterness, roastiness, body, aroma, persistence—or use a validated sensory scale. “Strongest” becomes informative only when the underlying variable is named.
Common strong-coffee myths
Myth: dark roast always has more caffeine
Roast darkness is not a reliable caffeine shortcut. Controlled studies show that the result depends on dosing, extraction yield, roast development, and how the comparison is normalized. The 2024 filter-coffee study by Lindsey and colleagues demonstrates why apparently contradictory roast-caffeine claims can both emerge under different comparison conditions.
Myth: bitter means caffeinated
Caffeine contributes bitterness, but coffee bitterness is produced by a network of compounds and roast-derived chemistry. Human bitter-receptor research and flavoromics both show substantial non-caffeine contributions to coffee bitterness. Roasting can also generate mixtures of compounds that enhance bitterness.
Myth: espresso always has more caffeine than drip coffee
Espresso is more concentrated, but total caffeine depends on serving and recipe. A small espresso can contain less total caffeine than a large filter coffee, even while containing more caffeine per milliliter. EFSA’s approximate serving examples make this distinction explicit.
Myth: brewing longer is the best way to make coffee stronger
Longer contact changes extraction, and its effect depends on method. It is not a clean substitute for changing concentration. If the goal is stronger brew concentration, ratio is the more direct variable. Extending extraction indiscriminately can change bitterness, acidity, astringency, and balance.
Myth: a coffee bag’s strength number is a universal scientific scale
Retail strength scales are not one globally standardized measurement. Depending on the brand, a strength number may encode roast level, intended flavor intensity, blend design, or an internal product ladder. It should not be assumed to equal TDS or caffeine content unless the producer explicitly defines and measures it that way.
A practical decision guide: choose the meaning of strong you actually want
If you want more coffee flavor per sip, increase beverage concentration gradually and keep extraction balanced. If you want a darker, roast-driven sensory profile, choose a darker roast and adjust brewing for that coffee. If you want more caffeine, compare caffeine dose rather than roast color or bitterness. If you want espresso-like intensity, choose a concentrated brewing method or smaller beverage ratio. If you want a heavier mouthfeel, consider filtration and suspended material as well as concentration. If you want consistency, measure your inputs and repeat the recipe.
If two people disagree about whether a coffee is strong, they may both be accurately reporting different variables. One may mean “very bitter and dark,” another “high TDS,” another “lots of caffeine,” and another “this woke me up.” Naming the variable resolves most of the argument.
FAQ
What is the definition of strong coffee?
Technically, brew strength refers to beverage concentration, commonly measured as total dissolved solids. In everyday speech, strong coffee can also mean intense flavor, dark roast character, bitterness, high caffeine, heavy body, or a strong subjective stimulant effect. The technically safest definition is therefore: strong in which dimension?
Does stronger coffee mean more caffeine?
No. Higher brew concentration can sometimes accompany a larger coffee dose and therefore more caffeine, but flavor strength and caffeine are not equivalent. Caffeine depends on bean composition, dose, extraction, brewing method, beverage volume, and serving size.
Is espresso the strongest coffee?
Espresso is among the most concentrated common coffee beverages and often has high caffeine concentration per milliliter. It does not automatically contain the most total caffeine per serving because espresso servings are small and filter or other drinks may be much larger.
Is dark roast stronger than light roast?
Dark roast often tastes stronger in the sense of roastiness, bitterness, smoke, and burnt notes. It is not automatically more concentrated and is not reliably more caffeinated. Brew recipe determines concentration; roast and extraction conditions interact with caffeine in more complicated ways.
How can I make coffee stronger without making it bitter?
Increase coffee relative to water in modest steps while keeping the rest of the recipe stable. Then adjust grind or contact time only as needed to preserve balanced extraction. This targets concentration directly instead of using excessive extraction to create intensity.
What does TDS mean in coffee?
TDS means total dissolved solids. In brewed coffee it is used as a measure of the concentration of dissolved coffee material in the beverage. It is a measure of brew strength, not a direct caffeine measurement and not the same as extraction yield.
What is extraction yield?
Extraction yield estimates how much of the dry coffee mass was dissolved and transferred into the beverage. Strength describes the concentration of the liquid; extraction yield describes how much material was removed from the grounds. The two are related by the recipe but are conceptually different.
Why can a smooth coffee be high in caffeine?
Because caffeine dose is not identical to bitterness or roast intensity. A smooth beverage can be made from a large coffee dose, a caffeine-rich blend, or a large serving. Conversely, a dark bitter cup can have a lower total caffeine dose.
Why does coffee taste stronger when it looks darker?
Dark color can signal roast intensity and can also create learned expectations of bitterness and strength. Sensory input and expectation work together. Research on strong-coffee meaning and packaging cues shows that darkness, visual metaphors, and labels can affect anticipated or perceived strength, even though those cues do not themselves measure caffeine or TDS.
The clearest way to talk about strong coffee
The word strong is useful only after the variable is named. In brewing science, strong usually means a more concentrated beverage. In sensory language, it can mean intense bitterness, roastiness, aroma, body, or aftertaste. In pharmacology, the meaningful quantities are caffeine concentration and total dose. In everyday experience, strong can mean the coffee felt powerful.
Keeping those meanings separate gives better coffee advice. It prevents dark roast from being mistaken for high caffeine, bitterness from being mistaken for stimulant dose, espresso concentration from being mistaken for total caffeine, and long extraction from being mistaken for the cleanest route to a stronger cup. It also makes room for the psychology of perception without replacing coffee chemistry: expectations and learned associations shape the experience, while roast, dose, brewing, extraction, and chemical composition remain real properties of the beverage.
For a broad guide to beans, drinks, caffeine, brewing, taste, and the sensory psychology of coffee, see Coffee: Beans, Drinks, Caffeine, Brewing, Taste, and Psychology. For the specific relationship among dark roasting, taste, bitterness, and perceived strength, see Dark Roast Coffee: Taste, Caffeine, Bitterness, and the Psychology of Strong Coffee.
Related Articles
For total caffeine dose across beans, roast levels, brew methods, and serving sizes, see How Much Caffeine Is in Coffee? Bean, Roast, Brew, Serving Size, and Why Effects Vary.