Sensory Evaluation of Coffee

Presenter: Ellen Jordan Reidy, from her SCAA presentation

Course Objectives:

To define and understand the benefit of sensory evaluation, the scientific discipline which looks at how we evoke, measure and interpret the characteristics of food and materials as they are perceived by our senses.

To recognize the scientific physiological and psychological elements that affect human’s perception of foods and beverages.

To understand how the human brain receives and processes sensory stimuli and how this impacts our ability to judge and critique the foods we eat.

To recognize “Taste” as a complex array of sensory stimuli that is far more encompassing than the traditional view that the tongue is the only determinant.

To encourage all present to become impassioned “sensuists” (those who rejoice in sensory experience).

What is sensory evaluation?

A scientific discipline used to evoke, measure, analyze and interpret reactions to the characteristics of foods and materials as they are perceived by the senses. Humans are used in much the same way a scientist might use a gas chromatograph.

It is the conscious effort to identify and judge different sensations and components in an object, be it a piece of food, a beverage, or a perfume.

Sensory evaluation encompasses all of the senses. It takes into account several different disciplines but emphasizes the behavioral basis of perception. It involves the measurement and evaluation of sensory properties of food and other materials. Human judges are used to measure the flavor or sensory characteristics of food. In short, sensory evaluation is a very “Gestalt” approach to product assessment.

The human senses

Typically we think of humans as having only five senses. Sensory scientists however, look at eight distinct, although interrelated, senses that are important in measuring and evaluating foods.


Seeing-A product’s appearance. With respect to coffee this seems minimal but if you cupped a quality estate coffee but had a tray of defects before you, the normal palate would be prejudiced. Studies in the wine and beer industry hold this out. Darker colors are associated with more intense flavors even if there is in fact, no difference in the beverages.


Smelling-The aroma or odor volatiles. With gustation, it makes up the Siamese twins of taste.


Tasting- Taste sensations released in water solubles

Tactile Senses

Touch-The item’s texture, mouthfeel, body.

Kinesthetic Senses

Feedback from muscles.


Hearing-Sound when ingested. In coffee, we want to hear slurping so we know we’re getting the coffee back retronasally, but potato chips are the best example of how audition affects sensory evaluation. It is no mistake that potato chips are the size they are, their size requires that your mouth be open while you eat and accentuates the crunching noise. It is also no mistake that they are packaged in crinkling bags to remind you of what you’re eating.

Trigeminal sense

Irritation, pain-Hot/cool sensations. This is a chemical reaction we feel in, for example, the smell of horseradish, the heat of cayenne, the coolness of a peppermint. Tannins in tea and the resulting astringency is a function of the trigeminal sense.


Heat, Cold (Indirect effects of trigeminal sense)

Uses of Sensory Evaluation

Food companies and retail store owners need to evaluate and measure the taste, odor, texture, etc. of foods. A versatile instrument for this is the human sensory system. In the food industry, sensory evaluation is used for:

Grading: Foods can be graded and standardized; this is often done completely by a sensory judgment. We are familiar with this in the wine industry; an expert will designate wines. In the coffee industry we utilize expert cuppers.

Quality Assurance: We need to understand variations in natural products but do not tolerate them in processed foods. If the flavor of a candy is changed, we may reject it. Sensory evaluation is a critical tool for Quality Assurance personnel. It can be used to test for off-flavors, changes due to reformulation, the effects of changes in processing, the effects of storage under various conditions (shelf life studies), the effects of packaging, etc.. In coffee, we need to understand the scope of natural variation in our product. To discern natural variance in new crop vs. past crop coffee or to want to distinguish new crop acidity from possible taint. If you are going to look at changes in your business in any part of the process, from growing to packaging, you’ll want to use sensory evaluation to note differences in the final product.

Correlate Sensory & Chemical/Physical Properties: What specific characteristics in an item give it its taste and smell and are there ways we can manipulate these? (e.g. What are the chemical changes that take place when a wine matures? Which ones affect the flavor? Can they be accelerated?)

Marketing: Sensory information can be vital in making marketing decisions. Data is needed about product preferences, product optimization, consumer acceptance, etc. There is a difference between what you do to assess product quality and process and what you do to look at consumer’s preferences. You never want to use trained experts to predict consumer behavior because by virtue of their training they are no longer reflective of the general population.

Product Development: Introducing new products (e.g. alternative post-harvest treatments for fresh fruits and vegetables; new convenience foods; healthier foods; new ways of packaging, etc.) are good examples of why we need sensory evaluation.

Sensory Evaluation is not just used in he food industry, it is applied to cosmetics, perfumes, tobacco products, animal foods, and cleaning products. There are lots of areas where research is used: developing a new car smell product for used car dealers; a fresh-baked cookie air treatment product for Realtors to use when showing homes; fresh bread aerosols for markets, malls putting pizza aroma through air ducts to draw people to food courts.

If we are going to use humans as flavor measurement instruments we must understand how the sensory system works, how the brain processes information and how the human gives output.

The Human Brain

Not only a re all of our senses of different acuities, (individually and collectively) but the manner in which our brains process information and stimuli plays a critical role in how we understand our senses. All of us brings a different experience to the table.

Most people think of the mind as being located in the head. The latest physiology findings suggest the “mind” travels the whole body on caravans of hormones and enzymes busily making sense of the compound wonders we experience. We aren’t even cognizant of everything taking place.

Our brain has over 1 trillion connections from which it can simultaneously be asked to process millions of sensory stimuli. How do we ever handle it all?

Data Compression: To protect the brain from being bombarded and overloaded, information is compressed and shards of information are fed to the brain like microscopic pieces of a jigsaw puzzle. When enough pieces assemble, the brain says “dog or “chair” This may happen before the entire object is visible. Food perception provides a similar example: A certain pattern of tastes, smells and texture may immediately be recognized as “cheese,” but upon request we can break out our assessment into several taste, smell and texture components.

Adaptation: A change in sensitivity to a stimulus due to continued exposure. (e.g. we will smell paint when we immediately enter a freshly painted room but if we stay there we will soon not notice the smell, or if we put our foot in hot water and don’t move it we will soon not notice the heat, but upon movement it will seem hot again.) This is an important but unwanted effect in sensory evaluation.

Sensory Adaptation

Time-intensity (TI) is a quantitative measure than sensory scientists use to determine how long it takes until adaptation sets in. (e.g. salt water solution) We avoid adaptation in eating and drinking by changing stimuli. During eating or drinking, tongue movements which result from chewing and swallowing are essential because they help to avoid complete adaptation. Artificial sweeteners are often gauged by how much longer the sweetness taste lingers in your mouth than sugar.

Errors that can occur in sensory evaluation

Stimulus error: when irrelevant criteria such as the style or color or the container (or the product itself) influences the observer. e.g. Wine bottles with cork and screwtop on the same product will get differently assessed because of the closure method.

Expectation error: Information given with the sample may trigger preconceived ideas. You usually find what you expect to. e.g. given increasing concentrations of sugar/water solution five cups in a row, the sixth cup will still be rated as sweeter even if it has a lower concentration.

Enhancement: the effect of the presence of one substance/stimuli increasing the perceived intensity of a second substance/stimuli.

Error of habituation: You should taste different things all the time.

Mutual suggestion: The response of a panelist/taster can often be influenced by other panelists. Vocalizing an opinion should be prohibited (and the testing area should be free from noise and distraction).

Capriciousness vs. timidity: Some people tend to use the extremes of any scale thereby exerting more than their share of influence over the panel’s results. Others tend to stick to the central part of the scale and to minimize the difference between scales. This effect can occur when you ask for an honest response in front of an authority figure, and can minimize objectivity and honesty.


Contrast effect-presentation of a sample of good quality just before one of poor quality may cause the second sample to receive a lower rating than if it has been rated alone.

Group effect- one good sample presented in a group of poor samples will be rated lower than if presented on its own. This effect is the opposite of the contrast effect.

Error of central tendency-samples placed near the enter of a set tend to be preferred over those at the ends. In triangle tests, the odd sample is detected more often if it is in the middle position.

Pattern effect-Panelists will use all available clues and are quick to detect any pattern in the order of presentation.

The Gustatory Sense: Taste

Gustation is a chemical sense. It involves the detection of stimuli dissolved in saliva by the taste buds. While located primarily on the surface of the tongue, taste buds are also found on the soft palate, tonsils and upper 1/3 of the esophagus.

Taste has long occupied the minds of scientists both ancient and modern, but little progress was made until the invention of the microscope.

17th century-Italian scientist Marcello Maphigi recognizes papillae on the tongue were organs of taste.

19th century-(1867) Two German scientists described how tiny structures embedded in and around the papillae on the tongue were the actual mediators of taste.

What are taste buds?

Each papilla (round volcano-like structure) contains 250 -270 taste buds, or a total of over 10,000 taste buds in the average human. Taste buds are minute…at least 60-70 can fit on one period on a normal typed page. Since these mounds of overlapping taste cells look like the petals of a flower, they were named “tastebuds.”

Taste buds are in a constant state of flux. Although they seem to us to be of unchanging composition, all 10,000 taste buds are shed and regenerated every 10 days. This regeneration slows down after age 45.

The tongue is like a kingdom divided into principalities by sensory talent. There are specific areas on the tongue in which the receptor cells more keenly note certain taste characteristics. Western civilization recognizes only 4 basic tastes: Sweet, Sour, Salt, and Bitter. The Japanese add a 5th taste they call Umami for monosodium glutamate (MSG).

What we taste varies greatly. Humans detect tastes at the following concentrations:

Sweetness: 1 part in 200

Saltiness: 1 part in 400

Sourness: 1 part in 130,000

Bitterness: 1 part in 2,000,000

This high acuity for bitterness may be an evolutionary defense mechanism that keeps us from swallowing poisons.


What is a sensory threshold? Not only do our tastes have different acuities but also different thresholds. Sensory thresholds are the limits of an individual’s sensory capacities.

There are four types of sensory thresholds, which if you are tasting a cup of water with some added substance such as salt or sugar may be described as such:

    • Absolute threshold

-you recognize there is some additive.

    • Recognition threshold

-you can name sweet/salty, etc.

    • Difference threshold

-How much of a stimulus you need thereafter to make a difference.

    • Terminal threshold

-Above some level at which you will no longer taste it anymore.

What is the effect of age on taste?

There is a significant decline between the ages of 74 and 85 years of age in the density of the villate papillae. The total drops to about 50% of normal adult total. Therefore it takes a higher intensity of taste to produce same level of sensation. Bitter shows the greatest decline while sweet acuity shows little loss.

Practice makes Perfect

Our individual ability to taste (and to smell) reveals very different acuities between all of us. Through repeated use, a ten-fold increase in sensitivity has been confirmed. You are definitely more able to discriminate as you practice

Olfaction The Mute Sense or “Fallen Angel”

Smell contributes magnificently to taste. Without it, most everything we eat or drink would be dull and lifeless. If one holds their nose when drinking wine, it is said to be like drinking water. Smell hits us faster than taste, it takes 25,000 times more molecules of cherry pie to taste it than to smell it. A head cold by inhibiting smell, smothers taste.

Until the time of the Greeks, there were no hard and fast ideas about the organ of smell and even they were inaccurate and confused about the matter! In 1890, Ramon y Cajal, a Spanish neuro-atomist revealed the olfactory bulb’s role in smell.

Olfactory Bulb

A single cell runs from the olfactory mucosa in the nose directly into the olfactory bulb in the brain. In humans, it is very small ( no larger than a postage stamp), and consists of two lobes of yellowish tissue at the base of the brain. In lower vertebrates, the loves are massive; in sharks they are the brain’s most dominant feature.

The color of the olfactory bulb is determined by heredity.

Humans: light yellow

Cats: mustard brown

Fox: reddish brown

The deeper the shade, the more acute the sense. Animals with the keenest sense of smell tend to walk on all fours with heads close to the ground.

About 95 % of the nasal cavity is unrelated to smelling (it’s more like a large air condition/ air treatment plant). A very small amount of air actually reaches the olfactory bulb. (The exit passage in women is larger for some r
ason). We have to inhale, and increase the velocity of our air intake to smell things. For example, if a person walks briskly past you, you will more likely smell their cologne because of the increased air movement. Sniffing increases the air velocity by 3-4 times. The lightest molecules travel farthest. Large sluggish molecules (candle wax) have less smell than lighter molecules (lavender, violet petals).

Inside the Olfactory Membrane

Humans possess approximately 10 million olfactory receptor cells. Each receptor end is a swelling, or knob with approximately 5 hairs (cilia). Unlike neurons in the brain, if damaged the receptors will regenerate. All 10- million will regenerate every 4-5 weeks.

Powers of discrimination

It is a common misperception that humans have a poor sense of smell. There are two facets to olfactory sensitivity, acuity and discrimination. It is true that we are abysmal at acuity judged against other animals. For example, look at the following thresholds for acetic acid (rancid, sweaty odor). Human threshold: 50 million, million molecules/cubic centimeter air. Dog threhold: 500 thousand molecules/cubic centimeter air. Dogs perceive this odor at 100 million times lower concentration than man.

BUT, we are remarkable discriminators. Trained professionals (i.e. perfumers) distinguish thousands of odors and retain memory from session to session. Helen Keller could determine your occupation when you entered the room by your smell. Blind people can commonly recognize visitors by their smell. Unlike the eyes and ears the nose is not triggered by energy (which has no mass). The nose is triggered by pieces of matter which have mass. Once a molecule has fired a response it must be disposed of and that takes a little time. It takes about 2 seconds to inhale, and 3 to exhale. To avoid adaptation, we smell in short bursts with pauses, or pass from nostril to nostril to prevent odor fatigue.

Not everything has a smell. Stone, glass, steel, do not release molecules that evaporate at room temperature. Only substances volatile enough to spray microscopic particles into the air have aroma. Heating a substance increases its smell, e.g. cabbage. Weightlessness in space makes astronauts lose their sense of smell and taste.

Medical/Aging considerations:

Smell diminishes with age like many other senses, more so than taste. Smell can also be lost due to medical reasons: cold, allergies, tumor, epilepsy, brain injury, Alzheimer’s.

Marcel Proust Effect

Marcel Proust had an experience dunking a piece of toast in tea and milk, it took him back to his grandmother’s and inspired him to write Remembrance of Things Past Certain odors can bring on torrential floods of memory. Examples might be: first baseball mitt; first doll; a baby’s head; your child, parent, grandparent, lover; Vick’s VapoRub, in which you have a flood of memories associated with a particular aroma.


Our perception of taste is the result of many sensations: smelling, tasting, texture, sound, temperature, appearance, chemical pain; as well as cognitive factors such as knowledge and expectation.