中文 ｜English

 

Green Coffee

Uniformizing Coffee Beans

To appreciate how a small amount of impurity (whether it is a defective coffee bean, or a foreign piece of metal) can influence the taste of the resulting coffee beverage it is constructive to see how many distinct classification steps are required to uniformize and elevate the grade of coffee beans:

• Growing fruit on a healthy shrub in a suitable environment without insect or disease damage.
• Harvesting only ripe healthy fruit from the branches for the shrub, and not picking green, overripe, dried, fallen, or otherwise abnormal fruit.
• Density classification: water floatation of freshly picked fruit in canals (to float off immature cherries called stinkers which remain whitish) and to allow stones, metals and heavier to sink.
• Pulping machine tearing off the skin of the cherry without damaging or nipping the seed.
• Properly fermenting the fruity mucilage so that no remaining fruit on the seed can consequently cause anomalous tastes and defects in the beans.
• Prompt drying of the fermented and washed beans in the sun. Warm air bean drying machines can be used in the final stages of drying to avoid uncontrolled fermentations, overheating, over- or under-drying, mold growth, etc.
• Hulling: Removing the skin or parchment layer from the beans after drying.
• Classifying the cleaned beans by size, shape and density, rejecting broken, deformed and abnormal.
• Color sorting: Removing beans of abnormal colors (black, white, or red) from cleaned green (or roast) beans.
• Removing foreign matter like sticks, stones, wires, dust, dirt, etc.
• Density classification of beans in air levitation and vibrating conveyor tables.
• Order classification of green coffee beans. There must be no moldy fermented or foreign aroma. Also use of bean hand feel and bean appearance guides.
• Classifying for uniformity of roast color development: rejecting burnt or unroasted beans.
• Classifying green beans by age of crop and source, as well as time and conditions in shipment.

In the growing countries, having uniformized, purified, and graded the coffee beans to the above extent, one seriously considers the mixing of lots. In blending lots of coffee beans, as with mixing food products, the addition of a poorer grade to a better one, will invariably downgrade the mixture closer to the qualities of the poorer grade.

(Source:：Coffee Technology by by Michael Sivetz, Norman W. Desrosier)

 

 

---

Roast Coffee

Coffee Bean Properties During Roasting

Roasting is the step relating to coffee aroma and flavor development in the processing of green coffee beans. The aroma and flavors developed are characterized by the type of green coffee. The degree of roast is related to the type of green coffees being processed and the market or disposition of the roast coffee. The manner in which the chosen degree of roast is attained is dependent on the type of roasting equipment used. Although green coffees vary in chemical and physical properties, the chemical and physical changes they undergo during roasting are similar even though they vary in degree. Roasting of green coffee beans is essentially a process of exposing the green coffee beans to a warming process that is sufficiently fast to drive off the free and bound moisture of the bean and the dried bean residue is heated to more than 400F ( 200C). At about this temperature, pyrolysis, or thermal decomposition and chemical change, occurs within the bean. In a fraction of a minute exothermic (heat liberating) chemical reactions occur. The bean temperatures rise to 392 to 410 F (200 to 210 C) with an accompanying dry bean weight loss rising from 4 to 6 percent. With a green bean starting moisture of 12 percent, this is equivalent to a 16 to 18 percent total roasting loss. The higher the percent loss, the darker the roast color. The brown color development of the bean occurs during this period of rapid loss in weight. Most of the sucrose is altered and most of the swelling of the bean (to almost twice its original volume) also occurs during this period, with the simultaneous revelation of the chaff at the bean crevice.

Influences of Degree of Roast

Light roasts have more acidity, and hence are more suited to areas where alkaline waters are used. Since lower grade coffees have their poor flavor characteristics more readily revealed in light roasts, it is usually better to roast these coffees dark so as to drive out most of the characterizing volatiles. From the foregoing discussion, the advantages of blending roasted coffees are self-evident. Habituation and local taste preferences often govern the degree of roast. In cities this is usually darker than average, as is indicated by the expression, "city roast." This type of roast usually used in the preparation of roast coffees for soluble coffee manufacture. Since more carbohydrates are made water soluble in plant percolation than in brewing at home, the additional carbohydrate flavor needs to be balanced off by a deeper roast.
There is a relationship between visual color of the roast bean and the percentage of roast loss. A light to medium cinnamon-colored roast which is just within the palatable range would have about a 14 percent loss; a fully developed roast of deep brown but not blackish-dark would have about a 15 1/2 percent loss; a high roast which is dark brown with tinges of black would have about a 17 percent loss, and is the darkest usually used in the United States. However, specialty roasts, such as the Trench, are very dark brown with some oil slicks on the bean surfaces, and have about an 18 percent roast loss; the Italian roast is extremely dark brown at about a 20percent loss. In all cases, it is assumed that the green coffee contains about 12 percent moisture.

3 Step Process: Drying, Pyrolysis & Cooling

Imported coffee beans usually have about 12 percent moisture, and as the beans are exposed to high roasting temperatures ranging from 500 to 800 F, the moisture is evaporated as the beans warm up.
The actual time, temperature and color effects will vary some what with method of roasting, time cycle, type bean, initial moisture, rates of heat transfer, etc. but the general description of what occurs, holds. What is really significant in all cases of roasting is that a great deal of heat is released from the bean, being triggered at near 400F, and is considered to be pyrolysis or chemical decomposition of sucrose.
oasting is often accompanied by popping sounds and oily smoke, which is mostly water vapor but with a blue color. As soon as the desired bean color is reached, the beans must be removed from the heated gases and be promptly and positively cooled by ambient beans, with hardly any water being absorbed by the beans if the water spray is light. Cooling of the roasted beans stops the pyrolysis reactions. Holding roasted beans hot downgrades their flavor.

(Source：Coffee Technology by by Michael Sivetz, Norman W. Desrosier)

 

 

---

Grinding

The roast bean properties have a great deal to do with grinding results. Beans cannot be ground directly after roasting as they are too soft and would be crushed, flattened, and scarred. When the beans are cool, hard, and brittle, they may be ground. Beans are physically softer when they have several percent moisture; they are most brittle when air cooled without moisture addition. Light roast coffees are tenacious, pliable, and tough; they do not break down as easily as hard, brittle, dark roasted beans.
Ground coffee readily absorbs atmospheric moisture and is a good desiccant. In evaluating the nature of roast coffee during the grinding process, it is desirable to consider the bean properties, namely: moisture content, roast, hardness, pliability, strength, resilience, fiber, brittleness, particle size, and flavor development.

(Source：Coffee Technology by by Michael Sivetz, Norman W. Desrosier)

 

 

---

Brewing

(Also check our demonstration video in Brewing)

Brew Taste

Brewing can be considered a personal taste adventure. The majority of people brew coffee to make an acceptable to pleasant brew for others. Not everyone's taste preference can be pleased, nor to the same degree. But the majority of persons served can be given an acceptable cup of coffee.
There are some generally accepted rules about the proper way to brew a good cup of coffee. It is the lack of good quality coffee taste experience and the numerous variables in brew preparation and coffee use that confuse the consumer. This gives restaurateurs or roasters an opportunity to claim that their coffee is "best" or "good."

Five Essentials of Good Coffee Flavor

To control the five essentials for preparing a cup of really good coffee takes many talents and skills. One must know the quality of the coffee used: a brand name does not necessarily ensure coffee quality. One must also know something about keeping coffee fresh and be able to evaluate the packaging. One must determine whether the water quality is influencing the cup flavor. For the taste desired, economy must be secondary and the right water-to-coffee ratio must be used. The brewing method must be fast and thorough, yet not exhaustive. The serving must be prompt. In a fine coffee shop, the green beans are chosen, roasted on the day of use, ground just before extraction, brewed in minutes if not in seconds, and served promptly in suitable cups.

• Coffee Quality- Admittedly, experience can tell a person what a good tasting coffee is. However, to be absolutely sure of the basis of choice, the coffee type by variety (Arabica or Robusta) and origin (mild or Brazilian) must be known. Then the geographical (political) source, altitude of growth, quality of processing of green coffee beans (fermentation, drying, cleaning, grading, storage), age, purity (freedom from foreign matter), bean size, and moisture ought to be known. Usually most of this is not possible, so the taste and aroma must become the final basis of judgment.
• Package- Reports have been cited here and elsewhere that coffee can be held fresh indefinitely in a vacuum can, vacuum bag, inner gas filled container, etc. In every case, some oxygen is left in the container, and this oxygen proceeds to react with the key aroma and flavor factors in the coffee. Hence, some staling occurs within every package. Considerable staling occurs after the package is opened, so put it another way, the best vacuum packed coffee is never as good in flavor as the day it was placed in the can. In fact, the process of drawing a vacuum about the coffee particles draws flavor away. The storage of coffee before it enters the can exposes it to staling. Hence, the coffee house that roasts and grinds its coffee just before use has a real flavor advantage over the commercial vacuum pack. Some evaluations state that ground coffee stays fresh up to three or more weeks. According to any coffee taster, this is absurd. The ground coffee may be acceptable to a less critical and/ or a less informed consumer who uses milk and sugar and possibly not the best brewing and serving methods. Hence, the freshness of the roast coffee's volatile flavors and their abundance are important factors from the moment of grinding until brewing, and package protection can play a vital part in this time interval.
• Water Quality and Water-to-Coffee Ratio- Since water constitutes 99 percent of the coffee beverage, its impurities and quality can markedly downgrade coffee brew flavor. Water may be hard, alkaline, or brackish, or have organic matter, chlorine, odors, gases, or metal impurities. It is an error to make weak coffee, because this type of extraction brings out the undesirable flavors. An axiom in brewing is, in case of doubt make the cup stronger. A frequent error is not measuring water nor coffee at all, so that control is lost entirely in this variable. ( Water to Roast Coffee Ratio- In the English weights and measures system, the water to coffee ratio of about 2.00 to 2. 25 gal of water per pound of roast coffee is recommended for the best brew flavor. This corresponds in the metric system to a water to coffee ratio of 16.7 to 18.8 liters per kilogram.
  Water Absorption- Roast coffee grounds hold twice their dry weight of water, plus whatever water does not drain off completely from the interstices.)
  
• Brewing Method- Numerous methods have been cited: some of the most popular home and commercial methods destroy the aromatic properties of the best coffees. These include boiling, preparation of large batches that cannot be rapidly served, urn extraction, mixing an old batch with a fresh batch, and percolation, which intimately mixes coffee extract brew with air and spent coffee grounds. Essential to good brewing technique are speed, a reasonable extraction yield, and solubles concentration. Most brewing methods take five or more minutes. Channeling of rinse drip, percolate, or wash does not uniformly extract the coffee solubles. Fine grinds are seldom used. In fact, fine grind is difficult to get in many United States retail stores. Some of the newer pressurized extraction methods through granular coffee beds, not slurries, give fast, uniform extraction. Some methods such as urn, drip, and percolation cannot provide uniform flow through the granular bed.
• Serving Method- If all the foregoing essentials of preparation have been perfect, it is not uncommon to find the brew boiling or near boiling for many minutes on a pot heater. Admittedly, adding sugar and milk or cream covers up the bitterness of the coffee. But if really good coffee is desired, it is best enjoyed black. Cleanliness of utensils is, of course, essential for brewing and serving but is "economical" practice. The espresso method, which brews one cup at a time, offers some very desirable features.

Other Critical Factors ：

Time Factor- The most important point regarding the processing of coffee, whether it is roasted coffee, instant coffee power, or brewed coffee beverage, is that processing must be done quickly. Coffee aroma and flavor are very delicate and transient phenomena. Elusiveness is part of their attractiveness. They can be captured only momentarily (unless one stands downwind of the roaster or grinder) at the consumer level. The aroma and flavor are fragile and fleeting. The water must be of good quality. The apparatus must brew with speed and reproducibility. The brew must be delivered and consumed promptly. Any gap in this timing sequence destroys the end result and the pleasure and satisfaction the brew ought to bring. Reducing the brewing process to a set of mechanically reproducible steps, automatically carried out without human interruption until the brewed beverage is dispensed attains the desired goal. This already has been achieved to varying degrees in commercial brewing units which control times, temperatures, and proportions accurately.

Brewing Notes ：

The following comments are listed as being pertinent to the preparation of good tasting coffee beverage from roast and ground (R&G) coffee:

• The coarser the coffee grind the less efficient is the water extraction and the yield of coffee flavor and solubles.
• Any brewing method that involves holding the hot coffee beverage will contribute to its deterioration in flavor. Household percolation is a poor method of preparing flavorful coffee beverage. In fact, household coffee percolation drives off the coffee aroma by steam distillation and leaves a strong tasting solubles residue
• Cleanliness of the equipment, purity of the water, the grind, and freshness of the roast coffee as well as the quality of the coffee, the weight ratio of coffee to water, and the time of contact will bear on the flavor of the coffee beverage prepared. The Coffee Brewing Institute Standard is to prepare 40-5-fl oz (150 ml) cups of brew per pound of roast coffee. In Latin America 30 cups per pound are common with a darker roast, finer grind, heavier blend, and different modes of brew preparation.

Chances for Consistently Brewing a Flavorful Beverage

To obtain a clean flavored fresh cup of brewed coffee at the right concentration and temperature containing most of the natural coffee aroma and flavor is not simple. With ten or more preparation variables, an uneducated approach offers only a very small chance because of the following compounding factors. However, recognition and control of these contributing factors can raise one's chances considerably for preparing a tasty coffee beverage.

• Mass marketed and low priced coffees do not offer the best coffee quality or flavor. Brand name tells the buyer nothing about the true nature of the coffees used.
• Buying or preparing freshly roasted coffee beans is important.
• Vacuum packed cans of commercial coffee are only partly fresh; staling it rapid after one opens the can. Buy only 1 lb at a time.
• The average user must acquire more knowledge about brewing and coffee to make a tasty beverage consistently.
• Water quality over large geographic areas noticeably downgrades coffee flavor.
• Guessing weights of coffee and water; hence, their ratio is unscientific and not reproducible, leading to dilute and watery preparations.
• Pumping percolation does not get much coffee flavor in the cup, but plenty of aroma in the kitchen. Urn coffee, even if prepared reasonably well, will taste harsh and acidy after being held hot for an hour or two before serving.
• Timing in any brewing process must be reproducible.
• Then there are the factors like cleanliness of equipment, materials of construction, flavor contributing filter papers or rubber gaskets, etc. that are important.
• Have a scale of values. Not recognizing these circumstances, one cannot expect to receive more than one cup in ten that will be a pleasure, perhaps three or four cups in ten that will have acceptable taste, and the rest will not taste good. The brew may then be consumed with milk or cream and sugar, but not with much joy. However, taking precautions about these factors can give most coffee brews really acceptable to enjoyable flavor.

What to look for when you taste:

( A Connoisseur's Companion by Claudia Roden )

• Sweetness is due to the sugar content
• which caramelizes on roasting.
  
Acidity is derived from a complex of compounds misnamed "caffetanic acid". Coffee low in acidity tastes smooth, soft and mellow but some acidity is desirable as it adds sharpness and life. Coffee tastes flat with out acidity.

• Bitterness is present naturally in some beans. It is also due to decomposition products formed during roasting. These types of bitterness are considered appealing and have their following. But the bitterness that is the result of chlorogenic acid and the soluble mineral content of the bean when there is over-extraction in the brewing process is unpleasant.
• A neutral taste is prized particularly for its blending qualities and capacity to marry well with other tastes.
• Aroma or fragrance is the gases, products of aromatic oils, released by roasting. The best coffees have two or three times more aromatic oils than others. Some aromas are delicate and fleeting, some are complex and powerful. They are experienced as part of taste.
• Body is a quality characterized by a thick, heavy feel and lingering rather than evanescent taste.

(Source：Coffee Technology by by Michael Sivetz, Norman W. Desrosier)

 

 

---

Physiological Effects of Coffee

Body Influences

People's bodies are different. The coffees they drink are different. This suggests, therefore, that there might be a wide range of physiological reactions obtainable from food and drink, including coffee. A body's reaction to coffee falls into many gray areas. The body is in a different state under different conditions:

• when one wakes up,
• after a hard day's physical or mental work,
• after dinner,
• late in the evening,
• after much outdoor exposure to cold and wind.

People do suffer from sleeplessness, nervousness, intestinal discomfort, heart stimulation and other effects after drinking one or two cups of coffee. On the other hand, it is presumptive to say that this is only 1 percent of the drinkers, although no such scientific measurement has been made. It is well known from personal experience that "excessive" coffee drinking can cause all those things mentioned. "Excessive" can be one cup for some, two cups for others, and three cups for people in general. Here again, we depend on what the people are doing and where they are. People that habitually drink coffee require a larger dose for stimulation. This is because they develop a tolerance to the drink. Whereas, a non-coffee drinker will get a "stimulating reaction" from a single cup of coffee.
Individual tolerances to dosages without obvious symptoms vary with age, sex, physical condition, environment, and other factors. Heretofore, caffeine has been considered the exclusive activating ingredient. But now the chemicals formed from roasting are known to cause body effects. Coffee oils, fatty acids, (hydrolyzed) cellulose components in coffee beverages held hot for many hours may also cause body discomforts.

The following cogent reasons for drinking coffee are genuine for many people:

• Stimulates the brain
• Speeds thought processes
• Increases idea association
• Improves memory recall
Result: a more rapid and clearer flow of thoughts.
• Contributes a feeling of "well-being"
• Counteracts sleepiness
• Counteracts physical and mental fatigue
• Makes one generally more alert
• Relieves headaches (at times migraine)
• Opens blood flow path to brain (dilates some blood vessels)
• Stimulates cortex of brain
• Increases respiration-releases poisons/ takes oxygen
• Stimulates urination/ or bowels
• warms the body through increased blood circulation
• Cools the body through increased blood circulation and respiration, accompanied by increased perspiration.
• Stimulates the heart to pump more blood due to reduced arterial restrictions.
• Ordinarily pulse rate not affected much
• Ordinarily blood pressure not increased (due to dilation of blood vessels)
• Increases stomach acid secretion-desirable to digest food (undesirable for ulcerated persons).
• Increases bile secretion of gall bladder, assists fat digestion.
• Counteracts alcohol and other drugs' depressing symptoms. Coffee after cocktails or after the hangover increases the respiration rate by stimulating medullary center.

(Above informaiton except the section "What to look for when you taste" is from the book "Coffee Technology" by Sivetz Desrosier. All right is reserved to its original author.)

(Source：Coffee Technology by by Michael Sivetz, Norman W. Desrosier)