Instant coffee: Wikis

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Spray dried instant coffee

Instant coffee is a beverage derived from brewed coffee beans. Through various manufacturing processes the coffee is dehydrated into the form of powder or granules. These can be rehydrated with hot water to provide a drink similar (though not identical) to conventional coffee. At least one brand of instant coffee is also available in concentrated liquid form.

The advantages of instant coffee are speed of preparation (instant coffee dissolves instantly in hot water), less weight and volume than beans or ground coffee to prepare the same amount of drink, and long shelf life; coffee beans, and especially ground coffee, lose flavour as the essential oils evaporate over time. Lack of cafestol in instant coffee might also be considered an advantage, because the compound is largely responsible for raise in cholesterol levels, which is associated with regular coffee drinking.

Although it has a long shelf life, instant coffee quickly spoils if it is not kept dry. Instant coffee differs in make-up and taste from ground coffee. In particular, the percentage of caffeine in instant coffee is less, and bitter flavor components are more evident. The lowest quality coffee beans are often used in the production of instant coffee (the best beans are usually kept to be sold whole) and sometimes other unwanted residues from the harvest are used in the production process[citation needed]. Some products, such as corn, are also used to make the coffee condense more quickly (some manufacturers practice this)[citation needed].

Instant coffee is commercially prepared through vigorous extraction of almost all soluble material from ground roasted coffee beans. This process naturally produces a different mix of components than does conventional brewing.

Contents

History

Instant coffee was invented in 1901 by Satori Kato, a Japanese scientist working in Chicago. Kato introduced the powdered substance in Buffalo, New York, at the Pan-American Exposition.[1] George Constant Louis Washington developed his own instant coffee process shortly thereafter, and first marketed it commercially (~1910). The Nescafé brand, which introduced a more advanced coffee refining process, was launched in 1938.

High-vacuum freeze-dried coffee was developed shortly after World War II, as an indirect result of wartime research into other areas. The National Research Corp. was formed in Massachusetts as a process-development company employing high-vacuum technology. It developed high-vacuum processes to produce penicillin, blood plasma and streptomycin for US military use. As the war ended, NRC looked to adapt its processes for peacetime uses. It formed Florida Foods Corp. to produce concentrated orange juice powder, and originally sold its product to the United States Army. That company later changed its name to Minute Maid, and decided to produce concentrated orange juice instead of powdered OJ. The company then applied its high-vacuum expertise to the production of instant coffee. A plant was erected in Cambridge, Massachusetts in 1949 to perfect this process, and by 1951 the product was well-developed. The plant was incorporated under the name Holiday Brands; it was later re-absorbed into the Minute Maid fold of companies.[2]

Use

One advantage of instant coffee is its simplicity of preparation. It is virtually impossible to accidentally spoil the product during the rehydration process, and simple instructions are printed on the back of typical instant-coffee packaging.

Instant coffee is available in powder or granulated form contained in glass jars, sachets or tins. The user controls the strength of the resulting product, by adding more or less water (for a weaker or stronger brew). Too strong a brew may spoil the intended flavor and produce what some describe as an unpleasant "metallic" taste.

Instant coffee is also convenient for preparing iced coffee like the Greek frappé, which is popular in warmer climates and hot seasons.

In some European countries such as Spain, instant coffee is commonly mixed with hot milk instead of boiling water

Production

As with regular coffee, the green coffee bean itself is first roasted to bring out flavour and aroma. Rotating cylinders containing the green beans and hot combustion gases are used in most roasting plants. When the bean temperature reaches 165°C the roasting begins, accompanied by a popping sound similar to that produced by popcorn. These batch cylinders take about 8–15 minutes to complete roasting with about 25-75% efficiency. Continuous fluidized bed roasting only takes between thirty seconds and four minutes, and it operates at lower temperatures which allows greater retention of the coffee bean aroma and flavor.

The beans are then ground finely. Grinding reduces the beans to 0.5–1.1-millimetre (0.020–0.043 in) pieces in order to allow the coffee to be put in solution with water for the drying stage. Sets of scored rollers designed to crush rather than cut the bean are used.

Once roasted and ground, the coffee is dissolved in water. This stage is called extraction. Water is added in 5-10 percolation columns at temperatures of 155 to 180°C; this concentrates the coffee solution to about 15-30% coffee by mass. This may be further concentrated before the drying process begins by either vacuum evaporation or freeze concentration.

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Freeze drying

Production freeze dryer

The basic principle of freeze drying is the removal of water by sublimation.

Since the mass production of instant coffee began in post-WWII America, freeze drying has grown in popularity to become a common method. Although it is sometimes more expensive it generally results in a higher quality product.

  1. Agglomerated wet coffee granules are rapidly frozen (slow freezing leads to large ice crystals and a porous product and can also affect the colour of the coffee granules).
  2. Frozen coffee is placed in the drying chamber, often on metal trays.
  3. A vacuum is created within the chamber. The strength of the vacuum is critical in the speed of the drying and therefore the quality of the product. Care must be taken to produce a vacuum of suitable strength.
  4. The drying chamber is warmed, most commonly by radiation but conduction is used in some plants and convection has been proposed in some small pilot plants. A possible problem with convection is uneven drying rates within the chamber, which would give an inferior product.
  5. Condensation - the previously frozen water in the coffee granules expands to ten times its previous volume. The removal of this water vapour from the chamber is vitally important, making the condenser the most critical and expensive component in a freeze drying plant.
  6. The freeze-dried granules are removed from the chamber and packaged.

Spray drying

Spray drying is preferred to freeze drying in some cases because of its economy, short drying time, usefulness when dealing with such a heat-sensitive product, and the fine, rounded particles it produces.

Spray drying produces spherical particles about 300 micrometres (0.012 in) size with a density of 0.22 g/cm³ (ref 2). To achieve this, nozzle atomization is used. Various ways of nozzle atomization can be used each having its own advantages and disadvantages. High speed rotating wheels operating at speeds of about 20,000 rpm are able to process up to 60,000 pounds (27 tonnes) of solution per hour (ref 3). The use of spray wheels requires that the drying towers have a wide radius to avoid the atomized droplets collecting onto the drying chamber walls.

  • Completed in 5–30 seconds (dependent on factors such as heat, size of particle, and diameter of chamber).
  • Moisture content change: IN = 75-85% OUT = 3-3.5%
  • Air temperature: IN = 270°C OUT = 110°C

One drawback with spray drying is that the particles it produces are too fine to be used effectively by the consumer; they must first be either steam-fused in towers similar to spray dryers or by belt agglomeration to produce particles of suitable size.

Decaffeination

In commercial processes the decaffeination of instant coffee almost always happens before the critical roasting process which will determine the coffee's flavour and aroma processes.

Regulatory context

In the EU, regulations include the following details:

  • Species of coffee bean
  • Geographical origin
  • Processing detail
  • Year of crop
  • Solvents used in decaffeination
  • Caffeine level

Various institutions govern the coffee industry and help to achieve standardisation and also release information to the public.

  • International Coffee Organisation (London)
  • Codex Alimentarius Commission of the UN (Rome)
  • National Coffee Association (New York)

Bibliography

  • Romualdo Verzosa Jr., ed (1993). Encyclopedia of Chemical Technology, volume 6 (4th Edition ed.). John Wiley & Sons. ISBN 0-471-52674-6. 
  • Masters, K (1991). Spray Drying Handbook (5th Edition ed.). Longman Scientific & Technical. ISBN 0-582-06266-7. 
  • John J. McKetta, ed (1995). Encyclopedia of Chemical Processing and Design. Marcel Dekker Inc. ISBN 0-8247-2604-9. 

References

  1. ^ Carlisle, Rodney (2004). Scientific American Inventions and Discoveries, p.355. John Wiley & Songs, Inc., New Jersey. ISBN 0471244104.
  2. ^ Chemical & Engineering News, 2 February 2009, "Freeze Dried Coffee", pp. 4-5

External links


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