Instant coffee
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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 but different than 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.
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 to 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].
"Organic" instant coffee is available, which comes from beans grown and processed in special facilities without using synthetic chemicals.
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.
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[edit] History
Instant coffee was invented in 1901 by Satori Kato, a Japanese scientist working in Chicago, United States. 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.
[edit] Use
One of the advantages of instant coffee is its simplicity of preparation compared to other forms of coffee. 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 can come in either powder or granulated form contained in glass jars, sachets or tins. Powder and granules are generally preferred by both producer and consumer because of the ease and time for dissolving in hot water. It is up to the user to control how much is used; large amounts will produce stronger, thicker coffee whereas small amounts will produce a light coffee. Too much coffee may spoil the intended flavor and produce what some may 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.
[edit] Production
Below are general outlines for stages in modern production of instant coffee:
[edit] Roasting
The green coffee bean itself has no desirable taste; it must first be roasted to bring out flavour and aroma. The process for this is the same for regular coffee as it is for instant coffee.
Rotating cylinders containing the green beans and hot combustion gases are used in most roasting plants. When the bean temperature reaches and exceeds 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, it also operates at lower temperatures which allows greater retention of the coffee bean aroma and flavor.
[edit] Grinding
This next step reduces the beans to a size of anything between 0.5 and 1.1 mm in order to allow the coffee to be put in solution with water for the drying stage. Sets of scored rollers specially designed to cut rather than crush the bean are used.
[edit] Extraction
Once roasted and ground, the coffee must be put into solution with water. This stage is called extraction. Generally water is added in 5-10 percolation columns at temperatures of between 310 and 360 °F (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.
[edit] Drying
This step is a very important one and two different methods are used in plants all over the world, freeze and spray drying, each has its own advantages and disadvantages.
[edit] Freeze Drying
The basic principle of freeze drying in the process for producing instant coffee 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 very common method. This is often because, although it is frequently more expensive than other methods of drying, it generally results in a higher quality product.
- The Freeze Drying Process
- Agglomerated wet coffee granules are frozen. For instant coffee this is a very important stage. Freezing too fast leads to large ice crystals and a very porous product and can also affect the colour of the coffee granules.
- Frozen coffee is placed in the drying chamber, often on metal trays.
- 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.
- 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.
- Condensation - the previously frozen water in the coffee granules expands to 10⁷ its volume, the removal of this water vapour from the chamber is vitally important, making the condenser the most critical and expensive components in a freeze drying plant.
- The freeze dried granules are removed from the chamber and packaged.
[edit] Spray Drying
This method of drying is preferred to freeze drying in some cases because of its cost effectiveness, short drying time, usefulness when dealing with such a heat-sensitive product, and the fine, rounded particles it produces.
Spray drying produces spherical particles of size roughly equal to 300 µm with a density of 0.22 g/cm³ (ref 2). To achieve this, nozzle atomisation 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 t) of solution per hour (ref 3). The use of spray wheels requires that the drying towers have a wide radius to avoid the atomised droplets collecting onto the drying chamber walls.
- Typical Spray Drying Characteristics
- 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 Temperatures, 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.
[edit] Decaffeinated instant coffee
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 characteristics.
Modern processes use one of two common decaffeination methods, solvent extraction or water extraction.
[edit] Solvent Decaffeination
The most commonly used solvents are trichloroethylene, methylene chloride or a similar chlorinated hydrocarbon. More recently, supercritical carbon dioxide has been used as an alternative solvent to the more hazardous chlorinated hydrocarbons.
In order for solvent decaffeination to function additional moisture is required in the coffee bean. The method for introducing this moisture does not matter -- the importance is the water content of the bean, and typically anything between 18% and 55% is sufficient. The moisture is required to soften the cellular structure of the bean.
- Basic steps of solvent decaffeination
- Steaming of coffee beans for 30 minutes at 230 °F (110 °C).
- Increase of coffee bean moisture content to above 40%.
- Beans flow through extractor columns with solvent at temperatures between 120 °F and 250 °F (50 °C to 120 °C). Caffeine is removed from beans.
- Decaffeinated beans are "steam stripped" of solvent for 90 minutes.
- Decaffeinated beans are removed from extractors and dried.
- Caffeine rich solvent is recycled to be used in step 2.
[edit] Water decaffeination
Water extraction of caffeine was first patented in 1941 by General Foods. Its claimed advantages are:
- Higher extraction rates
- Caffeine recovery by this method produces a purer product
- Less heat treatment of the coffee bean
- No direct solvent contact with the bean
This method takes about 8 hours, considerably longer than solvent decaffeination; however it does seem to produce a better quality end product.
The basic method involves the use of a water extract of green coffee beans in a battery of columns in contact, countercurrently, with green beans. As contact is made the green beans preferentially absorb water. The solid content of the water extract of green beans doubles (from 15% to 30%) as caffeine is taken up. During the 8 hour process about 98% of the caffeine is removed, which is comparable with the solvent extraction method. The decaffeinated beans, now 58% moisture by weight, are washed and dried.
[edit] 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)
[edit] Bibliography
- (1993) in Romualdo Verzosa Jr.: Encyclopedia of Chemical Technology, volume 6, 4th Edition, John Wiley & Sons. ISBN 0-471-52674-6.
- Masters, K (1991). Spray Drying Handbook, 5th Edition, Longman Scientific & Technical. ISBN 0-582-06266-7.
- (1995) in John J. McKetta: Encyclopedia of Chemical Processing and Design. ISBN 0-8247-2604-9.
[edit] External links
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