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Instant coffee is a beverage derived from coffee. Through various manufacturing processes the coffee is dehydrated into the form of either powder or granules. These can be rehydrated using water that is hot (but never boiling), to provide a drink that most people are happy to accept as 'coffee'. There is also at least one brand of instant coffee available in concentrated liquid form.

The advantages of instant coffee are speed of preparation (no time is required for infusing the coffee – it is ready as soon as the hot water is added) and long shelf life (natural coffee, especially in ground form, loses flavour as its essential oils evaporate over time).

The disadvantages are that instant coffee is easily spoiled if not kept dry and its taste, especially with cheaper brands, is often far from the real thing. Moreover, the lowest quality coffee beans are used (the best beans are usually kept to be sold as whole beans), and sometimes other unwanted residues from the harvest are the raw material for the production of instant coffee. Instant coffee is also distinct from fresh coffee and is commercially prepared through vigorous extraction of almost all soluble material from the ground roasted beans. This process naturally produces a different mix of components than home brewing. In particular, the percentage of caffeine in instant coffee is less, and undesirable bitter flavor components are more present.

Opinions on instant coffee range from "intolerable imposter", through "reasonable alternative", to "better than the real thing." Due to the fact that it was the norm in American homes until the 1980s, some areas of the world see it as a particularly sophisticated beverage. Ironically, instant coffee is the only form of coffee available in certain coffee exporting countries. This may possibly be due to a society's appeal to novelty. In countries where it is popular, it is often referred to as "Café Puro" to the horror of coffee aficionados.

History

Instant coffee was invented in 1901 by Satori Kato, a Japanese scientist working in Chicago. However, it was not marketed commercially until Nescafé launched in 1938. Its popularity soared in post WWII America and today it can be found all over the world.

Use

One of the advantages of instant coffee is its simplicity of use compared to other forms of coffee making. It is very difficult to accidentally spoil the product, and simple instructions are printed on the back of containers.

Instant coffee can come in either powder or granulated form contained within 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 weak coffee.

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

Production

Below are general outlines for stages in modern production of instant coffee:

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 0.5–4 minutes and also operates at lower temperatures which allows greater retention of the coffee bean aroma and flavor.

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.

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.

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.

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
  1. 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.
  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 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 10 times 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.
  6. The freeze dried granules are removed from the chamber and packaged.

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. 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.

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.

Solvent Decaffeination

The most commonly used solvents are trichloroethylene, methylene chloride or a similar chlorinated hydrocarbon.

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
  1. Steaming of coffee beans for 30 minutes at 230 °F (110 °C).
  2. Increase of coffee bean moisture content to above 40%.
  3. 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.
  4. Decaffeinated beans are "steam stripped" of solvent for 90 minutes.
  5. Decaffeinated beans are removed from extractors and dried.
  6. Caffeine rich solvent is recycled to be used in step 2.

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.

Regulatory Context

Instant coffee is not considered a dangerous substance; nevertheless its sale and production are regulated.

In the EEC 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

  1. Encyclopedia of Chemical Technology, Forth Edition, Volume 6, Executive Editor Jacqueline I Kroschwitz Published by John Wiley & Sons 1993. ISBN 0-471-52674-6
  2. Spray Drying Handbook, Fifth Edition, K. Masters 1991. Published by Longman Scientific & Technical. ISBN 0-582-06266-7
  3. Encyclopedia of Chemical Processing and Design. Editor John J. McKetta, Published by Marcel Dekker Inc. 1995. ISBN 0-8247-2604-9
  4. SO MANY WAYS TO MAKE COFFEE
This article is licensed under the GNU Free Document License
It uses material from Wikipedia.

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