Instant coffee, also called soluble coffee and coffee powder, is a beverage derived from brewed coffee beans. Instant coffee is commercially prepared by either freeze-drying or spray drying, after which it can be rehydrated. Instant coffee in a concentrated liquid form is also manufactured. Examples of popular instant coffee brands are Extra, Folgers, Maxwell House, Nescafé and Starbucks VIA.
Advantages of instant coffee include speed of preparation (instant coffee dissolves instantly in hot water), lower shipping weight and volume than beans or ground coffee (to prepare the same amount of beverage), and long shelf life — though instant coffee can spoil if not kept dry. Disadvantages include an inferior taste to freshly brewed coffee.
Instant or soluble coffee was invented and patented in 1890, by Mr David Strang of Invercargill, New Zealand, under patent number 3518. It was sold under the trading name Strang's Coffee citing the patented "Dry Hot-Air" process. The invention was previously attributed to Satori Kato, a Japanese scientist working in Chicago in 1901. Kato introduced the powdered substance in Buffalo, New York, at the Pan-American Exposition. 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 Corporation 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 Corporation 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.
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 powder to the water, ranging from thin "coffee water" to very strong and almost syrupy coffee. A novel way is to use coffee bags, similar to tea bags.
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. Coffee roasting using a fluidized bed only takes from thirty seconds to 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.
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.
- 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).
- 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 ten times its previous volume. The removal of this water vapor from the chamber is vitally important, making the condenser the most critical and expensive component in a freeze-drying plant.
- The freeze-dried granules are removed from the chamber and packaged.
Spray drying is preferred to freeze drying in some cases because of its economy, shorter drying times, 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.
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.
The caffeine content of instant coffee is generally less than that of brewed coffee. One study comparing various home-prepared samples came to the result that regular instant coffee (not decaffeinated) has a median caffeine content of 66 mg per cup (range 29–117 mg per cup), with a median cup size of 225 ml (range 170-285 ml) and a caffeine concentration of 328 µg/ml (range 102-559 µg/ml). In comparison, drip or filter coffee was estimated to have a median caffeine content of 112 mg, with a median concentration of 621 µg/ml for the same cup size.
Regarding antioxidants, the polyphenol content of a 180 ml cup of instant coffee has been estimated to be approximately 320 mg, compared to approximately 400 mg in a cup of brewed coffee of the same size.
Instant coffee appears to be as efficient as regular drip brew coffee in decreasing the risk of diabetes type 2. On the other hand, it has been associated with an increased risk of bladder cancer in women when compared to regular coffee, whereas for men both instant and regular coffee have been associated with an increased bladder cancer risk. However, current review research suggests that there is no dose-response relationship between coffee drinking and bladder cancer, and that previous studies may have been confounded by unidentified risks of bladder cancer.
Instant coffee decreases intestinal iron absorption more than drip coffee. One study estimated that, when a cup of instant coffee was ingested with a meal composed of semipurified ingredients, intestinal absorption was reduced from 5.88% to 0.97%, compared to an absorption of 1.64% with drip coffee. It was also estimated that, when the strength of the instant coffee was doubled, intestinal iron absorption fell to 0.53%. Apparently, however, there is no decrease in iron absorption when instant coffee is consumed 1 hour before a meal, but the same degree of inhibition as with simultaneous ingestion occurs when instant coffee is taken 1 hour after a meal.
Animal experiments have indicated that instant coffee confers no risk related to reproduction, lactation, embryotoxicity or teratogenicity, but possibly a risk of a delay in bone calcification in high doses.
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)
Instant coffee is one of the ingredients in "Caffenol-C", a home-made, non-toxic black-and-white photographic developer. The other ingredients in the basic formula are ascorbic acid and anhydrous sodium carbonate; some recipes also include potassium bromide as a fog-reducing agent. The active ingredient appears to be caffeic acid. Initial experiments on Caffenol were performed in 1995 at the Rochester Institute of Technology; addition of ascorbic acid began around 2000, yielding the improved Caffenol-C, which is less likely to stain negatives than the original formulation. Experiments have shown that cheaper, less desirable brands of coffee work better for this application than more expensive brands.
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- Comparison of different Caffenol formulas
- A Use for that Last Cup of Coffee: Film and Paper Development Darkroom and Creative Camera Techniques, September/October 1995
- One recipe for Caffenol-C
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