Instant coffee

Instant coffee in a glass jar

Instant coffee is available in powder or granulated form contained in glass and plastic jars, sachets, or tins. The user controls the strength of the resulting product by adding less or more powder or granules to the water.

Instant coffee is also convenient for preparing iced coffee like the Greek frappé.

In some countries, such as Portugal, Spain, and India, instant coffee is commonly mixed with hot milk instead of boiling water.[9] In other countries, such as South Korea, instant coffee commonly comes pre-mixed with non-dairy creamer and sugar and is called "coffee mix".[10] Said to have been popularised in the UK by GIs during World War II, instant coffee still accounts for over 75 percent of coffee bought to drink in British homes, as opposed to well under 10 percent in the U.S. and France and one percent in Italy.[11]

In the United Kingdom, instant coffee granules are sometimes used to enhance the flavour of sauces used in preparing spaghetti Bolognese.[12][13]

Instant coffee is one of the ingredients in Caffenol,[14] a home-made, non-toxic black-and-white photographic developer. The other ingredients in the basic formula are ascorbic acid (vitamin C) 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;[15] 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.[16]

To produce instant coffee, the soluble and volatile contents of the beans, which provide the coffee aroma and flavor, have to be extracted. This is done using water. Pressurized water heated to around 175 °C (347 °F) is used for this process. The coffee concentration in the liquid is then increased by either evaporation or by freeze concentration.[17][18]

A 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 more expensive, it generally results in a higher-quality product.

1. The coffee extract is rapidly frozen and is broken into small granules. (Slower freezing would lead to larger ice crystals and a porous product; it can also affect the colour of the coffee granules).
2. The granules are sifted and sorted on size.[17]
3. Frozen coffee granules are placed in the drying chamber, often on metal trays.
4. 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.
5. 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.
6. Sublimation—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.
7. The freeze-dried granules are removed from the chamber and packaged.

Laboratory-scale spray dryer.
A=Solution or suspension to be dried in, B=Atomization gas in, 1= Drying gas in, 2=Heating of drying gas, 3=Spraying of solution or suspension, 4=Drying chamber, 5=Part between drying chamber and cyclone, 6=Cyclone, 7=Drying gas is taken away, 8=Collection vessel of product, arrows mean that this is co-current lab-spraydryer

Spray drying is preferred to freeze-drying in some cases because it allows larger scale economic production, shorter drying times, and because it produces fine rounded particles.

The process produces spherical particles about 300 micrometres (0.012 in) in size with a density of 0.22 g/cm³.[19] 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 6,000 pounds (2,700 kg) of solution per hour.[20] 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 (518 °F) OUT = 110 °C (230 °F)

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 main byproduct of the instant coffee production process is spent coffee grounds. These grounds can be used as biomass, for example to produce heat used in the manufacturing process.[21] Roughly two times the mass in spent coffee grounds is generated for each quantity of soluble coffee.[22]