Issue Date: September 29, 2008
COFFEE IS ONE of the world's favorite beverages. It is definitely my liquid of choice, with all the invigorating caffeine, great taste, and wonderful-smelling volatile compounds such as 4-(4-hydroxyphenyl)-2-butanone, which gives coffee a sweet, fruity aroma. Organic, fair-trade whole-bean coffee is my preference, but those with less patience may desire long-lasting, easy-to-prepare "instant" soluble formulations.
The Japanese were the first to produce a stable instant coffee product in the early 1900s. During World War II, instant coffee gained fame among American soldiers after Nestlé marketed its Nescafé brand.
The instant beverage was updated in 1963, when Kraft introduced its Maxwell House freeze-dried instant coffee, which the company claimed tastes more similar to fresh-brewed coffee than other instant coffee products. Within a few years, all major manufacturers had freeze-dried coffee products on the market.
Taste and smell aside, most people drink coffee in all of its incarnations for that energizing alkaloid compound, caffeine. According to the National Nutrient Database for Standard Reference, instant coffee has about two-thirds the caffeine content of fresh-brewed coffee. More precisely, 8 oz of freshly brewed coffee contains 95 mg of caffeine, whereas the same amount of instant coffee has only 62 mg of caffeine.
But the caffeine content of coffee depends on many factors, including coffee bean species, bean ripeness, and the roasting and brewing processes. Thus, citations of caffeine content in different coffee beverages are reported with exceedingly wide ranges, and the database figures are more a rule of thumb than law.
All instant coffee production involves roasting coffee beans and then brewing them in hot water. Before the brew can be further processed into instant coffee, oxygen and insoluble particles such as coffee grounds must be removed. After this, the brew is dried by one of two methods to yield instant coffee.
One common way to desiccate the brew is through spray-drying: The coffee is sprayed through a nozzle to produce tiny 300-µm-sized droplets that fall through drying towers until they reach the base as a parched powder. The drying towers are kept at high pressures and temperatures near 270 ºC. The fine coffee powder may be rewetted to produce larger granules that are dried and finally packaged.
In the freeze-drying process, the brewed coffee is first frozen and then crushed to obtain the desired granule size. Standard & Alternative Products (SAAP), which produces instant coffee products, aims for granules of about 3 mm in diameter, for example. Granules that are too large or small are melted and refrozen. Frozen granules of the proper size are placed in low-pressure drying chambers at –50 ºC, and the water is removed by sublimation as the drying chamber warms.
Both processes run the risk of losing compounds that contribute to the desirability of the drink. For instance, caffeine sublimates at 180 °C at atmospheric pressure, so the high temperatures in spray-drying chambers may affect instant coffee's caffeine content and the content of organic compounds that provide taste and aroma. Whichever process is used, the final product is often packaged under carbon dioxide or nitrogen because the presence of oxygen will cause further loss of aroma and flavor.
ALL THIS PROCESSING means instant coffee contains little oxygen and has a water content of only 1 to 4%, much lower than microbes need to grow, allowing the product to stay on the shelf for more than two years without spoiling.
Today, most major manufacturers still use a freeze-drying process to make their instant coffees, says Daniel Gedance, president of SAAP. Although instant coffee is generally viewed as inferior to fresh coffee, Juliet Morris, sales manager of Just Us! Coffee Roasters Co-op, chooses to stock freeze-dried instant coffee because the freeze-drying process "most closely allows the fresh-roasted flavor of coffee to come through," she says.
But some instant coffee manufacturers do not use the freeze-drying process because of its prohibitive costs, Gedance says. Although the price of any retail instant coffee is determined largely by costs related to distribution, freeze-dried instant coffee production costs are 35% higher than the costs of production by spray-drying, he notes. The freeze-drying process is more expensive because making the same amount of instant coffee by freeze-drying methods requires larger quantities of better-quality beans than does the spray-drying process.
Susan C. Jackels, a chemistry professor and coffee researcher at Seattle University, says that beans used for some instant coffee products could not be sold for use in roasted, ground coffee products. For some instant coffees, however, coffee "cherries" are stripped from plants at the end of the season, whether they are ripe or not. Unripe beans add a bitter taste to coffees and have a less-well-developed aroma.
For people on the go, instant coffee might be the best thing since sliced bread. I, however, will stick to grinding my own beans.
- Chemical & Engineering News
- ISSN 0009-2347
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