Instant

Instant-tea powder is generally prepared by the aqueous extraction of black tea followed by concentration and drying. It is also possible to prepare instant tea from green tea or from oxidized leaf prior to the drying step. As most tea consumed in the United States is drunk as a cold beverage, the cold-water insolubility of the important cream fraction introduces technological problems in manufacture. A product prepared simply by extraction with hot water, concentration, and drying will not rehydrate completely without applied heat or the use of additives. Cold-water extraction does not recover sufficient solids to meet organoleptic or economic criteria. Most instant-tea technology is concerned with ways to resolve this problem. Tea cream, the fraction that precipitates when a black-tea solution is cooled, constitutes 15 to 30% of the original extract solids. The quantity varies with the type of tea, the extract concentration, and the temperature to which the extract is cooled. Beverage color, caffeine content, and taste are disproportionately concentrated in the cream fraction. Tea cream is a complex of the oxidized polyphenols material with caffeine along with other occluded substances. The aggregates that develop on standing include other components of tea extract, such as proteinaceous material, lipids, and waxes. Freshly precipitated cream can be resolubilized by heating. The first instant teas that appeared on the U.S. market were prepared by discarding the cream after cooling the hot extract. The cream problem was solved in many ways as indicated by a copious patent literature. Most approaches are based on the disruption of the caffeine—tannin complexes.

Manufacture

Tea is extracted with hot water in a countercurrent mode, either batchwise in kettles or in columns. Continuous extraction systems have been described (72). Aroma fractions are collected by vacuum stripping and condensation or by separation and preservation of the first column effluents. They are retained for later addition to the product stream. Vacuum concentration to the desired solids level for adequate cream separation may then be carried out. Prolonged storage of extracts at elevated temperatures is avoided to prevent oxidative and microbiological deterioration. Tea cream is solubilized or avoided by several different procedures. Treatment of cream with the enzyme tannase results in the selective hydrolysis of gallate linkages, thereby increasing solubility (73). Similarly, it is possible to treat black tea with tannase to produce a cold-water-extractable product (74). The addition of unoxidized (green tea) catechins to black-tea extract prevents the formation of insoluble substances by competitive complexa-tion (75).

Several oxidative procedures for the conversion of green-tea extracts to black tea have been described. These include the use of oxygen, ozone, or hydrogen peroxide (7678). The reactions are carried out in an alkaline medium so that oxidation and hydrolysis occur simultaneously. These oxidized green-tea extracts are useful in instant-tea manufacture because color and solubility control are easily effected by their addition to the black-tea extract stream.

If cream has been solubilized apart from the remainder of the extract, the fractions are recombined and the total extract is brought to the concentration desired for drying. Vacuum or freeze concentration may be utilized. Concentration by reverse osmosis has also been described as useful for flavor conservation (79). Retained aroma fractions, often concentrated, are added to the drier feed.

Most instant tea is spray-dried. Pectins extracted from tea or other sources have been used to control final product density (80). Inflation of particles with carbon dioxide during spray-drying controls density and wall thickness. Both parameters affect product solubility. Instant tea may also be freeze-dried. The treatment of spent tea leaf with a /?-gluconase or cellulase to hydrolyze leaf components adds to the yield of extract solids and decreases the disposal load. The additional use of proteases enhances this effect. The extraction of fermented green leaf, omitting the firing stage, is an attractive process for use in tea-growing countries to conserve energy. Minor amounts of instant tea are prepared for hot beverage consumption. Processing is simpler and taste is more authentic.

Product Characteristics

Instant-tea powders are usually manufactured with a density of ca 0.1 g/mL. Products are soluble in cold tap water and produce a clear solution with an authentic tea color and taste. Instant-tea mixes that contain sugar or a non-caloric sweetener and various fruit flavors are widely used. Canned iced tea beverages containing sweeteners and flavors are also based on instant tea. Decaffeinated instant tea has also come into use. Most instant tea is manufactured and consumed in the United States, where it accounts for ca 15% of total tea usage. Production in 1998 was ca 2,5001. Kenya, India, and Sri Lanka together manufacture ca 5,0001, more than half of which is exported to the United States (1).

READY-TO-DRINK (RTD) TEA

RTD teas represent the fastest-growing mode of tea consumption in the United States. In 1997 ca 1 billion L was produced. They are usually presented as a sweetened, flavored, slightly acidified beverage. Taste stability and maintenance of clarity under refrigeration pose major technical problems in their manufacture. The addition of high methoxy pectin to an acidified, flavored tea extract at normal beverage strength (ca 0.3%) results in a clear, cold-water-stable product (81). Gum arabic provides the same benefits (82).

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