Instant tea
When marketed, other ingredients can be added, such as sugar for taste, citric acid for tartness,[2] and other flavors that would not normally be found in tea leaves, such as those of raspberry or lemon.
Physically speaking, the reconstituted tea is mostly water with compounds dissolved within it to give a certain taste.
Flavor and color compounds being evenly distributed when water is added indicates that the reconstituted tea is a homogeneous mixture.
Because of certain legal restrictions in tea producing countries, it is most cost effective for manufacturers to use fermented, undried black leaves, as they do not have to pass through public auctions and are therefore cheaper.
[1]: 538 Quality is not sacrificed, as research has been done to show that this type of leaf has similar flavor when compared to dried, black leaves.
[1]: 539 Research has shown that tea leaf solubles in a column extractor can be described in a system of three components, each which obey a first-order solution law.
The slowest soluble compounds are expected to have either high molecular mass, which would take longer to move through the cell matrices of the leaves, or products formed during hydrolysis over the course of the extraction.
[6] The stripping gas, typically steam, nitrogen, or carbon dioxide, passes through the liquid solution and dissolves the aromatic compounds within it.
Maximizing the surface area for mass transfer is done by using the smallest bubbles possible when stripping.
Research has shown that the cream is a colloidal substance that contains many of the compounds that contribute to color and flavor of black tea, and can contain up to 30% of the total solids.
[8] The driving force behind cream formation is the insolubility of theaflavin and polyphenols, which associate together through galloyl group interactions.
[9] The theaflavins have acidic properties which cause them to have a negative charge at the pH of black tea, which is roughly 4.9.
In the American market, instant tea is expected by the consumer to be clear when reconstituted, which makes the cream an unacceptable part of the solution.
Industrially, a variety of methods have been patented to deal with the issue, such as the utilization of tannase to solubilize the cream.
[11] This process removes the high molecular weight compounds through ultrafiltration, absorption chromatography or oil filtration.
Drying at this point would take too much capital for little gain, and any type of spray or freeze-drying would cause the resulting powder to have too low a density.
Forced evaporation systems had hot spots which led to undesirable sensory characteristics such as stewed and burnt flavors.
Plate heat exchangers can cause the desired evaporation at around 45 °C, with short residence times that reduce the risk of thermal damage.
Spray drying is the final step in creating instant tea, disregarding control points and packaging.
The principle behind spray drying is one similar to that of aroma stripping, where smaller particles have a greater surface to area ratio.
