page_title: Instant tea
section_title: Manufacturing
hierarchical_section_title: Instant tea / Manufacturing
caption_attribution_description: English: instant tea
context_page_description: Instant tea is a powder in which water is added, in order to reconstitute it into a cup of tea. The earliest form of instant tea was developed in the United Kingdom in 1885. A patent was granted for a paste made of concentrated tea extract, sugar, and evaporated milk, which became tea when hot water was added. However, no notable developments were made until spray drying technology allowed for drying the tea concentrates at a temperature which did not damage the flavors of the product.
context_section_description: Production of instant tea can be broken down into six main steps: selection of raw materials, extraction, aroma stripping, tea cream processing, concentration, and drying.
  Selection of tea leaves is done with the best interests of both the manufacturer and end user.  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.  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.
  Extraction is done with two goals in mind: yield of tea solids extracted from the leaf, and concentration of the extract solution.  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 explanation given for why the soluble compounds fall into any of these three categories is based on how accessible they are.  The instantly soluble compounds are likely to be right on the surface of the leaf, which is why they are the first to be obtained.  The rapidly soluble components are thought to be from the inside of the leaves, where broken cell structures slow both the rate of solvent entering as well as solute leaving.  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.  There are a variety of methods and machinery that can be used to perform extraction, but the general concept is that the leaves are treated with a solvent in order to extract the compounds within them.  In the aforementioned study, it was stated that the maximum yield of solids that could be extracted was 35%.  Over time, other chemical methods of increasing extraction yields have been discovered, such as using hydrogen peroxide on extracted leaves to obtain a yield of 42% solids.  After the extraction step, the solution is clarified by passing through a decanter, centrifuge, or filter press.
  Stripping is a physical separation process where components can be removed from a liquid stream through usage of a vapor stream.  The stripping gas, typically steam, nitrogen, or carbon dioxide, passes through the liquid solution and dissolves the aromatic compounds within it.  Aroma compounds are easily volatilized into the air.  For this reason, passing gas through the liquid provides a favorable condition for the compounds to leave the liquid.  The equation for determining rate of mass transfer between a food and the gas phase is:
  dm/dt = 2(Dc/πtc)1/2Agc[cₑⁱ(t) - cₑ(t)] or = hDAgc[cₑⁱ(t) - cₑ(t)]
  Where hD is the overall mass transfer coefficient and is substituted for 2(Dc/πtc)1/2.
  The variable dm/dt is the rate of mass transfer into the gas phase, De is the average diffusion coefficient of free aroma molecules in the emulsion, Agc is the surface area of the gas/food interface, tc is the time that the surface elements are exposed to the surface, and cei(t) and ce(t) are the concentrations of aroma compounds in the interface and emulsion, respectively.
  With respect to stripping, Agc has the greatest effect on the mass transfer rate. Maximizing the surface area for mass transfer is done by using the smallest bubbles possible when stripping.  Assuming spherical structure of the bubbles, the surface area is given by 4πr², and the volume is given by (4πr³)/3. This implies that at any increase in radius, the volume increases by a greater factor than the surface area. This also means that at the smallest possible volume, there will be the greatest surface area to volume ratio, giving a greater surface area for reactions.  The use of inert gas is favored because it prevents oxidation, and therefore deterioration of the aroma compounds.
  Black tea contains compounds that have low solubilities, which tend to bind together. The solution becomes cloudy and changes color to pale br
caption: Various reconstituted instant teas
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