Black fermentation

Phenol has been reported at concentrations of 7 and 28.6 ppm in smoked summer sausage and smoked pork belly, respectively (EPA 1980), and was identified but not quantified in mountain cheese (Dumont and Adda 1978), fried bacon (Ho et al. 1983), fried chicken (Tang et al. 1983), and black fermented tea (Kaiser 1967). Phenol has also been found in honey at concentrations ranging from 0 (detection limit 0.1 ppm) to 19 ppm (Spoms 1981). It was present each time the honey was collected with phenol-treated boards. 

C7H6O5. Colourless crystals with one molecule of water, m.p. 253" C, sparingly soluble in water and alcohol. It occurs free in woody tissue, in gall-nuts and in tea, and is a constituent of the tannins, from which it can be obtained by fermentation or by acid hydrolysis. It gives a blue-black colour with Fe and is used in the manufacture 6f inks. On heating it gives pyrogallol. 

When ground and mixed with water, the seeds of black mustard ferment and yield a sharp, irritating odor and a pungent taste white mustard does not react in this manner. 

Pepper, White. This spice is derived from the same plant as black pepper except that the berries are allowed to ripen fully. The dark outer hulls are removed by mbbing and washing after soaking and fermentation. White pepper has generally the same flavor and aroma as black pepper however, it is milder and has a slight fecal odor. 

Alcohol dehydrogenase (5) and leucine a-ketoglutarate transaminase (33,34) contribute to the development of aroma during black tea manufacturing. Polyphenol oxidase and peroxidase are essential to the formation of polyphenols unique to fermented teas. 

FIa.VOnoIOxida.tlon, The fermentation process is initiated by the oxidation of catechins (1) to reactive catechin quinones (13), a process catalyzed by the enzyme polyphenol oxidase (PPO) (56). Whereas the gaHocatechins, epigaHocatechin, and epigaHocatechin gaHate, are preferred, polyphenol oxidase can use any catechin (Table 2) as a substrate. This reaction is energy-dependent and is the basis of the series of reactions between flavanoids that form the complex polyphenoHc constituents found in black and oolong teas. 

BlackTea. The black tea manufacturing process has evolved over hundreds of years, until the early part of the twentieth century, Httie was known about the chemical changes. The process consists of the unit operations of withering, rolling, fermentation, firing, and sorting (4). 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

Process Va.ria.tlons. The conventional techniques for tea manufacture have been replaced in part by newer processing methods adopted for a greater degree of automation and control. These newer methods include withering modification (78), different types of maceration equipment (79), closed systems for fermentation (80), and fluid-bed dryers (81). A thermal process has been described which utilizes decreased time periods for enzymatic reactions but depends on heat treatment at 50—65°C to develop black tea character (82). It is claimed that tannin—protein complex formation is decreased and, therefore, greater tannin extractabiUty is achieved. Tea value is beheved to be increased through use of this process. 

Stout. Stout is a very dark beer with a sweet, slightly burned taste and a strong malt flavor. It is heavier than porter and is strongly, hopped. It contains 6.3—8.3% by vol alcohol. Storage time is about six months and fermentation usually occurs in the bottie. Dry and sweet stouts ate brewed using different amounts of black malt, caramel malt, and hops (6). 

J. Black showed that CO2 was produced by fermentation of vegetables, by burning charcoal and by animals (humans) when breathing turns lime water turbid,... 

Turker, N. et al., Effect of storage temperature on the stability of anthocyanins of a fermented black carrot Daucus carota var. L.) beverage shalgam, J. Agric. Food Chem., 52, 3807, 2004. 

Tea oxidation is generally referred to as fermentation because of the erroneous early conception of black tea production as a microbial process.66 Not until 1901 was there recognition of the process as one dependent on an enzymically catalyzed oxidation.67 This step and further reactions result in the conversion of the colorless flavanols to a complex mixture of orange-yellow to red-brown substances and an increase in the amount and variety of volatile compounds. Extract of oxidized leaf is amber-colored and less astringent than the light yellow-green extract of fresh leaf and the flavor profile is considerably more complex. 

Black tea quality as determined by theaflavin levels is also affected by storage conditions. Low temperatures, low moisture levels, and low oxygen availability retard theaflavin loss. Residual peroxidase activity, which accelerates theaflavin loss on storage, is diminished by acid treatment during fermentation.94... 

The sensitivity of tea production to research has already been demonstrated by the successful process modifications carried out to increase theaflavin levels and value. There is a limit to what can be accomplished to the confining environment of fermenting leaf. For black instant tea production, the conversion of fresh leaf components to those present in black tea might be better accomplished outside of the leaf. This could allow for more highly directed reaction pathways to bring about the formation of the most desirable end-products. Enzymic and chemical techniques could also be used. 

Sanderson, G. W., Biochemistry of tea fermentation Conversion of aminoa cids to black tea aroma constituents. J. Food Sci., 35 160, 1970. 

Cloughley, J. B., The effect of fermentation temperature on the quality parameters and price evaluation of Central African black teas. J. Sci. Food Agri., 31 911, 1980. 

Asamoa and Wurziger tabulated the caffeine content of a variety of cocoa beans.22 The mean concentration (percentage in fat-free samples) in Amelonado and Amazonas beans, respectively, after 5 d of fermentation at various stages of maturity were green beans 0.06,0.19 yellow 0.09,0.18 orange 0.08, 0.23 and black 0.10, 0.22. These results confirmed significant differences between the two varieties and also the low caffeine content of Forastero-type beans. The caffeine content of 16 other samples of various... 

Quinone may be prepared by the oxidation of aniline with dichromate or manganese dioxide and sulfuric acid.1 This is a more feasible commercial method than the one given. However, the oxidation of hydroquinone is more rapid and convenient and, hence is more desirable for use in the laboratory. Various materials have been oxidized by chemical means to give quinone they are quinic acid,2 hydroquinone,3 benzidine,4 -phenylene-diamine,5 sulfanilic acid,6 / -phenolsulfonic acid,7 arbutin,8 aniline black,9 and the leaves of various plants.10 Quinone is also formed by several other methods by the fermentation of fresh grass 11 by the action of iodine on the lead salt of hydroquin-... 

---