Teas, Herbal Teas, and Coffee

Teas, Herbal Teas, and Coffee Martin JM Michels CHAPTER CONTENTS 36.1 Introduction 36.2 Tea 36.2.1 Composition 36.2.2 Initial microflora 36.2.3 Effect of processing 36.2.4 Spoilage associations and pathogen hazards 36.2.5 Antimicrobial activity 36.2.6 Preservation 36.3 Herbal Teas 36.3.1 Composition 36.3.2 Initial microflora 36.3.3 Effect of processing 36.3.4 Spoilage associations and pathogen hazards 36.3.5 Preservation 36.4 Coffee 36.4.1 Composition 36.4.2 Effect of processing 36.4.3 Spoilage associations and pathogen hazards 36.4.4 Preservation 36.5 Concluding remarks References 36.1 INTRODUCTION The products in this chapter have in common that they are prepared with boiling water and consumed as a drink They are products of long standing of which tea appears to be the oldest, with a history of 2,000 years.93 In the Western world, tea and coffee drinking became a habit about 300 years ago but herbal infusions have been used as a beverage and for medicinal purposes since the Middle Ages The world annual production of tea is million tons and that of coffee nearly million tons; herbal teas form only a small fraction of the coffee and tea market 36.2 TEA 36.2.1 Composition Tea is produced in the tropical and subtropical regions of the world from the tea plant Camellia sinensis* The plant is grown as a bush at high elevations (typically 500-2,000 m); the young top leaves of the bush are plucked and used for making black or green tea The basic difference between these teas is the way the leaves are processed Green tea is unfermented and the leaves are "fired" directly after picking to inactivate the leaf enzymes that would otherwise initiate oxidative fermentation Black tea is made by initiating an enzymic oxidative fermentation process between picking and "firing." The fermentation of the leaf is caused by enzymes released from the tea after withering (moisture loss) and maceration Enzyme activity is stopped by the drying process ("firing") thereafter A third type of tea (oolong) is a semifermented tea that is allowed to ferment for a short period only Black tea forms ca 75% of the total volume of tea produced with ca 25% being green tea Much of the green tea is consumed in China and Japan and is not exported Black tea is defined according to International Standards Organization (ISO) 3720 as "Tea derived solely and exclusively, and produced by acceptable processes, notably fermentation and drying, from leaves, buds and tender stems of varieties of the species Camellia sinensis (Linneaus) O Kuntze, known to be suitable for making tea for consumption as a beverage."42 According to this standard, tea must have no taint and must be reasonably free from ex- traneous matter Other chemical requirements are set to prevent the adulteration of tea with minerals, the sale of spent leaf, and to ensure the adoption of good plucking and sorting standards (a minimum of 32% water-extractable solids, a maximum of 16.5% crude fiber, a maximum of 1% acid-insoluble ash, and a total ash requirement of 4% to 8%) The moisture content, which may be determined by drying at 1030C, is not specified in the ISO standard, although it is the low moisture of the final product that ensures the long storage life of tea In practice, the moisture content of high-grown black tea may range from 3% to 4% directly after drying, to about 7% to 8% after shipment to the tea packing plant Lowgrown tea (cultivated below 500 m altitude) is exposed to more humid conditions than tea grown at higher altitude and may have moisture levels close to 10% (see Section 36.2.3) For green, artisanal tea this may be above 10% The main characterizing components of tea are its polyphenols, often incorrectly referred to as tannins The main polyphenols of green tea (the colorless catechins) are converted during the fermentation step of black tea production into the red-brown theaflavins and thearubigins The polyphenols of black tea constitute 10% to 20% of its dry weight, and ca 30% of the solids extracted during brewing of the tea to prepare as a beverage The other important characterizing component of tea is caffeine, which constitutes 1.5% to 5% of its dry weight and 5% to 8% of the solids extracted during brewing 36.2.2 Initial Microflora Little has been reported about the microbial load of fresh tea leaves Analysis of fresh leaves of the Yabutika cultivar, commonly used for green tea production in Japan, established a mold and yeast count of 7,500 g-1 of which ca 2,500 g-1 was tentatively identified as Cladosporium cladosporoides.15 Fresh leaves from gardens near Bangalore (India) were analyzed (after frozen storage) on three separate occasions (in March, May, and July) The counts obtained varied from 14,000 g-1 (May) to 193,000 g-1 (July), with an intermediate count of 82,000 g-1 in March Mold counts ranged from 45 g"1 in July to 600 g-1 in March Yeasts were not detected (