The Harney & Sons Guide to Tea - Michael Harney [55]
ROLLING
After green teas have been fixed, and before black teas darken, tea makers roll the leaves to give them their lovely shapes. Once done by hand but now performed mainly by machine, rolling transforms the flat leaves into mesmerizing twists, coils, balls, or spears. In general, lightly rolled teas have mellower and gentler flavors, while leaves rolled with greater pressure break up into smaller pieces and form brews that are more brisk and intense. Chinese tea makers have invented innumerable balletlike hand movements over the centuries to create dozens of leaf shapes. In the 1880s, the British developed rolling machines that saved labor but made far less distinctive shapes and less refined teas.
OXIDATION
Where rolling gives green tea leaves their lovely shapes, with oolongs and black teas it also provokes the reaction that darkens the leaves. Oolongs and black teas are not fixed green but are allowed to darken through a process called “oxidation.” In the tea world, for centuries this process was mistakenly called “fermentation,” on the assumption that yeasts or bacteria were involved. In fact, the reaction involves only polyphenols and oxygen.
In a healthy tea leaf, polyphenols reside in “vacuoles,” small chambers inside the plant cells, ready to defend the leaf against damage from insects and other hazards. If insects munch on the cells, or strong winds bruise the leaves as they rub against one another, or a tea maker macerates a leaf during the rolling process, the vacuoles also break, releasing the polyphenols into the cells’ cytoplasm. In the cytoplasm, the polyphenols encounter the enzyme polyphenol oxidase, or PPO. In green teas, this enzyme does nothing, as it gets deactivated when the leaves are fixed—heated to 160 degrees Fahrenheit to render the enzyme inoperable. In oolongs and black teas, however, PPO reacts with the polyphenols and oxygen to form brown-colored compounds. In nature, these polyphenols are thought to deter further attack by giving the insects a stomachache. Luckily for tea drinkers, polyphenols are delicious as well as lovely to behold. In tea, there are two principal types of polyphenols, each with its own flavor and color. Golden, brisk theaflavins are the first to emerge. Later, thearubigins develop, mellower and with a lovely copper hue. The slower the oxidation, the more thearubigins, the gentler the teas.
Oolongs oxidize more slowly than other teas. As a result, they have the most complex, mellow flavors. Oolongs start to oxidize when they wither, because tea makers gently fluff the leaves on tarps in the sun. This fluffing qualifies as a very light rolling, triggering oxidation along the edges of the leaves. Indeed, the gentle agitation is what gives oolong leaves their characteristic red tinge. With a head start on oxidation, the edges turn a darker red than the rest of the leaf. After withering, the leaves are rolled incrementally, in an elaborate stop-and-start oxidation that lasts for six hours or more. This gradual oxidation prolongs the withering, allowing for the creation of yet more aromatic compounds. The final flavors and aromas depend entirely on the amount of time the oolongs are given to wither and oxidize. Of the nine oolongs in this book, the first four oxidize only roughly 25 percent. They contain high concentrations of linalool, methyl jasmonate, and indole and thus have the citrus and floral aromas of lime, jasmine, and gardenia. The final five oxidize between 40 and 75 percent and develop more of the apricot and peach flavors typical of carotenoid degradation, the later-stage transformation of the pigment carotene into the apricotlike compounds ionones, damascones, and damascenones.
Chinese black teas share many of these apricot notes. Though they oxidize more quickly than oolongs because of stronger rolling, they still oxidize slowly enough to produce sweet, mellow thearubigin-rich teas. The oxidation