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68 WINES&VINES February 2018 GRAPEGROWING noble rot induces the biosynthesis of anthocyanins, complex flavo- noids whose development is nor- mally limited to red-skinned grapes," Cantu says. The pigment that Cantu de- tected in the laboratory reflects the change in pigmentation "We've confirmed the impor- tance of these metabolic pathways in infected grapes by measuring the concentration of metabolites and analyzing enzyme activities," Cantu explains. Secondary metabolic pathways triggered by noble rot also gener- ate aromas, flavors and textures that are unique to late-harvest wines. Cantu discovered that in- fected Sémillon cells express higher concentrations of several other phenolic compounds. "Acetophenones and phenolic glycosides showed an increased abundance at all stages of the infection," he explains. Antioxi- dants and antimicrobials first, they help shape the sensory pro- file of the grapes and the wine. Terpenes can also influence aroma. "Monoterpenes, triter- penes, sesquiterpènes and ter- pene glycosides accumulate at all stages of noble rot," Cantu says. "Fatty acid aroma precur- sors also increase as the infec- tion progresses." Glycerol, mannitol and sorbitol concentrations increased signifi- cantly in infected berries along with free galacturonic acid, arabi- nose, galactose, rhamnose, man- nose and xylose. "We profiled metabolites (for the aromas and flavors) of late- harvest wines produced from the John's Creek vineyard and cor- roborated that key compounds from noble rot carried over to the wines," Cantu says. Earthy to elegant At the winery, the crew weighs the fruit and loads it into the press. The immediate goal, according to Allen, is to prevent "a microbial zoo" from spoiling the fruit. He separates two-thirds of the juice into small batches and in- oculates each with one of five strains of commercially available yeast. Weak fermenters, they are well suited to the high osmotic pressures of concentrated juice. Wild yeasts ferment the rest of the vintage. "Every batch of juice ends in a stuck fermentation," he says, recalling a viticultural and micro- bial mix that defies conventional wisdom. "The juice contains so much glucose, fructose and etha- nol that the yeast die or go dor- mant before it can convert all of the sugar to alcohol." Some winemakers—most no- tably vignerons from the Alsace region of France, vinify late-har- vest wines toward dryness. The yeasts convert much of the sugar to alcohol. Allen strives to balance residual sweetness with acidity. While yeast affects the bal- ance between ethanol and acid, the aromas, color, flavors and textures of Dolce late-harvest wine are the work of a medley of microorganisms. Yeast, together with other fungi, mold and bac- teria, produce flavors and aro- m a s , c o m b i n e m o l e c u l e s t o enhance texture and rely on en- RED BLOTCH IS HARDLY NOBLE W hile Botrytis cinerea or noble rot accelerates the devel- opment of grapes beyond what's merely ripe, red blotch turns back the clock shortly after véraison. "We determined that red blotch-infected berries induced metabolic pathways that are normally associated with early fruit development," says Dario Cantu of UC Davis. His research demonstrates that noble rot, a mold, induces metabolic pathways that hasten the development of aroma, color and flavor. Red blotch, a virus, blocks or delays those same pathways, triggering metabolic processes more com- mon to the early stages of ripening. mm