Australia's Secret ? Enological Tannins

Australia's secret ? : Enological tannins

June 09, 2003     Volume X Number 6         NY Wine Industry Workshop   Australia's Red Secret and MLF Discussed   By David Falchek   Attendees at the 32nd Annual New York Wine Industry Workshop in Geneva, New York braved a late-season ice storm in April to discuss topics of warmer times: winemaking. Sponsored by the Cornell Wine Research and Extension Program and the New York Wine & Grape Foundation, the three-day event drew over 300 participants from across the continent and speakers from around the globe. The program included uses for enzymes and oenological tannins, new methods for malolactic fermentation, and a discussion of what could be the next big regulation--limiting the amount of histamine permitted in wine. Australia's Secret? The secret behind the ability of Australian reds to so quickly claim a place in the international market is oenological tannins, said Scott Lab's Diane Burnett. Scott's representative to Australia sells heaping truckloads of tannin Down Under, Burnett said. Bordeaux winemakers use oenological tannins, though don't admit it. Yet US winemakers are slow to embrace the easy, and easily reversible, process, Burnett noted. "The reason Australian reds are so approachable and drinkable sooner, is because of the tannins," she said. More winemakers in hot, high-sugar growing regions where grapes rarely achieve phenolic maturity--such as Texas, Colarado and the Central Valley--are adopting the mantra "harvest early, add tannins." Although tannins may seem costly when using it by the pound, Burnett said the cost for small producers is between three and seven cents per case. Beringer Blass Wine Estates senior research enologist Tom Collins discussed tannin's conventional role of color stability and wine quality. Christophe Gerland, a consultant withItell'oeno, in France followed with new roles for tannins--from preventing oxidation to promoting riddling. When one sees the rich purple juice coming from the crusher destemmer, it's natural to wonder at bottling, or a year or two later, where all that color went. That color comes from Anthocyanin compounds. A fickle bunch not cut out for the excitement of fermentation or the boredom of the bottle, anthocyanins prefer to just drop out. The key to keeping anthocyanins at the party is to get them to hook up--with tannins. Unfortunately, this polymerization doesn't always happen, or happen enough, in red fermentations. Anthocyanins are in grape skin. Water soluble, they are easily liberated into the must, as one can see during crush. The first few days, they are everywhere. Tannins arrive at the fermentation ball later, extracted in significant numbers after two or three days. But by then, most anthocyanins have precipitated away like Cinderella at midnight. With oenological tannins, winemakers can become matchmaker, getting tannins and anthocyanins in the same place at the same time. Collins found the best way to do that is to add enological tannin before, during and after fermentation in multiple, small doses. He applies between 50 and 75 ppm several times over the course of three days for a total of 100 to 200 ppm. The polymerization that follows provides color stability, adds structure and mouthfeel, and imparts oak qualities. The post-fermentation dose, the one most likely to improve structure and mouthfeel, is tricky, however. To allow for tannin precipitation and polymerization, filtering is best put off for days, or weeks if possible. Gerland said that through the last decade in Europe, research into tannin additions and use in the cellars has dramatically increased and found applications in white and sparkling wine. Winemakers have assembled tannin sources beyond grapes and oak and found a range of benefits that make them sound almost like huckster's cure-all. Grape tannins are expensive. Less costly tannin sources from exotic woods or nuts are in some cases more effective than grape tannins. In whites, tannins help prevent oxidation. Gallic tannin derived from soybeans prevents oxidation in grapes that are botryitisized or that have a low polyphenol content. Tannin additions allow winemakers to safely cut back on SO2 additions. Reduced sulfur compounds can be eliminated by 50 to 100 ppm of the chestnut-derived tara tannin, which works with oxygen to remove sulfur. The chestnut tannins when added at 100 ppm aids fining by promoting the flocculation of gelatins. Oak tannins enhance the structure of whites, offering slightly wooden aromas at applications from 20 to 100 ppm. But Gerland sees a range of results from different commercial oak tannin preparations and urged careful blind bench trials. Three tannins may be employed in sparking wine production with 50 ppm of chestnut tannins at the end of malo-lactic fermentation to improve structure and riddling for later triage. Then a combination of chestnut and oak tannins at 30 to 50 ppm is added with the dosage. At disgorging, 30 to 50 ppm of oak tannins adds mouthfeel and aroma. In red must, tannins help augment the tannins in low maturity grapes while allowing the winemaker to reduce maceration time, which in the case of unripe grapes can extract nasty green tannins. Quebracho tannin, derived from the tree in Central and South America, provides structure and stabilization at rates of 100 to 400 ppm. Ellagic tannins are able to protect color during aging and prevents oxidation. A combination of quebracho and ellagic tannins added in two doses--on the must and after fermentation--give better color and taste. Maceration's Exclamation Enzymes are maceration's exclamation point. Whatever is in the fruit will be drawn out by enzymes, stressed Widmer Wine Cellars winemaker Glenn Curtiss and Gerland in their respective talks. Curtiss is winemaker at Widmer in Naples, NY, a long-standing piece of Constellation Brands' now-global empire. There, Curtiss makes a combination of bulk and small batch "boutique" wines. He's found enzymes useful in increasing quantity and quality for all styles. Commercial enzymes, typically a mixture of several enzymes, are most commonly used as pectinase to break down grape cells and increase juice yield and filterability. Curtiss found enzymes increase the volume of his labrusca crush up to 5 percent. Vinifera crush increased two to three percent. Beyond gallons, the act of dissolving the cells of the grape wall extracts anthocyanin and tannins to increase color and structure. Some enzyme preparations can have other beneficial side effects, Curtiss said. In wines such as Riesling, Viognier, and Gewürztraminer, beta-glucosidase frees aromatic compounds called terpenols from sugars so they can be perceived by the senses. While he sees a brand difference in some enzymes--particularly those that claim side activities--he said winemakers who want them solely for depectinization may purchase based only on price. Bench trials are a must. For example, Curtiss' Pinot Noir comparisons showed that half the 30 gram per ton standard dose of EVG extracted more color and was twice as likely to be the preferred by a tasting panel. Gerland discussed how white grape cold soak has been combined with enzymes to obtain more full-bodied and aromatic wines. Echoing Curtiss, Gerland found extraction enzymes, between 2 and 4 grams per 100 kilograms soaked for six hours, not only increases juice volume, but also the aroma and roundness of the wine. Enzyme protocol, however, is changing. Instead of adding aromatic enzymes at the end of fermentation, more European winemakers add them at the front end, before cold soak. They have learned that beta-gludosidase enzymes, mixed with macerating enzymes and added at cold soak, yield greater aromatic intensity, reveal norisopreniods, and increase overall wine quality. Gerland said the two enzymes appear to work in synergy. Muscat, Gewüztraminer, and Riesling clearly benefit, however, low-aromatic grapes such as Chardonnay, Ugni Blanc, and Muscadet also improve. Enzymes are hardly a magic bullet, both speakers noted. Used improperly, they can backfire. Grape maturity is critical for enzyme use in reds, Gerland stressed, with several French studies showing that extraction of tannins and anthocyanins, fruity aromas, and color are greater in optimally ripe grapes. In grapes that aren't mature, enzymes increase stringency and vegetal aromas. Gerland also cautioned the audience to avoid enzymes containing cinnamoyl-esterase activities particularly for long-aging reds or barrels-destined wines where Brettanomyces risk is high. Enzymes that bill themselves as "purified" tend to be free of cinnamoyl-esterase. A New MLF Of all the processes of winemaking, one of the least understood is malolactic fermentation. In some cases, even by-the-book winemaking results in failed MLF. One explanation, said Sibylle Kriegerof Lallemand Inc., is a combination of substances in wine that inhibit ML such as SO2, alcohol and pH. Several experiments by Thomas Henick-Kling, enologist at Cornell, show that a simultaneous inoculation with yeast and ML culture can help guarantee the completion of ML before the accumulation of inhibitory substances, Krieger said. The type of yeast used is critical. Yeast known as big SO2 producers and nitrogen consumers shouldn't be used in any must meant to undergo any MLF. The K1 yeast strain is a prodigious SO2producer while 71B and Wädenswil produce much less and are most favorable for MLF. Musts hosting a yeast that is both nitrogen-hungry and SO2-producing is almost unable to undergo any MLF. Adding ML starter culture with yeast inoculation seems to violate an old winemaker rule--MLF in the presence of sugar will yield acetic acid. However, Krieger said other research has shown that excessive acetic acid will not be produced so long as yeast fermentation is strong, healthy, and goes to completion. The greater concern is that MLF will inhibit yeast fermentation. Initially, the yeast and ML bacteria both compete for the available nutrients in the must. The ML bacteria sustain themselves as the yeast flourish for the first ten to 20 days of fermentation. The dying yeast cells return nutrients to the must and the ML bacteria dominate. The Next Reg? No one knows for sure why, but a greater number of people are having adverse reactions to histamines, a ringleader in a group of substances known as biogenic amines that occur in many foods. Jurg Gafner has studied the issue at the Federal Research Station in Wädenswil, Switzerland, where a law limits biogenic amines in wine to no more than 10 ml/l. France, Belgium and Germany either have laws on the books or in the works limiting biogenic amines in wine to lower levels. "This is not a topic in the US yet, but you need to be one step ahead of regulators," Gafner said. "Biogenic Amines could be an export barrier in the future." Biogenic amines result from the decomposition of protein and are common and expected in aged cheeses and sausages. Regulators already use biogenic amines to determine the freshness of fish. People with histamine intolerance react drastically after consuming histamines, with itching, headache, nausea and difficulty breathing. While many foods have histamines, alcohol consumption reduces the body's ability to degrade histamine. Gafner said biogenic amines don't belong in wine. They are a by-product of spoilage microorganisms. Sanitary winemaking practices are the best way to keep them at a minimum. Amines are closely linked the activity of the bacteria Pedicoccus damnosus and Brettanomyces. A vigorous, continuous alcoholic fermentation with a commercial yeast, and inoculation with an ML starter culture that does not form amines will reduce total amines in wine. wbm David Falchek  , based in Pennsylvania, covers the East Coast wine scene for the Finger Lakes Times, and others. He is available via his email address [email protected] .