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72 WINES&VINES April 2018 WINEMAKING PRACTICAL WINERY & VINEYARD Fortunately, one of the first options in the vinification process for white wine turns out to be one of the most effective: settling and clarifying the juice prior to yeast inoculation. Thoroughly settling and racking the juice be- fore fermentation can reduce MP content by more than half, al- though it should be noted that this particular juice had a high initial level of solids at 1,280 NTU (see "Juice Settling Can Sig- nificantly Reduce Greenness in Wines," left). Thermo-vinification has been shown to be effective at reducing MP content in must. It involves heating red grapes and must for a short period to between 140° and 176° F (typically to aid in phenolic and color extraction), and is used widely in France and Germany. A reduction in IBMP content of up to 67% has been reported using thermo-vinifica- tion, 23 with more modest de- creases found for other MPs. 14 A newer heat treatment, flash- détente, involves heating the grapes for less than one minute to around 185° F and then cool- ing them in a vacuum. A reduc- tion in the herbaceousness of the resulting wine is widely claimed anecdotally; whether this is due to a loss of MPs, other green com- pounds and/or a change in other volatile constituents remains to be determined in the peer-re- viewed literature. Fermentation Low temperature pre-fermenta- tion maceration (cold soaking) to extract color and aromatic com- pounds is not recommended with high-MP grapes. While yet to be widely investigated, there is no evidence that commercial yeast strains can degrade MPs during fermentation. In fact, red wine fermented with the Lalvin BM45 cerevisiae yeast showed increased levels of IPMP, 21 suggesting it should be avoided in musts with high MP levels. Yeast strains may also impact perceived greenness in wine in- directly, particularly through sup- p r e s s i o n a n d e n h a n c e m e n t effects. For example, Cabernet Sauvignon wine fermented with Lalvin D2 produced wines that were less green in aroma and flavor than those fermented with three other commercial Saccha- romyces cerevisiae strains (see "Green Characters in Red Wine are Affected by Yeast Strain" on this page), demonstrating the capacity for vintners to mask green characters to some degree by selecting yeast that produce high levels of fruit characters. As most MPs are extracted from grapes during the first 24 h o u r s o f f e r m e n t a t i o n ( a n d largely in the absence of alcohol), the duration of fermentation and maceration may not play a sig- nificant role in the MP content of the final wine. 28 Whether this is true for must that contains lady beetles has not yet been deter- mined. Adding stems back during fermentation to help fix red wine color should be avoided, 12 given that about one-half of the total MP concentration in grapes is found in the stems. There is no evidence that ma- lolactic fermentation affects MP levels. 28 If fermenting or aging in oak, it is important that the wood is well-seasoned to avoid extrac- tion of green aromatic com- pounds or other constituents (such as harsh tannins) that may accentuate greenness. Well-sea- soned, medium-toast oak chips are, in fact, effective as a masking agent for a range of herbaceous and green notes characteristic of high-MP wine. 19 Fining and other additives Micro-oxygenation involves the injection of small, controlled quantities of oxygen into wine, mainly to moderate the tannin content. Anecdotally, it has also been reported to reduce green- ness, although there is little evi- d e n c e i n t h e p e e r - r e v i e w e d literature supporting this. How- ever, the observation is wide- spread enough in the industry to suggest it is real. What (if any) aromatic compounds are being altered to explain this purported effect remains to be determined. It is possible that it is largely psy- chological (which makes it no less important). By altering some of the harsh tannins associated with fruit that has not achieved optimal ripeness, the greenness Data shown are average intensity scores from a descriptive analysis of a Cabernet Sauvignon wine made from juice spiked with 30 ng/L of isopropyl methoxypyrazine. ADAPTED FROM BOTEZATU AND PICKERING (2015). REDUCTION IN METHOXYPYRAZINE CONTENT IN WINE AFTER TREATMENT WITH SILICONE AND POLYLACTIC ACID POLYMERS 25 20 15 10 5 0 Methoxypyrazine concentration (ng/L) IPMP SBMP IBMP n Control n Silicone (200 cm/L) n Poly-lactic acid (200 cm/L) Data shown are isopropyl- (IPMP), secbutyl- (SBMP) and isobutyl- (IBMP) methoxypyrazine concentrations in a red wine after six hours of treatment with polymers. The control wines received no treatment. ADAPTED FROM PICKERING ET AL. (2008). JUICE SETTLING CAN SIGNIFICANTLY REDUCE GREENNESS IN WINES 50 40 30 20 10 0 IPMP Concentration (ng/L) Unclarified Clarified with Bentonite Naturally Settled 24 Hours Naturally Settled 48 Hours Data shown are isopropyl methoxypyrazine (IPMP) concentrations ± SD in a Chardonnay juice after clarification treatments. ADAPTED FROM KOTSERIDIS ET AL. (2008). a b b c GREEN CHARACTERS IN RED WINE ARE AFFECTED BY YEAST STRAIN 1 2 3 4 5 6 7 n D21 n BM45 n D80 n EC1118 Nutty/Peanut Butter Flavour Canned Green Vegetable Flavour Canned Green Vegetable Aroma Green Pepper Aroma Earthy/Musty/ Peanut Aroma Vanilla/Caramel Aroma Red Berry Aroma Red Berry Flavour Jammy Flavour Bitter Taste Candy Aroma