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September 2016 WINES&VINES 55 PRACTICAL WINERY & VINEYARD WINEMAKING W ine tannins play a pivotal role in defining wine style be- cause they are directly responsible for sensory aspects such as astringency and bitterness; indirectly, wine tannins and their reaction products (such as polymeric pigments) modulate wine color and astringency. Seed- and skin-derived tannins differ in their chemical makeup, which affects their sensory properties. Seed-derived tannins endure a generally bad reputation with winemakers, as seeds are par- ticularly rich in monomeric flavan-3-ols that elicit bitterness, while skin tannins have higher molecular weight but would convey a rounder mouthfeel to a final wine due to their associa- tion with polysaccharides and mannoproteins. In studies conducted with model wines (simple aqueous solutions containing about 13% ethanol by volume and adjusted to pH 3.6), extractability of seed tannin into wine has been shown to decrease as grape maturity progresses. 15 As a result, picking decisions based on parameters such as seed color and so-called visual "seed maturity" have been adopted by some winemakers. The rationale is that berries with brown seeds have low ex- tractability of seed tannins and, conversely, higher extractability of skin tannins than ber- ries bearing green seeds. The need to limit seed tannin extraction into wine by delaying harvest until seeds turn uniformly brown has led to an increase of Brix levels at harvest, and concern exists that higher ethanol levels (EtOH) resulting from a high Brix level in the fruit could also favor seed tannin extraction, thereby counteracting this "late harvest-brown seeds" effect. This is be- cause an increase in EtOH during maceration may selectively promote the extraction of seed tannins due to the dissolutive effect of EtOH on the fatty outer coat of the seeds. If fruit maturity is assumed as a factor de- termining the proportion of seed- and skin- derived tannins in the finished wines, it is logical to assume that these proportions can also be adjusted during winemaking. Among many factors that govern the diffusive and dissolutive process of grape solutes during maceration, maceration length is arguably the primary factor chosen by the winemaker to modulate phenolic extraction. 6 As opposed to model wine extractions, recent research suggests that for varieties such as Cab- ernet Sauvignon and Merlot, increasing macera- tion time from 10 (traditional maceration) to 30 days (extended maceration) will achieve (under practical winemaking conditions) an amount of seed-derived tannins ranging from 50% up to 80%, respectively. 5,8,12 It is not clear however, if the reported effects of extended maceration are independent of fruit maturity and ethanol levels during winemaking. This brings about two sets of interesting questions: 1) Is visual seed maturity an actual predictor of seed tannin extraction into wine? Moreover, if seed maturity plays a lesser role in seed tannin extraction, are there other prac- tical reasons to delay harvest until seeds have turned uniformly brown? 2) Is the effect of maceration length independent of fruit matu- rity? Can ethanol enhance tannin extraction from seeds under extended maceration? Materials and methods In this study, the effects of fruit (seed) maturity, maceration length and EtOH concentration on wine phenolics, chromatic composition and sensory attributes of Merlot wines were evalu- ated. Merlot grapes (Clone 3) were harvested from the Columbia Valley AVA in Washington state at approximately 20.3 o and 24.9 o Brix in two consecutive years (2011 and 2012). Half of the low-Brix must and half of the high-Brix must were adjusted before alcoholic fermenta- tion to emulate the Brix of the other harvest. For the early harvest treatments, chaptaliza- tion with a sucrose concentrate (81 o Brix) was used to adjust the sugar level in one of the lots (average Brix at harvest: 20.35 o ± 0.1) to a target 25 o Brix without altering the total volume of the wine lot significantly (see "Experimental Design for Production of Merlot Wines"). For the late-harvest treatments (average Brix at harvest: 24.91 o ± 0.4), a portion of the must was bled off (saignée), and dechlorinated water adjusted to 4.5 g/L tartaric acid was added to emulate the soluble solids of the first harvest date (target Brix: 20 o ) without affect- ing the total volume. Each adjusted must received 10 days of skin contact (control wines) and 30 days of skin contact (extended maceration wines) to evalu- ate the chemical and sensory effects of grape maturity and different EtOH concentrations under two contrasting maceration protocols (see "Experimental Design for Production of Merlot Wines"). Fermentations occurred in triplicate in 300-liter stainless-steel jacketed fermentors fol- lowing standard winemaking practices. The winemaking protocol was as follows: Fruit was destemmed and pumped to the fermen- tors with a progressive cavity pump. Sulfur diox- ide (50 mg/L SO 2 ) was added while filling the fermentors. Fermentations occurred in 300-liter stainless-steel jacketed tanks with adjustable lids. Balancing Tannin Maturity and Extraction Studying the relationships between seed maturity, length of maceration and ethanol amount on Merlot wines By Federico Casassa and James Harbertson