Identification of the major drivers of 'phenolic' taste in ... - GWRDC

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AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines 2 Does Phenolic Concentration Influence ‘Phenolic Taste’ in White Wine? 2.1 Introduction One early study (Singleton et al. 1975) investigated the impact of phenolic concentration on the taste properties of white wines made using a range of solids and skin fermentations. Before doing further research we investigated whether phenolic concentration did impact on the overall impression of what winemakers refer to as ‘phenolic taste’. Wines were made using currently accepted industry practices with different levels of pressings and fining treatments. Following this the phenolic content was measured and the wines tasted. The experiments were designed to elucidate to the extent of variability in sensory and compositional effects that could be expected when making white table wines using standard commercial practice. It was anticipated that these treatments would show the possible range of white table wines and give a logical basis for refinement of winemaking practices to highlight different taste profiles and styles of wine in future studies. 2.2 Methods 2.2.1 Grape Source, Juice Preparation and Fermentation Riesling grapes were machine harvested from the Orlando Wyndham St Helga vineyard in Eden Valley, South Australia in 2009. The juice was processed at the Rowland Flat winery of Orlando Wyndham Ltd and fermented at the Hickinbotham Roseworthy Wine Science Laboratory (HRWSL). Three fractions of Riesling juice were made using standard commercial practice: free run (FR), light pressings (LP) and heavy pressings (HP). These were divided into triplicate 80 L stainless steel kegs, to which pectolytic enzymes were added (Ultrazyme CPL, 3 mL/hL). Three additional 80 L kegs of HP juice were gelatine fined (Liquifine) at both 200 ppm and 1,000 ppm. All juices were cold settled for three days before being racked into new 80 L kegs. After warming to 15°C, the kegs were inoculated with PDM yeast. At the conclusion of fermentation, the wine was heat and cold stabilised, before being filled into 750 mL antique green bottles and sealed with Saran-tin ROTE screwcaps. In summary the treatments were: Page | 20 Free run (FR) Light pressings (LP) Heavy pressings (HP) Heavy pressings + 200 ppm gelatine fining (HP200G) Heavy pressings + 1000 ppm gelatine fining (HP1000G)
AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines 2.2.2 Treatments Two tasting trials were conducted. The first compared 2009 Riesling wines that were made identically from free run juice and juice from light and heavy pressings. The wines were made as described in Section 2.2.1. The second tasting compared the heavy pressing wine with those made from the same heavy pressing juice that had been fined prior to fermentation with 0.2g/L and 1.0g/L of a gelatine- based fining agent (Liquifine). These levels were chosen to represent standard and very high fining rates in a commercial context. The wines tasted had basic analysis in the following ranges: pH (3.22- 3.26), titratable acidity (6.3-6.5 g/L), alcohol (11.8-12.1% v/v) and residual sugar (0.4-0.9 g/L). This suggests that the wines were very similar in their basic structure. Page | 21 Free Run FR EW1 001-003 Receive juice from Rowland Flat Light pressings LP EW1 004-006 Heavy Pressings Settle + rack Settle + rack Settle + rack HP EW1 007-009 Add Liquifine 200 ppm HP+200ppm EW1 010-012 Figure 2-1: Schematic of winemaking (2009) 2.2.3 Tasting Conditions and Experimental Design 40 mL of wine were presented in clear ISO tasting glasses under natural light and at room temperature (23°C). While the assessment was not conducted in individual booths, the tasters did not communicate with each other during the duration of the tasting. The small number of tasting samples and tasters made it feasible to present the samples in an order which could control for possible presentation order effects resulting from bitterness carry-over between samples. A cross-over experimental design whereby each sample is tasted after each other sample the same number of times, and each sample appears in the same position the same number of times was used to this end. Add Liquifine 1000 ppm Settle + rack Settle + rack HP+1000ppm EW1 013-015
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Identification of the major drivers of 'phenolic' taste in ... - GWRDC

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