Winetech Technical Yearbook 2022

16

14

12

10

8

6

Guaiacol (µg/L)

4

2

0

QA 23 BM4x4 AWRI R2 Rhone4600 Cross evol. Alchemy II

VIN 7 Spont. Ferment

BDX

UOA Maxithiol

X5

VIN 13

X16

Yeast treatment FIGURE 1. Guaiacol levels in laboratory-scale Chenin blanc wines produced from smoke-exposed juice fermented with selected commercial yeasts or spontaneous alcoholic fermentation (Spont. Ferment).

14

12

10

8

6

4-Methylguaiacol (µg/L)

4

2

0

QA 23

AWRI R2

VIN 7

Alchemy II

Rhone4600

BM4x4

Cross evol.

BDX

X5

Spont. Ferment UOA Maxithiol

X16

VIN 13

Yeast treatment

FIGURE 2. 4-Methylguaiacol levels in laboratory-scale Chenin blanc wines produced from smoke-exposed juice fermented with selected commercial yeasts or spontaneous alcoholic fermentation (Spont. Ferment).

MATERIALS AND METHODS A selection of 12 commercial yeasts was evaluated in laboratory scale (200 mL) fermentation trials using smoke-exposed Chenin blanc juice. This was followed by a small-scale (14 L) wine production trial with smoked and unsmoked Chenin blanc juice with a selection of three yeasts, namely QA23, VIN 13 and X16. Wines produced from the smoke-exposed juice will be referred to as smoked wines. The concentrations of the volatile phenols were determined, and the wines were also subjected to sensory evaluation. RESULTS AND DISCUSSION The guaiacol and 4-methylguaiacol levels varied in the laboratory scale Chenin blanc wines produced with the different yeast strains (figure 1 and 2). Wines made with the yeast QA23 contained the highest guaiacol and 4-methylguaiacol levels, while wines fermented with VIN 13 and X16 contained the lowest levels. All the other treatments ranged somewhere in between, but not in

the same order for the two compounds. QA23 is known to have β -glucosidase activity, a desired trait that helps release varietal aroma compounds. In this case, it can also increase the volatile phenol levels in wine by liberating them from their glycoconjugate form. In the small-scale trial, wines produced from unsmoked and smoked juice fermented with QA23, VIN 13 and X16 were compared. The wines produced from the smoke-exposed juice contained notably higher levels of guaiacol and 4-methylguaiacol than the unsmoked treatments (figure 3). As with the laboratory scale trial, smoke-exposed juice fermented with QA23 had the highest guaiacol levels and those fermented with VIN 13 the lowest. However, X16 also produced similar high guaiacol levels as QA23 in the Chenin blanc wines produced from smoke-exposed juice. The 4-methylguaiacol levels in all the smoked wines were well below the detection threshold and relatively similar for all three yeasts. The volatile phenol levels in these experiments were not as high as those found in some commercial wines produced from grapes exposed to wild or vineyard fires. Still, the sensory

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WINETECH TECHNICAL YEARBOOK 2022