Harvesting Shiraz grapes at the optimal maturity is critical for achieving the targeted wine style, however challenges such as unexpected viticultural/climatic conditions and/or the availability of resources can force producers to harvest the crop earlier than originally planned. This has a significant impact on the composition and the quality of the resulting wines and the question is: What options are available to the producer to improve the sensory characteristics under these circumstances?

A research study titled, “Use of Winemaking Supplements To Modify the Composition and Sensory Properties of Shiraz Wine1” aimed to explore the options available to mimick mouthfeel characters typically found in wines made from riper grapes. A selection of additives was tested by comparing wines made from earlier harvested grapes plus the additive to wines made from later harvested grapes. The study specifically focussed on the effects of the additives on the tannin, mannoprotein and polysaccharide content of the wine as well as the colour and sensory impact.

 

Materials and Methods

Shiraz grapes were sourced from the McLaren Vale region in South Australia (more information on the regional climate is available in the publication).

 

The grapes were harvested at two time points: 

(A)       Early harvest (5 February)

23.9 °Brix and pH 3.4

(B)       Later harvest (11 February)

27.7 °Brix and pH 3.7

 

The early harvest grapes (A) were divided into seven different treatments (see below). Harvest (B) grapes were vinified as specified in (1) below, however, the pH was adjusted to 3.6 by adding 2 g/L tartaric acid.

 

1. Control
The wine was made by inoculating 30 g/hL EC1118 yeast (Lallemand) immediately after crushing and fermented at 28°C with the cap plunged twice daily. DAP was added on the first and third day after inoculation. After seven days, the wines were pressed and transferred to 5 L glass demijohns and fermented to dryness (<1 g/L glucose and fructose). Before cold stabilization, 60 mg/L of potassium metabisulfite was added to the wine. Following cold stabilization, 30 mg/L of potassium metabisulfite was added. No malolactic fermentation took place. The wines were bottled under screwcap and stored at 15°C for three months after which chemical and sensory analyses took place.

2. Cold Soak (CS)
The must was stored at 10°C for 61 hours before inoculation. Vinification proceeded as specified in (1).

3. Cold Soak + Enzymes (CS+E)
Vinification took place as specified in (2), with the addition of a maceration enzyme (Laffort HE Grand Cru at 72.6 mg/kg fruit) before inoculation.

4. Cold Soak + Enzymes + Mannoproteins (CS+E+MP)
Vinification took place as specified in (3), with the addition of mannoproteins (Mannoprotein Laffort Oenolees at 300 mg/L) after racking from the gross lees.

5. Tannin (T)
Vinification took place as specified in (1), with tannin addition during the first punch-down (Laffort blend 1:1 of VR COLOR and VR SUPRA at 400 mg/L; applied according to the manufacturer’s instructions).

6. Mannoprotein (MP)
Vinification took place as specified in (1), with the addition of mannoproteins (Mannoprotein Laffort Oenolees at 300 mg/L) after racking from the gross lees.

7. Tannin + Mannoprotein (T+MP)
Vinification took place as specified in (5), with the addition of mannoproteins (Mannoprotein Laffort Oenolees at 300 mg/L) after racking from the gross lees.

 

Results

Naturally, the alcohol concentration between the wines (A) control and (B) was different with 14.0% and 16.7%, respectively. The wines from (B) also had a marginally higher titratable acidity (TA) (8.1 g/L) compared to (A) control (7.4 g/L) due to the addition of tartaric acid. The glycerol in (B) was 12.41 g/L compared to 9.79 g/L in (A). These differences will undoubtedly affect the wine’s sensory composition. The study aimed to investigate the effectivity of the additives to create a wine resembling (B).

For the purpose of this blog post, only the results from the sensory analyses will be reported here, however, the publication elaborates on the chemical composition of the wines including the impact of the additives on the tannin, mannoprotein and polysaccharide content of the wine as well as the colour.

 

Sensory analysis

The judges were asked to score the wines based on the intensity of a list of ten given attributes.

 

  • The wine made from later-harvested fruit (B) showed the highest intensities of “dark fruit”, “flavour intensity”, “jammy”, “sweetness”, “palate fullness” and “hotness”.
  • CS+E was scored the highest in “astringent” and “coarse” on the palate compared to all the other wines, (A) and (B).
  • CS+E+MP failed to significantly modify the astringency and was scored similarly to CS+E. The wine did, however, score higher in “palate fullness” and “hotness” compared to CS+E.
  • Interestingly, T did not give rise to any changes in tannin concentration and composition (chemical analyses) and sensorially, the wine scored similarly to (A) control for attributes “astringency” and “coarseness”. T scored the highest in the intensity of “red fruit” and “confectionary” aroma compared to all the other wines, (A) and (B).
  • Of all the (A) wines, T+MP had the closest resemblance to the later-harvested wine (B). T+MP showed the highest intensity of “dark fruit” aroma, “flavour intensity” and “jammy” of all the (A) wines while the intensity of the most of the other attributes was relatively close to that of (B).
  • MP decreased the tannin concentration (chemical analyses) and the intensity of “astringent” and “coarse” mouthfeel when compared to (A) control. In fact, MP was rated as the least “coarse” wine of all the wines tested, (A) and (B). The wines with MP showed similar intensities of “red fruit” aroma compared to T (which were rated highest).

 

A rough subjective grouping of the wines into three groups according to the similarity:

  • (B) and T+MP
  • (A) control and CS
  • T and MP
  • CS+E and CS+E+MP

 

Sensory Interactions

There is much to be said for complex interactions between various inherent and added wine constituents. The addition of a product might not have the desired effect on the wine sensory composition due to interactive effects or the modification of multiple wine components at once. These effects can unfortunately not be isolated due to the complexity of the wine matrix. The nature of the additive and the natural composition of the wine will ultimately determine the effectivity of the additive to provide the desired effects and will most likely differ from one wine to the next. It is therefore important to do bench trials (where possible) to ensure the desired product is achieved with any unique wine.

 

Conclusion

In this specific study, the addition of oenological tannins and mannoproteins to earlier harvested grapes/wine resulted in a closer resemblance to the style obtained by wine made from “the same” grapes harvested at a later stage. Even though none of the (A) wines was able to completely reach the sensory qualities delivered by the later harvested grapes, it is evident that various options exist to significantly improve the sensory perception of wines made from grapes harvested at an earlier stage.

These tools can also be used to the producer’s advantage in cases where lower alcohol wines are to be produced due to health-conscious consumers and/or effects of climate change causing earlier optimal aroma development necessitating an earlier harvest.

 

References

(1)      Li, S.; Bindon, K.; Bastian, S. E. P.; Jiranek, V.; Wilkinson, K. L. Use of Winemaking Supplements to Modify the Composition and Sensory Properties of Shiraz Wine. J. Agric. Food Chem. 2017, 65 (7), 1353–1364. https://doi.org/10.1021/acs.jafc.6b04505.

 

Photo by Rodrigo Abreu on Unsplash