Climate and variety impact cold soak effectiveness

Page last updated: Monday, 14 September 2020 - 10:26am

There is a general perception that pre-fermentative cold maceration or ‘cold soak’ improves colour, enhances fruit characters and provides complexity to red wines. A trial conducted in 2013 examined the influence of climate and variety on the effectiveness of pre-fermentative cold maceration.

Background

Pre-fermentative cold maceration or ‘cold soak’ is a commonly practiced red winemaking technique. The technique involves inhibiting the onset of fermentation by holding the must at temperatures typically under 15°C for a period of days. During this period, an aqueous extraction, as opposed to the alcoholic extraction, of compounds from the skins occurs.

There is a general perception that a cold soak improves colour, enhances fruit characters and provides complexity to red wines.

Anecdotal evidence suggests that cold soaks are best utilised under certain conditions relating to climate and variety, this study is the first of its kind to examine these two variables concurrently.  

Aim

To investigate the influence of climate and variety on the effectiveness of  cold soaking.

Trial design

In 2013, fruit was selected from vineyards in two distinct Western Australian wine regions, Swan District (hot) and Great Southern (cool). The climates of these can be characterised by mean January temperature (MJT); in 2013 the MJT’s of the regions were 24.9°C and 19.7°C respectively.

From each region, 100 kilogram parcels of Shiraz, Cabernet Sauvignon and Merlot were hand harvested.

Each parcel of fruit was split into treatments, ‘control’ (Ctrl) and ‘cold soak’ (CS). Each treatment was then divided into three equal lots creating three replicates.

The winemaking process was the same for all treatments except the must of the CS parcels were stored at 4°C for 5 days prior to the commencement of fermentation.

Sensory analysis

Sensory panel

Descriptive sensory analysis was performed at two and at nine months after bottling. Each sensory session was conducted following the same procedure; nine experienced winemakers made up the panel, two replicates were included for each treatment, wines were presented in unique randomised order grouped into regional and variety brackets.

A simple linear regression provided a 5 – 10% level of significance (P < 0.05 – 0.1) for the sensory data.

Results

Colour

Table 1 shows the colour analysis of the wines at two time periods; two months after bottling (T1) and nine months after bottling (T2). A percentage of difference is used to indicate the degree of influence the cold soak treatment has when compared to the control.

Hot Shiraz

Control

Cold Soak

% difference

Colour density T1

7.75

6.76

-12.77

Colour density T2

7.86

6.72

-14.45

Colour  hue T1

0.72

0.77

7.91

Colour  hue T2

0.69

0.75

7.97

Total phenolics (a.u.) T1

42.43

37.48

-11.67

Total phenolics (a.u.) T2

41.25

36.00

-12.74

Total anthocyanins (mg/L) T1

265.32

210.92

-20.5

Total anthocyanins (mg/L) T2

197.89

158.75

-19.78

Cool Shiraz

Control

Cold Soak

% difference

Colour density T1

9.11

9.67

6.22

Colour density T2

8.35

8.84

5.87

Colour  hue T1

0.56

0.58

3.57

Colour  hue T2

0.60

0.62

2.5

Total phenolics (a.u.) T1

39.93

41.08

2.87

Total phenolics (a.u.) T2

35.85

36.70

2.39

Total anthocyanins (mg/L) T1

494.64

491.56

-0.62

Total anthocyanins (mg/L) T2

342.53

341.57

-0.28

Hot Cabernet

Control

Cold Soak

% difference

Colour density T1

4.41

5.68

28.9

Colour density T2

3.95

5.72

44.81

Colour  hue T1

0.82

0.73

-10.2

Colour  hue T2

0.69

0.74

6.52

Total phenolics (a.u.) T1

32.06

31.01

-3.25

Total phenolics (a.u.) T2

28.67

29.89

4.24

Total anthocyanins (mg/L) T1

255.99

246.73

-3.62

Total anthocyanins (mg/L) T2

171.50

188.82

10.1

Cool Cabernet

Control

Cold Soak

% difference

Colour density T1

8.64

8.95

3.59

Colour density T2

8.77

8.07

-8.04

Colour  hue T1

0.63

0.61

-3.7

Colour  hue T2

0.67

0.65

-2.26

Total phenolics (a.u.) T1

34.92

36.20

3.68

Total phenolics (a.u.) T2

32.37

32.31

-0.17

Total anthocyanins (mg/L) T1

429.55

432.45

0.68

Total anthocyanins (mg/L) T2

297.55

295.76

-0.6

Hot Merlot

Control

Cold Soak

% difference

Colour density T1

6.74

7.30

8.31

Colour density T2

6.66

7.41

11.34

Colour  hue T1

0.74

0.74

0

Colour  hue T2

0.73

0.75

2.76

Total phenolics (a.u.) T1

39.06

37.48

-4.05

Total phenolics (a.u.) T2

36.96

37.46

1.37

Total anthocyanins (mg/L) T1

310.06

249.07

-19.67

Total anthocyanins (mg/L) T2

263.22

210.19

-20.15

Cool Merlot

Control

Cold Soak

% difference

Colour density T1

7.91

7.36

-6.95

Colour density T2

7.05

6.79

-3.76

Colour  hue T1

0.58

0.60

2.29

Colour  hue T2

0.63

0.65

3.2

Total phenolics (a.u.) T1

33.54

33.24

-0.9

Total phenolics (a.u.) T2

29.84

29.94

0.35

Total anthocyanins (mg/L) T1

418.74

416.70

-0.49

Total anthocyanins (mg/L) T2

280.34

266.08

-5.09

Observing a 10% difference between treatments as notable, only differences in hot climate wines were found. Results show cold soaking hot climate Cabernet dramatically increased colour density by 44.81% after nine months in bottle.

Cold soak reduced total anthocyanins in hot climate Merlot but colour density was increased. Cool climate Shiraz, Cabernet and Merlot showed little difference between treatments suggesting the influence of climate to be greater than variety when considering colour.

Sensory assessment

The following figures illustrate the results of the sensory assessment of the treatments at both two and nine months post-bottling. Red and blue lines represent Ctrl and CS treatments respectively. Statistical differences (P value ≤0.05) by attribute are identified by **.

Initially, hot climate Shiraz wines without cold soak had greater dark berry aromas, palate length and tannin however these differences weren’t found after a total of nine months in bottle (Figure 1). Cool climate Shiraz showed no significant difference for any attributes over the two time periods (Figure 2).

Figure 1 Effect of both cold soak and time on wine attributes for hot climate Shiraz
Figure 1 Effect of both cold soak and time on wine attributes for hot climate Shiraz
Figure 2 Effect of both cold soak and time on wine attributes for cool climate Shiraz
Figure 2 Effect of both cold soak and time on wine attributes for cool climate Shiraz

Sensory properties of the hot climate Cabernet were significantly influenced by the cold soak treatment with colour (depth and hue), aroma (chocolate) and palate (weight, texture and length) attributes enhanced by the cold soak and persistent over both sensory sessions (Figure 3).

Figure 3 Effect of both cold soak and time on wine attributes for hot climate Cabernet Sauvignon
Figure 3 Effect of both cold soak and time on wine attributes for hot climate Cabernet Sauvignon

 The only significant difference in cool climate Cabernet was CS hue being greater than Ctrl nine months post-bottling (Figure 4).

Figure 4 Effect of both cold soak and time on wine attributes for cool climate Cabernet Sauvignon
Figure 4 Effect of both cold soak and time on wine attributes for cool climate Cabernet Sauvignon

Hue in hot climate Merlot was consistently rated higher in the Ctrl over the two periods (Figure 5).

Figure 5 Effect of both cold soak and time on wine attributes for hot climate Merlot
Figure 5 Effect of both cold soak and time on wine attributes for hot climate Merlot

Cool climate Merlot showed stylistic differences initially with cold soak enhancing flavour and texture but less confectionery and red berry aromas than the control. These differences were not observed at nine months (Figure 6).

Figure 6 Effect of both cold soak and time on wine attributes for cool climate Merlot
Figure 6 Effect of both cold soak and time on wine attributes for cool climate Merlot

Findings from this study are limited to one growing season. To extend this trial for multiple seasons and increasing the number of replicates would provide additional confidence; replicating the trial on a commercial scale is also suggested.

Conclusion

Cold soak is not a ‘one size fits all’ technique and is more effectively utilised under specific conditions.

The quality of hot climate grown Cabernet greatly benefits from the application of a cold soak with improved colour and palate structure. Cool climate Cabernet had little change after a cold soak.

Shiraz did not respond positively to cold soaking regardless of climatic region in which the fruit was grown. The quality of hot climate wines was reduced when treated with a cold soak.

In terms of wine style, it was initially observed a cold soak on cool climate Merlot provided palate complexity compared to a fruit forward style without it, however, after nine months there were no sensory differences. The only descriptor that showed significant differences between treatments in the sensory assessment was colour.

This study has demonstrated that not all varieties react similarly to a cold soak and the climate in which the fruit has been grown can influence the impact of this technique. Winemakers should consider climate and variety when practicing this technique to avoid unnecessary inputs for little return on wine quality.

Acknowledgments

This study was carried out with the financial support from Australia’s grapegrowers and winemakers through their investment body, Wine Australia.

Thanks to Department of Agriculture and Food WA staff Andrew Taylor, Glynn Ward, Kristen Brodison, Karryn Reeves and Rebecca O’Leary for their valuable assistance.

Contact information

Richard Fennessy
+61 (0)8 9780 6219

Author

Richard Fennessy