A comparison between cold settling and flotation on white wine quality

Karien O'Kennedy - 26 Sep 2017

During the 2017 harvest season an experiment conducted at Groot Constantia by winemakers Boela Gerber and Rudolph Steenkamp, revealed that flotation does not harm white wine quality in any way. In fact, the wine from the tank that was clarified via flotation was incorporated into Groot Constantia’s premium Sauvignon blanc blend, whilst the settled tank’s content was assigned to the standard blend.

 

Introduction

It is the belief of some South African winemakers that traditional cold settling delivers a better quality white wine than flotation. Flotation is also often viewed as a method of clarification only used by big bulk wine producers. This perception is fast changing as more and more smaller producers also start to discover the advantages of flotation. Surprisingly there is very little scientific and popular literature available on the internet on the comparison of flotation and cold settling of grape juice. It is therefore up to winemakers to experiment themselves, in order to establish whether or not flotation can replace (or supplement) cold settling in their cellars. Flotation holds the advantages of being less time consuming, less expensive and more energy efficient than cold settling.

 

The Groot Constantia experiment

  • Sauvignon blanc grapes were harvested from the farm on the 11th of February 2017 at 21.3°Balling.
  • 35 ppm SO2 and 2 g/hl Lafazym Extract (Laffort) was added at the crusher.
  • Additional SO2 (20 ppm), 4 g/hl PVPP and 2 g/hl Lafazym CL (Laffort) were added to free run juice in the press sump.
  • The juice (only free run) was as homogenously possible divided between two tanks – 3459 l in each tank.
  • Gelatine used for flotation was Flottogel from Vason supplied by Bacchus Equipment.
  • Flotation machine used was the Juclas Easyfloat 50 from Bacchus Equipment.
  • Flotation was conducted with nitrogen gas.
  • Fermentation was conducted with 25 g/hl Anchor VIN 7.

 

Results:

 

 

Settling tank

Flotation tank

°Balling

21.9

21.8

pH

3.04

3.04

TA g/l

9.7

9.7

 

Table 1: Basic analyses (Groot Constantia and Vinlab) of the 2017 Sauvignon blanc juice before settling and flotation.

 

 

Settling tank

Flotation tank

YAN mg/l

210

200

pH

3.2

3.18

TA g/l

8.76

8.86

NTU

110

96

 

Table 2: Basic analyses (Vinlab) of the 2017 Sauvignon blanc juice after settling and flotation. (NTU was adjusted as close as possible to 100).

 

 

Settling tank

Flotation tank

pH

3.19

3.19

TA g/l

8.25

8.06

Alc. %

13.58

13.56

RS g/l

1.78

1.67

VA g/l

0.4

0.45

 

Table 3: Basic analyses (Vinlab) of the 2017 Sauvignon blanc wine after fermentation.

 

 

Settling tank

Flotation tank

3MH ng/l

226

239

3MHA ng/l

158

173

 

Table 4: Volatile thiol analyses (IGWS) of the 2017 Sauvignon blanc wine after fermentation.

 

Compound name:

Settling (mg/L)

Flotation (mg/L)

Ethyl Acetate

153.21

140.38

Methanol

68.77

67.48

Ethyl Butyrate

0.84

0.74

Propanol

42.87

36.19

Isobutanol

27.00

23.84

Isoamyl Acetate

19.20

14.71

Butanol

1.27

1.11

Isoamyl alcohol

223.70

198.05

Ethyl Hexanoate

2.02

1.84

Pentanol

0.00

0.00

Hexyl Acetate

0.29

0.26

Acetoin

1.66

0.00

3-methyl-1-pentanol

0.00

0.00

Ethyl Lactate

10.45

9.41

Hexanol

0.84

0.80

3-ethoxy-1-propanol

3.59

3.58

Ethyl Caprylate

1.03

0.93

Acetic Acid

404.24

500.67

Ethyl-3-hydroxybutanoate

0.00

0.00

Propionic Acid

2.45

2.20

Isobutyric acid

1.23

1.08

Ethyl Caprate

0.76

0.68

Butyric Acid

0.98

0.98

Iso-Valeric Acid

1.29

1.26

Diethyl Succinate

0.75

0.50

Valeric Acid

0.27

0.24

ethyl phenylacetate

0.00

0.00

2-Phenylethyl Acetate

1.40

1.24

Hexanoic Acid

8.91

8.11

2-Phenyl Ethanol

18.35

16.71

Octanoic Acid

9.56

8.73

Decanoic Acid

1.29

1.35

 

Table 5: Major volatiles (IGWS) of the 2017 Sauvignon blanc wine after fermentation (averages of two repeats).

 

Sensory analysis

Triangle testing was done by the sensory platform of the Institute for Grape and Wine Sciences, Stellenbosch University with 12 expert tasters. No significant differences between the different samples, according to the Roessler statistical tables, could be perceived at a 5% significance level. Informal tasting at Groot Constantia lead to the inclusion of the flotation wine in the winery’s reserve range.

 

Discussion

The chemical and sensory analyses conducted revealed no significant quality differences between the wines produced from the same juice via settling and flotation. These results suggest that flotation has no detrimental effect on white wine quality. In this experiment settling lead to a 9 to 13% loss of juice volume and flotation only 6 to 8%. With flotation, crushing and yeast inoculation can also happen on the same day. Apart from volume and time saving, flotation is carried out at room temperature (+/- 20°C) for best results, and is thus a significant energy saver compared to cold settling. Groot Constantia also conducted further trials on rosé, Chardonnay and Semillon during the 2017 harvest season with satisfactory results. These trials let to them purchasing the Juclas Easyfloat 50 flotation machine from Bacchus Equipment.

A study[1] conducted in Virgina, USA revealed similar results to the Groot Constantia study. The investigators also found only slight differences between the settled and floated wines with no noticeable preferences of one over the other. They did however perceive the floated wine to have slightly more overall fruit intensity.

Flotation, as with other winemaking techniques, comes with a set of guidelines that must be meticulously followed to achieve satisfactory results. Important considerations include the choice of gas (preferably nitrogen), and the quality of enzymes and floating agent used. Floating press juice might require the addition of bentonite as well.

This article reports on a single trial conducted at one winery. Possible future scientific research could shed more light on the exact short and long term differences that can possibly exist (or not) between cold settling and flotation with nitrogen gas. Winemakers not currently using flotation technology are encouraged to investigate its feasibility as there are numerous advantages attached to it.

 

Acknowledgements

Groot Constantia and the IGWS would like to thank Enrico Bocca from Enologica Vason SpA Italy, who generously lent the Easyfloat 50 (JU.CLA.S) flotation machine, through Bacchus Equipment, for this trial.

 

[1] Comparison of Juice Clarification Techniques (Cold Settling vs. Flotation) on Chemical and Sensory Aspects of Vidal Blanc

 

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