The extraction of tannins using different winemaking techniques (Part 1)

Full text

The extraction of tannins
using different winemaking
techniques (Part 1)
WineLand August 2014
Keywords: Tannins, BSA, MCP.
Anton nel1, Pierre vAn rensburg2 &
MArius lAMbrechts2
1 Cape Institute for Agricultural Training (CIAT), Elsenburg
2 Distell, Stellenbosch
Introduction
Tannins consist of a set of monomers named catechins, epicatechins,
epigallocatechins and epicatechin-gallate (Kennedy et al., 2000b).
These monomers occur in different polymeric lengths in the skin and
seed of the grape berry (Kennedy et al., 2000b; Downey et al., 2003).
There is also a difference in the composition of monomers between
skin tannins and seed tannins. Only seed tannins contain epicatechin-
gallate.
The importance of tannins was underestimated for a long time.
With the development of newer vinification technology, the value of
tannins has become increasingly apparent. It is currently known that
tannins are important in wine for taste (bitterness) (Monagas et al.,
2005), mouthfeel (astringency) (Gawel, 1998; Monagas et al., 2005),
stabilisation of colour (Monagas et al., 2005), maturation potential
(Lorenzo et al., 2005) and health (Cordier, 2007).
The grapevine has a genetic ability to synthesise tannins, but this
ability is largely influenced by environmental factors. Factors such
as day and night temperatures (Jackson & Lombard, 1993; Mori et
al., 2005 & Tarara et al., 2008), sunlight (Kennedy et al., 2000 and
Pastor del Rio & Kennedy, 2006) and water stress (Hardie & Consi-
dine, 1976 and Matthews & Anderson, 1988) impact on tannin syn-
thesis. Other factors that come into play are slope, aspect, cultivar,
terroir etcetera.
Once nature and the viticulturist have played their part to increase
the tannin concentration in the grapes, it is the winemaker’s turn to
use various techniques to extract these tannins from the grapes. Dif-
ferent techniques may be employed, each producing different end
results. The most controversial method is cold soaking, which was
developed in the mid-1980s to extract colour from Pinot noir.
FIGUUR 1. Verskillende monomere waaruit tanniene gebou word.
balling
LB
balling
HB
Farm: Plaisir de Merle
Treatment
C
PM
CM
CM+PM
E
200
400
600
800
1000
1200
1400
1600
1800
2000
Tannin (mg/L)
Farm: Morgenster
Treatment
C
PM
CM
CM+PM
E
ab
c
de
ac
abf
cf
de
cf
bdg
cf
e
afgh
abf
ch
de
c
ch
i
bd
ch
FIGUUR 2. Die gemiddelde tannienkonsentrasie van Cabernet Sauvignon van
die twee plase soos gepars in 2009.
FIGURE 1. The different monomers of which tannins are composed.

A
v
A
i
l
A
b
l
e
n
o
W
!
Crushed grapes are chilled for a certain period, usually three or more
days, at 10°C at least (Gomez-Plaza et al., 2000). This is supposed
to extract colour from the skins. For extended skin contact the skins
are left on the wine for a further two weeks so that the alcohol in the
wine will extract more tannin from the skins and seeds (Joscelyne &
Ford, 2008). With thermovinification the skins and juice are heated
to 60 - 80°C for 20 - 30 minutes (Ribereau-Gayon et al., 2000). Dur-
ing this heating stage the cell walls are broken, thereby releasing the
tannins and anthocyanins. Whole bunches may also be fermented
(carbonic maceration) thus producing fruity wines, with less tannins
(Sacchi et al., 2005). Other methods are also available such as the
addition of enzymes (Arnous & Meyer, 2009) and sulphur (Spagna
et al., 2003).
The old adage holds true therefore, that something which can be
measured, can be managed. Various methods are available to measure
phenols and also tannins specifically. The most popular methods
currently to measure tannins are precipitation methods. Californian
BSA (bovine serum albumin) uses a protein to bind to the tannins and
the MCP (methylcellulose) method uses a polysaccharide to bind to
the tannins. These two methods were used in this study.
Material and method
Two farms in different climatological areas were chosen for this
study. One of these (Morgenster) is situated in a Winkler scale III and
is called the cooler farm. The other farm (Plaisir de Merle) is in situ-
ated in a Winkler scale IV and is called the warmer farm. Two culti-
vars were used, namely Cabernet Sauvignon (CS) and Shiraz (SH).
The two cultivars were crushed at two degrees of ripeness, namely
before the commercial harvest (LB) and after the commercial harvest
(HB).
Five different vinification treatments were used. The treatments
are the following:
• Control (C) – the grapes were crushed, inoculated with WE372
and pressed at the end of fermentation.
• Enzyme treatment (E) – as for the control, except that a pecto-
lytic preparation was used.
• Cold maceration (CM) – the crushed skins were held at 10°C for
three days before the grapes were inoculated with WE372. After
fermentation the grapes were pressed.
• Post maceration / extended skin contact (PM) – crushed grapes
were inoculated with WE372 and after fermentation the skins
were left on the wine for a further two weeks before being
pressed.
• Combination of cold maceration and post maceration (CM + PM)
– crushed skins were kept at 10°C for three days before the grapes
were inoculated with WE372. After fermentation the skins were
left on the wine for a further two weeks before being pressed.
Tannins were measured by making use of the BSA and MCP meth-
ods.
Results
According to Figure 2 the tannin concentration of the Cabernet Sau-
vignon CM treatment, of the LB on both farms, had a negative effect
compared to the control. In the HB no treatment had any effect on
tannin concentration (Figure 2), except that the CM treatment showed
a negative effect on the cooler farm (Figure 2). The only treatment
FIGUUR 1. Verskillende monomere waaruit tanniene gebou word.
balling
LB
balling
HB
Farm: Plaisir de Merle
Treatment
C
PM
CM
CM+PM
E
200
400
600
800
1000
1200
1400
1600
1800
2000
Tannin (mg/L)
Farm: Morgenster
Treatment
C
PM
CM
CM+PM
E
ab
c
de
ac
abf
cf
de
cf
bdg
cf
e
afgh
abf
ch
de
c
ch
i
bd
ch
FIGUUR 2. Die gemiddelde tannienkonsentrasie van Cabernet Sauvignon van
die twee plase soos gepars in 2009.
FIGURE 2. The average tannin concentration in Cabernet Sauvignon from the two farms as crushed in 2009.

balling
LB
balling
HB
Farm: Plaisir de Merle
Treatment
C
PM
CM
CM+PM
E
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
Tannin (mg/L)
Farm: Morgenster
Treatment
C
PM
CM
CM+PM
E
abc
d
ab
ef
ac
d
b
efg
ce
dh
abc
ef
acg
eh
ab
cf
eh
i
ef
d
FIGUUR 3. Die gemiddelde tannienkonsentrasie van Shiraz van die twee
plase soos gepars in 2009.
Vir verdere inligting kontak Anton Nel by antonn@elsenburg.com.
FIGURE 3. The average tannin concentration in Shiraz from the two farms as crushed in 2009.
that showed a significant effect in tannin concentration is the E treat-
ment (Figures 2 and 3).
Figure 3 shows that the CM treatment had a positive effect on the
tannin concentration of Shiraz in the LB on both farms, although the
increase is not significant. No treatment had any effect in the HB,
except for the CM + PM treatment which showed a negative effect
on tannin concentration. Once again the E treatment showed the most
significant increase in tannin concentration. A major reason why
enzymes have such a significant effect on tannin extraction is that
enzymes break down the combinations between tannins and cell wall
components, thereby causing more tannin to be extracted (Arnous &
Meyer, 2009).
Interestingly the BSA method displayed the same trends as the
MCP method (data not shown). The E treatment is also indicated by
this method as the treatment able to extract the most tannin from the
skins and seeds.
Conclusion
The winemaker has various techniques at his/her disposal to extract
tannins in the wine. For techniques such as cold soak, time is a pre-
requisite. In cold soak the skins must be left on the juice for a mini-
mum of three days. The cost of cooling must be taken into account.
During extended skin contact the skins must be left on the wine for
at least two weeks. During this period the wine is by no means pro-
tected against micro-organisms and oxygen and the wine is suscep-
tible to becoming oxidised and the volatile acid (VA) may even
increase as a result of spoilage organisms. Space may also become a
problem seeing that these techniques require the skins and juice/wine
to be left in tanks and during the crush there is usually much jostling
for tank space.
This study showed that the treatments had no significant effect on
tannin concentrations. The only treatment that showed a significant
effect was the enzyme (E) treatment. By making use of pectolytic
enzymes, the tannin concentration in the wine may increase.
As with any study, questions arise that may be addressed in future
by further study. The study showed that extended skin contact did not
have a significant effect. The wines were not treated with enzymes
either. The question is therefore posed about the effect of using
extended skin contact together with pectolytic enzymes.
Acknowledgement
Winetech for funding the study and Distell for the infrastructure.
Thanks also to the personnel at the Distell experiment cellar and the
respective farms that sacrificed their grapes.
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Summary
Tannin is very important in wine as it contributes to taste (bitterness), mouth feel (astringency), colour stability, maturation potential
and has health benefits. Although there are a couple of things that a viticulturist can do to enhance the tannin concentration in the grapes,
the most important effect is dependent on environmental factors. This study was done on two farms: a cooler farm (Winkler scale III)
and a warmer farm (Winkler scale IV). Cabernet Sauvignon and Shiraz were harvested at two different ripeness levels, namely before
commercial harvest (LB) and after commercial harvest (HB). This study shows that no winemaking techniques had a positive effect on
tannin concentration except for the use of pectolytic enzymes.
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