This document discusses the evolution of oak barrels and their contribution to wine aging over time. As barrels age, their permeability to oxygen decreases slightly, but the main sources of oxygen remain the bung and joints. Ellagic tannins in the wood also decrease with aging, reducing oxidation reactions. Younger barrels contribute more volatile compounds from oak, while older barrels contribute less intensely. Certain thiols linked to off-flavors decrease with barrel aging, while those linked to fruit flavors decrease more in younger barrels. Reconditioning techniques for older barrels like shaving and re-toasting only partially restore younger barrel characteristics.

1. Regeneration of oak from used barrels part 1:
Evolution of the contribution of the oak wood
barrels with their ageing
Incidence on the quality of the wines and persectives of used oak barrels
regeneration
Dr. Pascal CHATONNET
PASCAL CHATONNET CONSEIL
www.pascalchatonnet.com

2. Evolution of the contribution of the barrels
with the aging of the wood
• Oxido-reduction reactions
• Contribution of the wood to volatile and
odoriferous compounds of the wines
• Reconditionning practices

3. Evolution of oxido-reduction
with the aging of the barrels
Influence on the composition and the quality of
the wines
• Incidence on the polyphenolic compounds
and the colour of red wines
• Incidence on some particular odoriferous
compounds of the wines

4. Influence of barrel aging on the colour
of red wines
After 12 months, the colour of the wine aged in barrels is more intense and red,
After 36 months (24 months in bottle), the wine aged only in tank presents a
lower colour and a higher evolution (Tint).
* Differences in the colour stabilization
* Degradation phenomena of some pigments
New barrels Old barrels Concrete tank
Composés phénoliques after 12 months after 36 months
Anthocyanins (mg/l) 210 140 220 120 320 170
Tanins (g/l) 3 2,7 3,1 2,8 3,1 2,7
Colour intensity 0,85 0,67 0,69 0,64 0,53 0,52
Tint 0,64 0,72 0,62 0,76 0,76 0,87
after 12 months after 12 months
after 36 months after 36 months

5. Stabilisation of polyphenolics of red wine
Incidence of ageing conditions
Phenolic compounds Tank New barrel One year old Five years old
Anthocyanins (mg/l) 408 353 355 380
Tanins (g/l) 2,8 2,7 2,7 2,7
Colour intensity 0,8 1,15 0,95 0,87
Teinte 0,82 0,74 0,74 0,76
Condensed tanins 20 27 23 20
(Indice HCl %)
Combination Tanin-Anthocyanins 23 28 25 25
(Indice PVPP %)
Origin of the Red colour :
Free anthocyanins 22 16 18 20
(dAl %)
Combination Antho-Tanins 47 42 47 47
(dTA %)
Combinaisons Antho-Condensed 31 42 35 33
Tanins
(dTAT %)
78 % 84 % 82 % 80 %
after 12 months aging
With limited oxidation, the proportion of red colour
coming from free and instable anthocyanins is higher
Combination between Tannins and Anthocyanins,
promoted by moderate oxidation and synthesis
of acetaldehyde, allow a better stability of the colour
vs time

6. Influence of the conditions of ageing on the
redox potential
Tank New barrel Used barrel
240
250
260
270
280
290
300
310
320
330
Redox
potential
(mV)
• The redox potential of the wine aged in tank is significantly lower
than the wines aged in barels
• But there is no real difference of redox potential between a new
or a used barrel
280
290
300
310
320
330
340
Used barrels New barrels
RH
(mV)
Average EH top
Average EH bottom

7. Tank New barrel Used barrel
0,20
0,25
0,30
0,35
0,40
0,45
0,50
0,55
0,60
O2
dissolved
(mg/l)
Free dissolved oxigen
• Because is high reactivity in wine, it is not possible to quantify high
level of dissolved oxigen in the wines ;
• The speed of consumption of the oxigen seems reduced in the used
barrels
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
Used barrels New barrels
O2
dissolved
(mg/l)
Average 02 top
Average O2 bottom
Influence of the conditions of aging on the
dissolved oxigen in wine

8. Origine of the differences of oxidation
with the age of the barrels
• Permeability to oxigen ?
– The tanks are impermeable to oxigen ;
– The barrels are relatively permeable to oxigen ;
– With the time, the accumulation of deposits affect
slightly the gaz permeability of the barrel because the
main entrances of oxigen remain the bung and mainly
the joints between the staves ;

9. 27,5 60 12,5
0
10
20
30
40
50
60
70
Bung Joints Wood
% of Total
oxigen
Higher variability (20-35 %
~ 20-50 mg/l/year)
depending with the type of
bung and its position
(variation of vacuum)
Oxigen diffusion in a barrel

10. • Important diminution of ellagic tanins with the
aging of the barrels :
– Ellagic tanins contribute highly to the reactions of
oxidation in wine aged in barrels;
– Ellagic tanins increase the consumption of oxigen and
the redox potential of the wine
– Ellagic tanins content of oak wood decrease quickly
with the age of the barrels
• Tartrate and deposits decrease the rate of
exchange between wood and wine.

11. Evolution of the potential of ellagic tanins
with the ageing of the barrel
0
25
50
75
100
Total
Ellagic
tanins (mg/g)
0 1 2 5
0-5 mm
5-10 mm
15-20 mm
Age of the barrels (years)
• After 5 years, the ellagic tanins directly in contact with wine in the stave are
present at traces levels – The intensity of the toasting can modify the level of tanins in the
stave but also the accessibility to the deeper parts of the wood (craks).

12. Influence of Ellagic tanins on the colour of
the red wines
• Ellagic tanins promote the
copigmentation between
tanins and anthocyanins
through acetaldehyde bridges
• Increase the colour and its
stability
0
0,2
0,4
0,6
0,8
1
1,2
1,4
t = 30 jours
+ O2
t = 30 jours
+
Ellagitanins
+ O2
Aging conditions
Optical
Density
DO 620
DO 520
DO 420

13. Incidence of the age of the barrels on
some volatile and odoriferous
compounds
• Evolution of thiols involved in off-odors
• Evolution of thiols responsible for positive
« fruity » character in red wines
• Evolution of some typical components coming
from the oak wood and its toasting
• Influence of the age of the barrels on some
precursors of aroma coming from the wood

14. •The thiols contents are always higher in tank and used
barrels in relation with a higher frequency of « sulphured
off-odors »
•With the aging, the thiol content decrease highly when the
corresponding sulfurs increase except in the new oak barrels
Incidence of the age of barrel on some
thiols involved in off-odors
0
2
4
6
8
10
12
µg/l
Tank New Barrel Used barrell
sulfure d'hydrogène
méthanethiol
éthanethiol
sulfure de diméthyle
0
2
4
6
8
10
12
14
16
Cuve Barrique neuve Barrique usagée
H2S
CH3SH
C2H5SH
DMS
After 3 months aging
After 9 months aging
The oxydative phenomena
of the negative thiols
compounds are more intense
in presence of new oak

15. Influence of ellagic tanins (50 mg/l) on
Methanethiol CH3SH in a model wine solution (12
% vol. EtOH , pH 3.6)
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
24 48 72 96 144
Time of storage (h)
concentration
(µg/l)
Control
+ O2
Ellagic tanins
+O2
* The ellagic tanins of oak wood increase the disappearing of methanethiol

16. Evolution of thiols responsible for positive
« red fruit» character of red wines
OH
SH
3-mercaptohexanol
Red fruit, Black currant,
Perception threshold : 60 ng/l

17. Influence of the aging of barrels on the
3-MH content of red wines
0
100
200
300
400
500
600
700
800
900
New barrel 1 year-old 5 years-old After MLF
3-Mercapto-hexan-1-ol
(ng/l)
Strongest decrease in the wine aged in the youngest barrels in relation
with a lower « red fruit » character of the wine aged in new oak !

18. Reaction of 3-Mercaptohexanol with ellagic tanins
(vescalagine or Castalagine, 5 mg/l) in model solution (7 days,
5 mg/l O2)
400
450
500
550
600
650
700
750
C
o
n
t
r
o
l
C
o
n
t
r
o
l
+
0
2
C
a
s
t
a
l
a
g
i
n
e
C
a
s
t
a
l
a
g
i
n
e
+
0
2
C
a
s
t
a
l
a
g
i
n
e
+
0
2
+
S
0
2
V
e
s
c
a
l
a
g
i
n
e
V
e
s
c
a
l
a
g
i
n
e
+
O
2
V
e
s
a
c
a
l
a
g
i
n
e
+
O
2
+
S
O
2
3-MH
(ng/l)

19. Influence of the aging conditions on
typical compounds coming from the oak
wood
Volatile compounds Wine in tank New barrel Used barrel
Furanic by-products (mg/l) 0,22 11,1 0,31
Methyl-octalactones (µg/l) 0 230 45
4-Methyl-guaiacol (µg/l) 1 10 1
Eugenol (µg/l) 0 33 2
Vanillin (µg/l) 10 250 50

20. Evolution of typical volatile
compounds with the ageing of barrels
New barrel
1 year-old
2-3 years-
old 4-5 years-
old
S Furanic by-products
Cycloten
cis methyl-octalactone
trans methyl-octalactone
0
10
20
30
40
50
60
70
80
90
100
%
of
new
oak
potential
Age of the barrels
S Furanic by-products
Cycloten
cis methyl-octalactone
trans methyl-octalactone
Typical
compounds
Coming from the
toasting
And essentialy
present in the
Superficial parts
of the wood
Typical
compounds
influenced by the
toasting but
Naturally present
in oak wood in all
the parts of the
staves

21. New
barrel
1 year-
old
2-3
years-
old
4-5
years-
old
Guaiacol
4-Me-guaiacol
Phenol
Eugenol
Syringol
4-Me-syringol
4-Allyl-syringol
S Volatile phenols
Vanilin
0
10
20
30
40
50
60
70
80
90
100
%
of
new
oak
potential
Age of the barrels
Guaiacol
4-Me-guaiacol
Phenol
Eugenol
Syringol
4-Me-syringol
4-Allyl-syringol
S Volatile phenols
Vanilin
Typical
compounds
coming from the
toasting
dnd essentialy
present in the
superficial parts
of the wood
Typical
compounds
influenced by the
toasting but
naturally present
in oak wood in all
the parts of the
staves
Evolution of typical volatile compounds with
the ageing of barrels

22. Evolution of Aroma Precursors coming from the
oak wood with the ageing of barrels
Furfuryl thiol FFT
Perception threshold : 0,4 ng/l
O
SH

23. H2S
O CH=O O CH
OH
SH
H
+
 CH2
SH
CH
SH
O
H2O
HS
HS
+
+
Synthesis of FFT from Furaldehyde

24. 0
5
10
15
20
25
30
Furfuryl-thiol
(ng/l)
New barrel 3 years-old
barrel
Inox tank
Age des barriques
Red wine 1
Red wine 2
Influence of the use of oak wood on the FFT
content of red wines

25. Influence of the age of the barrels on the
Sensorial Description of Red Wines
(Merlot 75 %-Cabernet 25 % blend, 12 months aging)
•The Tasters = blind tasting
•33 Masters of Wines (MWI, UK)
• Five type of aging conditions :
•New french oak barrels (blend of 69
barrels)
•1 year-old barrels
•2-3 years-old barrels
•4-5 years-old barrels
•Blend (1/4)
•Sensorial analysis :
•Rating of some descriptors for each wine
(/10)
•Rating of each wine by order of
preference (/5)
•Chemical analysis

26. Rating and Preference
Tasters :
N = 33
Sum of the
Rating /
Preference
Significativity
a %
New oak 101
1 Year-old
barrel
71 Prefered
1 %
2-3 Years-old 114 Rejected
5 %
4-5 Years-old 115 Rejected
5 %
Blend (1/4) 79 Prefered
1 %

27. PCA of sensory and
chemical analysis (on
average notations)
PC2 = 20%
PC1 = 80%
FAT
VANILLA
TOASTY
OAK
TANNIC
SPICY
RED FRUIT
DMACH
index
Colour
Intensity
Tanins-Anth
combinations
Gelatine
index
Tint
HCl
index
Antho.
Ionised
Tanins/Polysaccharides
combinations
Tanins
Total Polyphenols
1 Year-old
Barrels
New
Barrels
4-5 Years-old
Barrels
2-3 Years-old
Barrels syringol
vanillin
furfural
maltol
furaneol
furfurol
4-me-guaiacol
cis Mol
trans Mol
eugenol
5-me-furfural
phenol
Ethyl vanillate 4-allyl-syringol
guaiacol
Ethyl-phenols
3-Mercapto-hexanol
Furfurylthiol

28. Prevention of alteration coming from used
barrels
- Regular and careful cleaning of the barrels (cleaning and
desinfection)
- Storage in good conditions (temperature, humidity,
absence of contamination in the atmosphere…)
- Renewal of the barrels adapted to the type of wine

29. Is-it posible to get younger the used barrels
to improve their quality ?
• Shaving of the staves ,
• Shaving and re-toasting.

30. Interest of the shaving of the used barrels?
Wood components New Barrel Used Barrel Used Barrel
Shaved
Ellagic tanins brings (mg/l) 150 15 30
Furanic by-products (mg/l) 11,1 0,31 0,27
Méthyl-octalactones (µg/l) 230 45 145
Méthyl-4-gaïacol (µg/l) 10 1 0
Eugénol (µg/l) 33 2 0
Vanillin (µg/l) 250 50 50
Preference
Of the Tasters
1 2 3
•No positive results after shaving

31. Interest of the shaving with
re-toasting of used barrels
3 years-old barrels
Oak components New Barrel Used Barrel
Used Barrel
Shaved/retoasted
Apport en ellagitanins (mg/l) 100 15 5
Dérivés Furaniques (mg/l) 8,4 0,31 0,27
Méthyl-octalactones (µg/l) 425 45 145
Méthyl-4-gaïacol (µg/l) 10 1 0
Eugénol (µg/l) 20 2 0
Vanilline (µg/l) 260 100 250
Syringaldéhyde (µg/l) 1800 80 80
S méthyl-phénols (µg/l) 7 4 26
S éthy-phénols (µg/l) 247 198 793
S diméthoxy-phénols (µg/l) 53 50 280
•A french bordelaise of 225 l contains 5 l of wine;
•The toasting of the shaved barrel increase the concentration of volatile products,
• But this toasting can produce high level of volatile phenols produced by the pyrolysis
of wine polyphenols giving off-flavours
No positive results after shaving and retoasting !
!
« burnt »
odors

32. Conclusions
• The strong changes in the oxidative phenomena
in used barrels are in direct relation with the
lower content of releasable ellagic tanins,
• The oxidative phenomena influence highly the
intensity and stability of the colour of red wines;
• The oxidative phenomena influence also highly
the aromatic evolution of the wine and in
particular the odors depending of thiols
compounds which are very sensitive to oxidative
and additive reactions in presence of ellagic
tanins

33. • The diminution of the volatile and odoriferous
contribution of oak wood depends with the origin of
the compounds (wood vs toasting) and the
localization of the molecules in the staves;
• The regular cleaning and desinfection and good
storage conditions are very important to garanty the
quality of used barrels,
• But after 4 wines, the risk to use old barrels is always
higher than the potential interest;
• The classical « reconditionning technics » used to get
younger the used barrels are very limited and can also
represent some risks for the wines.

34. • The knowledge obtained within the framework of the
study of the evolution of the oak wood contributions
with the ageing of barrels should serve for :
– To understand the reactions taking place during the ageing
of wines in barrels ;
– To optimize better the use of the wood and adapt the type
of barrel and the mode of aeging to the type of wines;
– To imagine a process of oak wood properties recovery to
improve the technological and economical parameters of
wine aged in used barrels;
– BARENA technology has been designed to regenerate
safely and economicaly these properties to guarantee the
perfect evolution of wine aged in used barrels.
•Discover the characteristics and results of the BARENA
Techoenologie in the publications to come and on
https://barena.es/