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Flextank HDPE
Maturation Vessels;
Australian & International Trial Updates
The
Flextank controlled permeation tanks for wine maturation have
been used increasingly widely in Australia over several years.
International sales are also increasing. The following reviews
the concept of Flextank maturation vessels and summarises the
outcomes of recent wine trials carried out in Australia and
Europe. The results of these trials clearly show that taint,
so often a criticism leveled at 'plastic' tanks, is not an issue
with wine stored in Flextanks. The trials also confirm that
Flextanks equal or exceed oak barrels for wine maturation for
quality wine development. For best results, emphasis must be
placed on the selection, origin, number and use of the oak used
in the Flextanks, considerations similar to barrel selection.
The ability to tailor vessels with specific oxygen permeation
rates to suit a particular wine style is described.
FLEXTANK
USES A POLYMER THAT IS INERT:
The
selection of the thermoplastic polymer used by Flextank
is the result of substantial theoretical and trial work:
it is an ultra-clean, food grade high-density polyethylene
that has received approval for liquid food and wine use
specifically. It has also been extensively trialled. The
materials development process also required consideration
of each production step to ensure that the polymer had the
right sinter density and was not degraded during the moulding
step. Other considerations included lifespan of the products
and ease of use aspects such as internal surface finish
and tartar non-adhesion. The precise makeup of the Flextank
polymer is commercially sensitive.
Tanks
made more than twenty years ago were in fact not thermoplastic,
but were actually made from thermosetting polyester resin
mixed with glass fibres. The solvents and catalysts used,
if extracted into wine, could lead to a distinct taint.
Food grade thermoplastic polymers like polyethylene are
a different material entirely. They contain no free solvents
or other reagents that can migrate into wine.
The
absence of taint in wine stored in Flextank maturation tanks
has been confirmed by winemakers from various trials with,
in one case, the wine being stored for three years. Not all
trials are fully replicated and this always limits the depth
of information that can be extracted from the data. But, in
the words of one Australian winemaker, "we found that
they (Flextanks) don't taint".
Chemical
analysis of wine stored in Flextanks has shown that there
is no difference in the general wine quality parameters for
wine stored in Flextank, oak or stainless steel. Of particular
note, chlorophenols, a concern often expressed with the use
of plastic materials in wine production, were not found in
Flextank-matured wine.
WINE
TRIALS IN AUSTRALIA:
Flextank
maturation tanks require the addition of oak to allow the
wine to develop oak-derived flavours that occurs in the
barrel maturation process. High quality staves are recommended
for this process. Further, the Flextank maturation process
with staves will be less at risk from other problems, including
losses due to evaporation and development of Brett off-flavours,
than can occur during oak barrel maturation.
On
the other hand, if oak staves are not added to the wine
in Flextanks, the maturation process becomes similar to
that occurring in a neutral or spent barrel: the advantage
of Flextank maturation, apart from much improved hygiene
over use of old barrels, is that oxygen ingress is closer
to that of a new barrel, allowing wine development to occur
to a more normal timetable.
TRIAL
1:
A
2006 Shiraz, after malo-lactic fermentation, was added to
the following vessels:
-
3 x new American oak hogsheads
-
2
x 1000 Litre Flextanks, each containing one 'Flextank
8 QP' modular oak stave pack
-
3
x 2100 Litre Flextanks, each containing two 'Flextank
8 QP' modular oak stave packs
All
vessels were kept in the same storage area (same temperature
and humidity) for the eleven months duration of the trial.
The intention of the trial was to monitor relative changes
in various chemical parameters for the wines stored in the
different vessels.
Free
sulfur dioxide concentration (mg/litre) in 2100 litre Flextanks
(BP01, BP02, BP03), 1000 litre Flextanks (BP05, BP06)
and new
American oak hogsheads over 5 months.
The
free sulfur dioxide concentrations were essentially the
same in all storage vessels after the 11 month maturation
period. Importantly, the rate of free sulfur dioxide loss
in the first five months occurred at the same rate for the
oak and Flextank vessels, showing the validity of Flextank's
oxygen permeation physics and vessel designs.
There
was no significant difference in wine colour density after
11 months, while the wine hue was higher in the Flextank
vessels in comparison to the oak vessels. Levels of oak
volatiles increased during the time course of the maturation
study, irrespective of storage vessel type.
The
concentrations of free dimethyl sulfide in the Flextank
vessels were slightly, but not significantly, higher than
in the oak vessels (8 to 10 microgram/litre compared to
6 microgram/litre). The measured concentrations of hydrogen
sulfide were the same in all vessels and the levels of methanethiol
were below detection.
TRIAL
2:
This
trial focussed on maturation of a 2007 Shiraz wine with
subsequent sensory assessment for classification into wines
for two retail price points: $40 and $15. The wine was stored
in the following vessels for 7 months of maturation:
-
2nd
fill French oak hogsheads
-
-
Flextank
with oak staves 2,000 l with French oak staves
-
-
Stainless
steel tanks with French oak staves
The
resulting wines were assessed blind by 5 winemakers using
the International 20 point scoring system (maximum score
= 20). The
results were:
-
Price
point $15: Flextank 18/20; stainless steel 14/20; oak
hogsheads 13/20
-
Price
point $40 (trial 1): Flextank 18/20; Stakvat 17/20; hogsheads
9/20
-
Price
point $40 (trial 2): Flextank 16/20; hogsheads 14/20;
foudre 11/20; Stakvat 9/20
The
results of this trial clearly demonstrate the success of
Flextank vessels for the maturation of high value wine.
TRIAL
3:
A
2008 vintage Shiraz was placed in several different vessels
near the end of the primary ferment for 4 months maturation.
The vessels used were:
-
Barriques
(2nd fill Francois Freres)
-
Flextank
1,000 litre with mixed French staves
-
The
wines were tasted for allocation by five winemakers and
scored using the International 20 point scoring system.
The wine in Flextank received a 'gold medal' (that is, a
score of 18.5/20 or higher), the wine in barriques received
a 'silver medal' and that from the stainless steel, a bronze
medal.
In
both of the above trial cases the winemakers judged the
wine matured in Flextank to exceed the quality of the wine
matured in French oak barrels. The outcome of both trials
confirmed the ability of Flextank vessels to mature wine
destined for the even the top price points in the market
place.
WINE
TRIALS IN GERMANY:
Winemaking
trials using Flextank vessels are still new in to the German
industry. One trial at the Staatliche Lehr und Versuchsanstalt
für Wein und Obstbau in Weinsberg (State Wine School,
Weinsburg) examined the impact of oxygen on the maturation
of Cabernet Dorsa, a variety known for its deep colour and
high tannin levels.
The
various vessels used included oak barriques, Flextanks and
stainless steel, with and without oak chips. Micro-oxygenation
(MoX) was also applied to wine in some of the stainless
steel tanks. The results are preliminary at this stage,
with the wines still to be bottled and to undergo formal
sensory analysis at that time. However, in-cellar tasting
from each vessel showed that those wines with access to
oxygen (Flextanks, barriques and steel with MoX) showed
a better palate structure than wines without oxygen. This
is consistent with trials in other countries.
WINE
TRIALS IN SWITZERLAND:
The
wine trials that have been carried out in Switzerland tend
to use the smaller volume Flextank vessels, closer to barrel
volume (300L and 600L). One 5 month maturation trial used
a local variety, Gamaret, and compared the following vessels:
-
-
Barrique
(2nd fill Vicard)
-
The
wines were tasted 'in-cellar' (that is, not blind) by 2
winemakers. The Flextank wine was seen as soft, integrated
and structurally 'complete' and the superior wine. The wine
in barriques was similar, except that it was showing slightly
advanced colour and was dominated by oak flavours. The wine
in stainless steel was regarded as 'hard' and not showing
comparable development to the wines stored in Flextanks
and barriques. The wine in Flextank was unambiguously preferred
by both winemakers.
Whilst
the Flextank vessels used in Switzerland are smaller than
those used in the Australian trials, the results in terms
of colour improvement and wine integration are much the
same. Oak staves were not used in the trials in Switzerland,
whereas they were important in Australia. This probably
reflects the different grape type, wine style and marketing
culture in each country.
Although
smaller volume Flextanks were used in the Swiss trials,
the designed oxygen permeation value of 17 mg/litre was
the same as that used in the Australian trials. On the other
hand, the period of maturation used Switzerland was much
less than in Australia. Importantly, winemakers understand
that the driving force for the maturation process is the
inherent permeability of the Flextank vessels.
This
and other trials in Switzerland, South Africa and the US
demonstrate the impacts of maturation of wine in Flextank
vessels to be:
-
-
Tannin
softening and integration
-
Enhanced
complexity of the wine
FERMENTATION & MATURATION TRIALS WITH WHITE WINE
Oxygen
ingress during fermentation and ageing on lees in barrels
is vital to the successful development of white wine styles
such as Chardonnay. Flextank vessels with staves offer an
attractive option to oak vessels, allowing both controlled
oxygen ingress and also manipulation of the oak level by
variation of the number of staves. More staves can be added
or some removed during the maturation process, should the
oak level be regarded as too low or too high, respectively.
In
one Australian trial with a 2008 Chardonnay, the blind tasting
showed a slight preference for the wine in barrel (4 year
old with new oak insert) to the Flextank wine, although
both were allocated to the same final blend. The wine stored
in stainless steel in this trial was allocated to a lower
grade.
A
fermentation trial [again, Australian] with Pinot Gris in
2008 showed that the wine resulting from fermentation in
Flextanks without added staves retained excellent aromatic
characters. The winemakers participating in the tasting
noted that the wine fermented in Flextanks had 'excellent
mouthfeel and showed a high degree of varietal character'.
A
US Sonoma Valley winemaker conducting fermentation and maturation
trials with sauvignon blanc in Flextank vessels placed an
additional purchase order for additional vessels within
3 months, commenting "already the wine in the Flextank's
is superior to barrel...".
These
and other trials, while remaining preliminary, clearly demonstrate
the potential for the application of Flextank vessels to
the fermentation and development of white wines as well
as red wines.
OXYGEN
PERMEATION RATES
The
construction of the Flextank maturation vessels occurs under
highly reproducible conditions that result in well-defined oxygen
permeation rates. The below graph shows oxygen permeation rates
for various wine production technologies, including barrels,
corks and Flextank vessels.

The
data shows that Flextank maturation vessels have oxygen permeabilities
similar to second or third fill barrels. Importantly, a Flextank
vessel with a stated permeability of 17 mg/litre/year will be
exactly that, whereas oak barrels are highly variable in the
permeation rates. Much better control of oxygen ingress can
be achieved with Flextanks. Data
is from the Australian Wine Research Institute together with
measurements obtained by Flextank.
The
defined permeation rates in Flextank maturation vessels
provide winemakers with an option to choose the permeation
rate best suited for a particular wine. As noted above,
the wine trials in Switzerland used Flextanks with a permeability
of 17 mg/litre/year for a short period of time to achieve
the desired level of maturation, whereas the Australian
trials used longer maturation periods with oak staves present.
OTHER
POLYETHYLENE VESSELS

Polyethylene
vessels such as drums and IBC's, have been used for transport
wine and for short term storage for many years. However
it is a common experience that wine stored in these does
not keep well.
In
fact, common
polyethylene containers like drums & IBC's are too oxygen
permeable to mature wine correctly, they:
-
are too thin walled for their volume, i.e. too 'oxidative'
-
have
unsuitable shapes, i.e. have recesses or projections which
trap air
-
are
difficult to clean internally, having small openings
-
are
made from common grades of PE which are incorrect for
maturation
-
often
exhibit a 'burnt wax' taint
On
the other hand, Flextank HDPE Vessels, are engineered to
mature wine by using a correct balance between material
permeability and wall thickness, vessels surface area and
volume.
FOR
FURTHER INFORMATION CONTACT:
Peter
Steer, peter@flextank.com.au,
is Managing Director of Flextank International Ltd. He is
a graduate in oenology from Charles Sturt University and is
a highly regarded winemaker, with more than twenty years winemaking
experience in Australia, USA and France.
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