understanding filterability index: an overview and some ... · some new insights dr paul bowyer,...
TRANSCRIPT
winemaking
80 Grapegrower & Winemaker www.winebiz.com.au November 2014 – Issue 610
Understanding filterability index:an overview and some new insights
Dr Paul Bowyer, BHF Technologies
(Blue H2O Filtration) regional manager,
and Greg Edwards, Vinpac group
technical manager, offer their insights
into the complex topic of filterability
index and how important this
information can be when judgements are made on
wine impact on membranes during sterile filtration
ALTHOUGH it is common for wine packaging facilities
to measure nephelometric turbidity units (NTU) in order to
evaluate wine suitability for particular filtration grades, not
all measure filterability index (FI). Part of the reason for this
lies in the commonly-held falsity that NTU correlates with FI,
but also perhaps because filterability is not a topic currently
taught to winemakers in our education system. NTU is a
measurement of light scattering in a sample, and so provides
an approximation of particulate loading. The measurement of
NTU cannot, however, provide an indication of wine colloidal
status; hence the situation can arise where a very clean wine
with low NTU can still foul filtration media, as was extensively
observed for 2011 South Australian reds. Filterability index
determination is a direct challenge of the wine to be filtered
to the membrane, and so provides an indication of all fouling
components in the sample, whether particulate or colloidal. We
have published previously on this topic and here provide the
most recent developments in our understanding of this rather
complex topic.
FI MEASUREMENTThe measurement of FI is quite straightforward, nevertheless
many laboratories avoid this measurement since, without
appropriate methods and equipment, and it can be cumbersome
and time consuming for laboratory staff. There are several
different methods for determining filterability. Some are quite
complex and some are relatively simple. One universal fact is
that if the method and equipment used are not simple and easy
to work with, this measurement is often neglected and viewed
only as an annoyance.
The method that we advocate is perhaps the simplest. A
sample is delivered to a membrane disc at a constant 2 bar, with
the time recorded to pass 200 and 400mL (or g, in the case of
the BHF automated FI unit). A simple calculation provides the
filterability index as indicated in equation 1:
FI = T400 - 2T200 (1)
Any fouling of the membrane slows the flow of sample,
increasing T400, and so when the formula is applied an
index is generated. Sometimes a constant of 1.67 is applied
but, since it is a constant, it can be omitted. The assay can be
performed manually, but it is far easier to use an automated
Filtration,
Pumps &
Tanks
� ✁ ✂ ✄ ☎ ✁ ✆ ✝ ✞ ✟ ✄ ✂ ✠ ✄ ✡ ✟ ☛ ✡ ☞ ✌ ✁ ✍ ✎ ☞ ✏ ✁ ✑✞ ☞ ✏ ☞ ✏ ✒ ✓ ✟ ✄ ✌ ✁ ✔ ✔ ✁ ✔✝ ✕ ☞ ✂ ☞ ✏ ✖ ✗ ✁ � ✆ ✘ ✙ ✄ ✎ ✏ ✒ ✟ ✖ ✙ ✁ ✔✚ ✗ ✟ ✁ ✖ ✂ ✕ ☞ ✏ ✁ ✠ ✄ ✡ ✟ ✓ ✟ ✄ ✌ ✁ ✔ ✔✝ ✏ ☛ ✄ ✠ ✓ ✖ ✠ ✛ ✖ ✌ ✜ ✔ ✄ ✞ ✕ ✁ ✔ ✔ ✗ ✢ ✖ ✏ ✣ ✤✂ ✄ ✏ ✗ ✢ ✔✥ ✖ ✓ ✖ ✌ ☞ ✗ ☞ ✁ ✔ ✞ ✟ ✄ ✂ ✦ ✧ ✧ ★ ✩ ✧ ✍ ✧ ✧ ✧ ✕ ✪ ✢ ✟GEA Mechanical EquipmentGEA Westfalia Separator Australia Pty Ltd 47 Northgate Drive, Thomastown, Victoria 3074 Phone: 03 8877 9924, Fax: 03 9464 5455 Mobile: 0408 322 524 Email: [email protected], www.gea.com
WIS
A S
UP
PLIE
R OF THE YEAR
AW
AR
DS
WINNER
2014
winemaking
82 Grapegrower & Winemaker www.winebiz.com.au November 2014 – Issue 610
unit. Critically, the membrane discs used for FI determination
should be the same as those membranes used at bottling. This is
sometimes overlooked, but a comparison of relative membrane
performances reveals the importance of this simple point (see
below).
The measurement of FI provides an evaluation of the
fouling that is likely to occur during bottling, however it is
not a replication of the bottling filtration process. Typically,
a sterile bottling task will see the wine pass through tight
lenticular (depth) onto 0.65um membrane pre-filters onto
0.45um final membranes. There are several permutations of
this configuration, but this is the most commonly used. FI
measurement does not replicate this process, since no pre-
filtration is applied before the measurement. Wine destined
for sterile filtration must be within specification (e.g. < 1 NTU)
before it is accepted, in which case minimal loading should be
applied to any of the sequenced filters, yet this is not always
the case. FI measurement is used to detect problem wines,
specifically those that will cause unacceptable loading of
the final membranes, and represents a way of avoiding both
production delays for the packager and elevated filtration
costs for the customer. These wines are typically found to
have low NTU and high FI. We generally advise an FI threshold
of 20 sec.
COLLOIDSThere are two types of colloids found in wine: associative
colloids and macromolecular colloids. Association colloids are
aggregates of small molecules, driven to associate through weak
intermolecular forces such as van der Waal’s forces, hydrogen
bonding and hydrophobic interactions, and are typically
produced by fining processes. Macromolecular colloids are
comprised of one major species, such as polysaccharides,
proteins, mannoproteins, carboxymethylcellulose (CMC) etc.
Generally these compounds possess a molecular charge, and
they can be used to stabilise association colloids, an example
of which would be the addition of gum arabic to stabilise
pigmentation in reds. Colloids can present a problem for
filtration in that, unless the colloid is of sufficient size to be
observed by NTU, it lies latent and undetected in the wine until
it is pushed through a membrane, at which point it can cause
fouling. Since filterability measurement employs the membrane
filtration process, the true filterability nature of a wine sample
can be discerned.
In some cases wines have been ultrafiltered (cross-flow) and
pass FI testing, only to fail a retest within a relatively short time
period. We speculate that examples of this type demonstrate the
impact of associative colloids, which are likely to be disrupted
during ultrafiltration through the application of shear forces,
enabling a pass during FI measurement, but which then
Filterability index measurement is used to detect problem wines, specifi cally those that will cause unacceptable loading of the fi nal membranes, and represents a way of avoiding both production delays for the packager and elevated fi ltration costs for the customer.
GAMAJET TANK AND BARREL CLEANING MACHINES ALLOW YOU TO:
AUS:1800 [email protected]:0800 [email protected]
WINE BARREL CLEANINGHigh and Low Pressures WATER SAVING SOLUTIONSGuns, Reels & Nozzles
Spend 80% less time cleaningUse 75% less water and chemicals during cleaningPreserve the quality and taste of your wineClean your tanks reliably, 100% of the time
TOTAL SPRAYING SOLUTIONS: M-series Tank Washers Spring Rewind Stainless Hose ReelsAccredited nozzles with ;labelling scheme for water use reduction
GAMAJET®
FREEADVICECall us today!
November 2014 – Issue 610 www.winebiz.com.au Grapegrower & Winemaker 83
reassociate in short time to once again provide a mechanism for
fouling membranes.
The impact of macromolecular colloids on FI is more
straightforward, as FI can be measured pre- and post-addition
to determine filterability impact. In some cases a transient
elevation of FI can be observed, such as with the application
of CMC.
FI AND FImOccasionally wines are found that pass FI but present a
differential pressure increase across the membrane during
bottling at a faster than expected rate, so what is going on here?
The basic measurement of FI (Equation 1) gives a filterability
snapshot of the wine up to 400mL, but this has a limitation in
that it is a small measurement (0 – 400mL) and we are seeking
to extrapolate this FI value to the filtration of a large volume of
wine with filters of a much greater surface area. We have found
that by extending the measurement to 600mL and using three
data points, as in Equation 2, to calculate a modified filterability
index (FIm), a better understanding of the wine impact on the
filtration membrane is possible.
FIm = (T600 – T200) – 2(T400 – T200) (2)
In many cases, FI and FIm are very similar values, indicating
that over time the sample is unlikely to have a deleterious effect
on the filtration performance, but on occasion the two values
are sufficiently different in magnitude to raise some suspicions.
It may even be that FI represents a pass value (typically <
20), but FIm does not. Since FIm better reflects membrane
performance over time, perhaps we should be giving this value
proportionately more weight when evaluating the filterability
of a sample.
In Table 1 we can see two data sets for the same wine,
a 2012 Malbec, which has been filtered through different
grades of Becopad. The filtration grades are the same in
each case except for the final grade applied, with 170 being
tighter than 220 (see data in the caption to Table 1). In this
example, the value of the tighter 170 grade as the final
filtration stage becomes obvious when one examines the FI and
FIm data: with tighter final filtration these values are almost
identical, but with a slightly looser grade of final filtration
FIm becomes significantly greater than FI, indicating that
this wine would load the 0.45um membrane to a much
Table 1: FI and FIm data for a 2012 Malbec with different filtration grades applied
in sequence. Becopad 580: Nominal 3.0 - 4.0 um; Becopad 450: Nominal 1.0 -
2.0 um; Becopad 220: Nominal 0.3 - 0.5 um; Becopad 170: Nominal 0.2 - 0.4 um.
FI FIm
2012 Malbec post Becopad 580/450/170 7.80 7.24
2012 Malbec post Becopad 580/450/220 12.0 34.9
Figure 1: A comparison of the FI plots for the wines from Table 1.
winemaking
84 Grapegrower & Winemaker www.winebiz.com.au November 2014 – Issue 610
greater extent than the previous wine, and may cause premature
blockage.
In conjunction with this, there is a strong advantage in using
an automated FI unit, such as the BHF-supplied units at all
Vinpac facilities, in terms of ease of use and laboratory time
allocation, and also in that a real-time plot of the filterability
curve is generated by the software during the measurement.
A sample report is easily generated that can be provided to
the customer to help them understand the filterability status
of their wine. The filterability plot also allows closer scrutiny
of the membrane performance during a filtration run, and this
is not evident when using a manual unit since only a single
numerical value is obtained, constituting only a pass or fail
result. If we examine the plots from the wines used in Table
1, the difference between them becomes immediately obvious
(Figure 1). The influence of the tighter filtration applied through
the Becopad 170 is clearly evident through both the greater
linearity of the plot and the faster flow rate, in addition to
the similarity of the FI (7.80) and FIm (7.24) values. The tailing
evident in the plot for the wine filtered through Becopad 220
indicates higher membrane loading, which is also reflected in
the greater disparity between FI (12.0) and FIm (34.9).
Relative performances of media typesSome laboratories not only use different methods for FI
analysis, but also different membrane discs, disc sizes (25mm
or 47mm) and porosities. For example, some laboratories use
cellulose acetate discs in either 0.45um or 0.65um, yet very
few wine membranes are made of this material. Some facilities
measure FI using nylon membrane discs in either 0.45um or
0.65um, but use polyethersulfone (PES) wine membranes at
bottling. There is no specific standard for FI analysis at this
stage, so it is not possible to transpose data obtained from two
different sources.
The main common element in Australia in terms of sterile
filtration is that 0.45um final membranes are used, and
increasingly PES is gaining prominence over nylon as the
material of choice. The differences between the performances
of nylon and PES membranes are quite significant, in terms
of membrane symmetry, colour binding, FI data obtained,
membrane loading capacity and flow rates. To demonstrate
this, a sample of RO water was analysed, the data for which are
presented in Table 2 and Figure 2. The significantly decreased
334 Hanson RdWingfield 5013Email: [email protected]
Ph: (08) 8244 0011Fax: (08) 8244 0091Sam’s Mobile 0417 864 018
We offer Premium Insulation Services
to wineries Australia wide.
When it comes to insulation services we are the name to trust throughout Australia.
We have the affordable solutions for your winery and offer a range of options including:
www.australiantankinsulation.com.au
Availableall sizes
Wine tank specialists& winery engineers
Fermenter tanks
Rotary fermenters
Variable capacity tanks
Pallet tanks
Storage tanks
Automatic Polisher
IRRIGATOR TANKS
FLAT BOTTOM
VARIABLE CAPACITY
We won’t be beaten on price
Suppliers of:
Filters Cavity wrap Crushers Fittings
Presses Industrial catwalk Valves
Importers & Exporters
Self Discharge Fermenter also available
For more information:
Cosme — AustraliaStainless Steel Fabrications Pty Ltd Wine Tank Specialist
19 Lasscock Road, Griffith NSW 2680 Australia
Ph: +61 02 6964 1155 Fax: +61 02 6964 5336
E-mail: [email protected] Home page: www.cosme.com.au
Membrane material FI FIm Test duration (s)
RO waterNylon 0.45 um 4.6 0.6 178
PES 0.45 um 0.0 0.0 59
Table 2: FI and FIm data for RO water passing through nylon and Parker-
domnick hunter PES 0.45 um discs.
Figure 2: A comparison of the FI plots for RO water using nylon 0.45 um and
a Parker-domnick hunter PES 0.45 um disc. Both membranes generate quite
linear plots (in this example) but exhibit different flow rates and FI data.
November 2014 – Issue 610 www.winebiz.com.au Grapegrower & Winemaker 85
flow rate of the nylon disc is a result of both the membrane
composition and symmetry.
In a similar way, cellulose acetate (or ‘ester’) discs are
commonplace in laboratories, and are often used for cell counts
on growth media, although their use for generating FI data
is debatable given that most wine membranes are either PES
or nylon. In Table 3 and Figure 3 we can see data for a wine
analysed using 0.65um cellulose acetate discs (as was laboratory
practice at the site in question) and PES 0.45um discs (which
was the membrane type in the bottling hall filters). The 0.65um
cellulose acetate discs, having the greater porosity, allow a
greater flow rate than the 0.45um PES discs, and even though
the FI data obtained are similar the FIm data are quite different.
The discrepancy is perhaps more obvious in the FI plots
depicted in Figure 3.
CONCLUSIONThere is, as yet, no specific standard for filterability analysis
in terms of method applied, membrane disc size and membrane
composition. These parameters can influence filterability
analysis outcomes, and this should be borne in mind before
seeking to draw comparisons between data sets. Our advice is
to use 25mm membrane discs for filterability analysis that are
identical to the final wine membranes in terms of porosity and
composition. In this way filterability information of the greatest
value can be used to make judgements regarding wine impact
on membranes during sterile filtration.
For more information, contact:
Paul Bowyer
P: 61 3 9564 7029
REFERENCESBowyer, P. K., Edwards, G. and Eyre, A. (2012) NTU vs wine filterability index – what does it mean for you? The Australian and New Zealand Grapegrower and Winemaker, October issue (585), 76-80.
Bowyer, P. K., Edwards, G. and Eyre, A. (2013) Wine filtration and filterability – a review and what’s new. The Australian and New Zealand Grapegrower and Winemaker, October issue (599), 74-79.
Bowyer, P. K. (2003) Molecular polarity – it’s behind more than you think, The Australian
and New Zealand Grapegrower and Winemaker, November issue, 89-91.
Table 3: FI and FIm data for a 2013 Shiraz analysed using 0.65 um cellulose
acetate and 0.45 um Parker-domnick hunter PES discs. Note the large
difference in FI and FIm data for the cellulose acetate disc.
Figure 3: A comparison of the FI plots for a 2013 Shiraz using a cellulose
acetate 0.65 um disc and a Parker-domnick hunter PES 0.45 um disc.
The flux characteristics here are quite different, with the cellulose acetate
membrane leading to significant tailing, which in turn elevates FIm.
Membrane material FI FIm Test duration (s)
2013 ShirazCellulose acetate 0.65 um 4.3 27.2 104
PES 0.45 um 4.7 2.4 131