ALTERNATIVE REALITIES III
LET’S BE CLEAR
Kieselguhr has been the industry standard seemingly forever for filtering particles and
ensuring beer clarity. Today there are challengers taking on the established practice,
namely crossflow filtration. Is what’s new on offer actually better, and how great are the
actual challenges in DE use, wonders UC Davis professor Charlie Bamforth
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ALTERNATIVE REALITIES III
O
ne careless conversation was all it
took to dull our beer.
For reasons lost in the mists
of time, the lady in the QA team
decided to suggest to the most strident of the
union conveners that handling kieselguhr was
not a good thing from a health perspective.
Totally ignoring the fact that the brewery had
the latest in powder handling technology (one
of the more efficient of systems in an otherwise depressingly degenerate operation), the
unions straightway declared that henceforth
they would never touch the stuff. And so we
brought in the perlite.
It is a simple and undeniable fact that
kieselguhr (or diatomaceous earth, DE, as most
folks refer to it these days) is actually a darned
good filter aid. No matter how you look at it (the
proof is indeed in the looking) perlite performs
less well. And so the result in the brewery was
a product that was dull. Sure, it was not overtly
hazy. It was simply less than brilliantly bright as
judged on a light box.
Perhaps if we had used a secondary filter of
some sort to back up the perlite on the plateand-frame we would have achieved ideal clarity.
But we didn’t. Not a sheet filter. Not a cartridge
filter. That would have meant additional investment – and the company were certainly not going
to throw more money at a brewery in terminal
distress due to the cancer of the militants.
DE will trap all bar the tiniest particles (less
than 0.4-0.6 µm). Perlite, though, will allow proportions of particles (right the way up to 16 µm
and especially up to 4-5 µm) to come through.
Hence our problem.
Another way
Despite the excellence of DE, there have long
been moves afoot to find ways and means of
avoiding using it. There are at least three arguments made to justify this.
• The first concerns the respiratory issues but,
as we have said, properly configured pneumatic handling systems make this a relatively
minor concern.
• The second is: “what do we do when the DE
runs out?” All I can say is that the last time
I drove on the Lompoc Road in Southern
California there were some pretty impressive mountainsides that comprise kieselguhr.
I really can’t see any genuine likelihood of an
early shortfall.
• The third concerns the disposal of the used
filter aid. Perhaps this is the most challenging
of the three, but not entirely insurmountable. DE
can be incorporated into building materials. And
it can certainly be regenerated with caustic,
furnacing and/or hydrocyclone processing.
Yet it cannot be denied that there is a logic in
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•
not generating a co-product in any process. (How
much more convenient it would be, for example,
if there was no such thing as spent grains!). And
so the inevitable search for a filtration system
that does not need filter powder.
To crossflow filtration
The crossflow-for-beer adventure started at
least 25 years ago. For the longest time the concern was one of achieving sufficient throughput
one meter long and with an internal diameter
of 1.5mm. Each module represents a filtration area of perhaps ten square metres. The
beer is pumped through the modules – with a
not inconsiderable energy demand, especially
when considered alongside the increased
need to cool to counter the heating induced
in the pumping.
Another approach is to place a centrifuge
ahead of the filter, thereby reducing the solids
“It is a simple and undeniable fact that kieselguhr
(or diatomaceous earth, DE, as most folks refer to it
these days) is actually a darned good filter aid”
rates. As brewers have known since time immemorial, beer needs to be filtered cold.
(I still cringe to hear “cold filtered” for the
advertising of certain non-pasteurised beers: all
self-respecting brewers filter their beer cold.)
At these low temperatures the enhanced viscosity leads to reduced flow rates. It’s okay for
less sophisticated beverages (I would say) such
as wine and cider which can be filtered warmer.
Hence the technique has long since been used
to clarify these fluids. For beer the flux challenge
has had to be overcome.
This was one hurdle: the second was one of
component loss on the membranes. This had two
implications. First, a fouling and hence obstruction of membranes, in itself restricting liquid
flow. Second, the removal of substances that
are somewhat important for beer quality, notably
bitter acids and foaming proteins.
The difficulty is actually less than it is in simple surface filtration. In this the beer is passed
directly (“head-on”) through the membrane. The
potential for clogging of the pores is immense.
In crossflow systems the beer flows at
right angles to the membrane so there is a
continual scouring of the surface, preventing
particle build up.
However, there is still some fouling of
the membrane by adsorption. Developments
in membrane composition (membranes are
typically ceramic or polymeric, e.g. polyethersulphone) have reduced the magnitude of the
problem, and there are additional opportunities
for reversing the effect. These include “back
pulsing” in which the clarified beer is forced in
the reverse direction to lift blockage materials
out of the pores. Alternatively the membranes
can be vibrated and the particles literally
shaken into submission.
A typical crossflow system would consist
of modules of tubular membranes perhaps
Brewers’ Guardian, July/August 2010
loading onto the membrane. Indeed, it has even
been suggested that a centrifuge might be used
ahead of a surface or depth filter such as a sheet
or a pulp filter. Centrifuges aren’t cheap, though.
Assessing
clarity
Not long after I joined Bass I was asked
to write a recommendation of the angle
at which we should assess haze: whether
the haze meter should be of the traditional right-angle scatter variety, or one
of the newer ones that measured light
deflected at a “forward” angle, such that
“invisible” hazes were not detected. All the
breweries in the group agreed except for
one, Glasgow, whose letter to my boss
Stuart Molzahn read: “We don’t necessarily
disagree with everything in Dr Bamforth’s
memorandum. For example, he has spelled
his name correctly.”
No matter: I still maintain that the best way
to assess beer brilliance is to put the beer
on a shelf before a light box that features a
black line as shown in the diagram. If upon
looking through the beer the edges of the
line are crisp and distinct then the beer is
bright. If the edges are even slightly blurred
then the beer is dull. This is what we had at
our brewery.
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ALTERNATIVE REALITIES III
So what else?
Filtration systems: beer quality primary concern, ultimate goal
The capital investment considerations for the
entire filtration system for breweries producing
less than, say, 2.5 million hectolitres of beer per
annum, might be a tad scary.
Unlike a powder filter where the filter contents (the DE or perlite) are dumped, the membranes are repeatedly re-used in a cross-flow
filter, thus the need for consideration of the
preferred cleaning regime, which apart from
caustic and/or acid might also involve oxidative
and enzyme rinses.
There are clear intuitive advantages of
crossflow filtration, not least the prospects
for more ready automation than a system that
depends, for example, on the slurrying of filter
acid. Indeed, it has even been suggested that
some systems could yield sterile beer, with
no subsequent need for either pasteurisation
or sterile filtration. It has also been pointed
out that, when compared to a powder-based
system, crossflow makes for less water consumption, less beer losses, less carbon dioxide
consumption, less risk of metal ion pick up and
reduced operating expenditure.
At the end of the day it comes down
almost to a matter of “suck it and see”. At
one extreme we might say that no two beers
are the same. They will differ greatly in their
content of particles – some tending to contain
“There are clear intuitive advantages of crossflow
filtration, not least the prospects for more ready
automation than a system that depends,
for example, on the slurrying of filter acid”
relatively large levels of bigger particles such
as yeast, others containing disproportionate
amounts of much smaller particles. And so
there is no better bet than to assess the
filtration performance in the various systems
(classic powder versus cross flow) in respect
of fluxes, propensity to fouling and quality
of the finished beer. Only then can a proper
economic comparison be made.
How dull was that?
The much loved Preston Besford had the
microscope set up on the lab bench.
“I say, old boy” he said, in his typically refined
and jovial tones; “what do you suppose we
have here?”
I peered through the lens. Unmistakably it was
rod-shaped bacteria. In the immortal words of
John Cleese (a la parrot) they were ex-bacteria;
no longer of this world; they had ceased to
be. But, dead or not, they were still a blessed
nuisance, for this was the stuff that had evaded
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And this evaluation needs to include some
of the novel filter aids that are coming into the
market place. These include cellulose fibres, rice
hulls, and synthetic polymer materials that may
incorporate PVPP, thereby allowing filtration and
stabilization in one fell swoop.
Perhaps the most publicized of these is an
extruded blend of 70% polystyrene and 30%
PVPP, marketed on the basis of it being utilisable on the existing filters that a brewer might
presently be employing for DE-based filtration.
Arguably the biggest selling point is that the
material is pretty much entirely regenerable,
by successive washes with hot caustic and
enzymes that nibble away the sticky residue that
owes itself to yeast cell wall glucans.
The problem is that the regeneration cycle
takes 5-6 hours, not particularly desirable for
those who don’t want their filter down for such
a protracted period. The solution of course is a
parallel operation, with one filter functioning and
the other in regeneration mode, though that of
course rather changes the economics.
And what of variations in the clarity of the in
the perlite. The cause was malt of less than
pristine cleanliness coupled to the less than
necessary filtration. We were sworn to secrecy
– the powers-that-be being embarrassed that
we could possibly have such an issue.
Ah! Two years later the folks from Guinness
reported a similar clarity problem in an EBC
presentation – and several years earlier there
had been a Labatt paper on haze that spoke
about teichoic acid, a polymer unique to bacterial cell walls.
stream? Changes in the solids loading approaching
the filter would (with a DE system) be responded
to by adjustment to the amount of filter aid dosed.
But with a material that simultaneously clarifies
and stabilises there will be an accompanying fluctuation in the amount of PVPP introduced.
In conclusion
As for most other elements of a brewery
operation, there are plenty of schools of thought
when it comes to filtration (and stabilisation)
operations. And dare I say that the primary
consideration is the quality of the finished beer in
respect of its appearance, flavour and stability.
Only then chew on the costs. Any changes in
approach need to be considered carefully and
evaluated extensively. No knee-jerk reactions,
please, that speak to dullness in every manifestation of the term.
Charlie Bamforth is the Anheuser-Busch
endowed professor of malting & brewing
science at the University of California, Davis.
Correspondence is welcome via email:
[email protected]
© Advantage Publishing Ltd
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