Brettanomyces
Brettanomyces
is a common defect in wine, but controversy surrounds the subject. Jamie
Goode sifts the available data and canvasses the views of
world-famous winemakers to determine how widespread the problem is,
and whether brett can ever be a good thing. (Originally published
in Harpers Wine and Spirit Weekly, 18 April 2003, p 42-46)
When Brian Fletcher, chief winemaker at Calatrasi in Sicily,
found out I was writing this feature, he couriered me a bottle of red
wine. Labelled simply as ‘Brettanomyces’, it was a sample from
Puglia that Brian had recently been sent by a producer there. So I
opened it and poured a glass. Immediately, I got a whiff of animal
sheds with some savoury, cheesy character. The palate was similarly
animal-like, with a thin metallic edge. Very rustic. Not undrinkable,
but getting there, and a textbook example of a Brettanomyces-infected
wine.
For those scratching their head wondering what on earth Brettanomyces
is, let me explain. It’s a yeast – that is a unicellular type of
fungus, not a bacterium – that is a common spoilage organism in
winemaking. The goal of this article is to assess how much of a
problem it is, what its effects are and how it can be prevented.
Finally, I’ll look at the controversial issue of whether low levels
of ‘brett’, as it is widely known, can ever be a good thing,
adding complexity to certain sorts of wines.
First, a dull but necessary paragraph to clear up a potential
confusion. The name Dekkera is often used interchangeably with Brettanomyces.
They are actually the same genus (this is the taxonomic group just
above ‘species’), with Dekkera being used for the ascospore-forming
(sporogenous) form of this yeast, and Brettanomyces used for
the non-spore forming type. There are currently five recognized
species of Brettanomyces/Dekkera: B. nanus, B.
bruxellensis, B. anomalus, B. custersianus and B. naardenensis,
with a range of synonyms in common use. Of these, research indicates
that B. bruxellensis is the most relevant to wine.
The microbiology of wine production is a complex business,
and it is beyond the scope of this feature to go into too much detail.
But let me try to give you a feel for the concepts involved. Think of
the plants growing on the slopes up the side of a mountain. At the
bottom there are hundreds of different types, with the pattern of
vegetation changing and progressively decreasing in diversity with
altitude (and a corresponding drop in temperature). It’s a bit like
that with fermenting wine, except that here the variation is temporal
and not spatial -- it is a gradually changing environment for yeasts.
In freshly crushed grape must there are many different yeast species
present, including those normally found on grapes. These rapidly
disappear as fermentation starts and alcohol rises. The environment
becomes more and more inhospitable, and after a while the only
significant yeast species present is Saccharomyces cerevisiae.
As alcoholic fermentation finishes, the S. cerevisiae
population decreases significantly. If by this stage the sugar and
nutrient supplies are exhausted, that’s the end of things and the
wine is stable. But if they aren’t, this leaves the way open for
spoilage bugs to develop; brett is one of the worst culprits here.
What does bretty wine taste and smell like?
Volatile phenols and fatty acids are the key molecules responsible
for the olfactory defects in wines affected by brettanomyces.
According to Peter Godden, of the Australian Wine Research Institute,
‘The anecdotal dogma in this area is that 4-ethyl-phenol, isovaleric
acid and 4-ethyl-guiacol are the key molecules, in order of sensory
importance’. But he adds that he has seen variations in brett
character in different bottles of the same wine. 4-ethyl-phenol is the
most prominent molecule in bretty wines, giving aromas of stables,
barnyards and sweaty saddles (apparently, but I must admit to never
having smelled one). Its presence in wine is an almost certain
indicator of a brett infection, and this is what most diagnostic labs
test for to indicate the presence of brett. 4-ethyl-guiacol is a
little more appealing, known for its smoky, spicy aromas. Isovaleric
acid, a volatile fatty acid, is known for its rancid, horsey aroma,
and as yet there is no analytical technique that picks it out: in gas
chromatography/mass spectrometry (GCMS) another compound elutes at the
same time, which masks it. Godden emphasizes that this is a complex
area of study: ‘There is not much of a relationship between overall
brett character and 4-ethyl-phenol levels, and there are synergistic
effects between the three most important sensory compounds.’
As with other volatile odorants, people differ widely in
their sensitivity to these molecules, and each individual shows a
range of different thresholds (for example, the threshold for
detecting an odorant differs from the threshold for recognition of the
same odorant). Godden suggests that a useful sensory threshold to use
for 4-ethyl-phenol is 420 micrograms/litre. At this concentration and
beyond, a wine will typically be noticeably bretty. Below this
concentration, the character of the wine may be changed but people
won’t, on average, recognize that this is due to 4-ethyl-phenol.
Because the threshold for 4-ethyl-phenol drops when 4-ethyl guiacol is
also present -- and in brett-infected wine they always occur together
in a ratio of about 10:1 -- this threshold is calculated for a 10:1
mixture of 4-ethyl-phenol and 4-ethyl-guiacol.
How common is brett?
The short answer is that brett is highly prevalent, and represents
an increasing problem, even in new world countries such as Australia.
‘We first started raising this as an issue four years ago’, says
Peter Godden of the Australian Wine Research Institute, ‘ and on 1st
July we’re planning to start a major project looking at Brettanomyces’.
As a scientist, he feels that for such an important issue, this
is a relatively under-researched area. ‘There is a lot of
conjecture: anecdotal observations are very important but we have to
be careful with them because they can skew people’s opinions.’
Although brett can and does occur with whites, it is
predominantly a red wine problem. This is because red wines are far
higher in polyphenol content, and generally have a higher pH, both
factors which encourage brett development for reasons which outlined
below.
With rising standards of winemaking worldwide, I was a little
surprised to hear that brett is on the increase. There seem to be two
contributing factors to this rise. First, there is the current trend
for ‘natural’ wines. ‘Minimalist winemaking is a perfect recipe
for bretty wine’, says Godden. ‘It’s probable that the increase
in brett in the 1990s can be traced back to the winemaking fad to stop
adding sulphur at crushing’. Indeed, the most effective way of
preventing brett is to maintain an adequate concentration of free
sulphur dioxide (SO2). Randall Grahm of California’s
Bonny Doon comments, ‘If one is ideologically committed to no
sulfitage at the crusher, this increases one’s chances of brett
dramatically. Likewise, if one uses low or no SO2 in the
elevage of the wines, this greatly increases the risk of brett’.
Preliminary studies by the AWRI show that there is a lot of
genetic variability among Brettanomyces strains. This makes the
correct use of sulphur even more important. If it is added in small,
regular doses, winemakers might unintentionally be selecting for SO2-resistant
strains of brettanomyces, or to put it another way super-brett strains
that are then even harder to eliminate. So timing and magnitude of SO2
additions are important as well as the actual concentrations: the best
way to get rid of brett seems to be large SO2 additions at
strategic intervals.
Second, there is the move towards ‘international’ styles
of red wine, made in an extracted style from super-ripe grapes.
‘These are higher in pH and are richer in polyphenols’, explains
Grahm. pH is important, likely through its role in modulating the
effectiveness of SO2 additions. The higher the pH, the less
effective SO2 is and the more likely that brettanomyces
will grow. Polyphenol content is important because these compounds are
the precursors for the volatile phenols largely responsible for bretty
odours.
A vital risk factor is the presence of residual sugars and
nitrogen sources left over at the end of fermentation. With the
gradual rise in alcohol levels over the last 20 years, the last bit of
sugar commonly isn’t being metabolised by the yeast. Godden suggests
that one solution is to try to keep the wines warm while they are
being pressed. As well as sugar, a nitrogen source is needed for brett
to grow. In fermenting wine, S. cerevisiae uses amino acids as
a nitrogen source. A recent winemaking trend has been to add
diammonium phosphate (DAP) as a supplementary nitrogen source for
yeasts, to reduce the risk of stuck fermentations. However, fewer than
half of musts need actually use this additive, and DAP has been
described as ‘junk food’ for yeasts – they’ll use this in
preference to amino acids, leaving them in the wine as a nitrogen
source that encourages the growth of brett.
Old barrels are frequently touted as the main culprits of
brett, but Randall Grahm adds, ‘The received wisdom about old
barrels, old foudres being the great repository of brett I think is
somewhat mythical and simplistic: dirty barrels, dirty wines, q.e.d.’
Grahm adds that, ‘Since brett is largely ubiquitous, a rampant brett
infection is often more of a function of a large inoculum coming in on
the grapes.
To gauge the extent of the current brett problem, Godden and
his colleagues recently completed a survey of Cabernet Sauvignon wines
in five major regions of Australia. He’s unable to give the actual
results, because these are sensitive, and he thinks that the samples
size, around 170 bottles, isn’t big enough to allow him to draw a
firm conclusion. ‘But if a consumer were to go out and buy a mixed
dozen,’ he told me, ‘several bottles would have more than 425
micrograms/litre 4-ethyl-phenol: if you drink wine regularly, you’ll
have come across a lot of brett.’
Before the 1990s, brett was common in Bordeaux. The wines of
several well known classed growths were well known for their
distinctive ‘stink’. This was almost certainly because of brett
infections, but without the data – and most properties would
understandably be reluctant to own up to this – I can’t name any
names. Since the early 1990s, however, brett has become much rarer,
and this is mainly due to the groundbreaking work of Dr Pascal
Chatonnet. In 1993 Chatonnet carried out a survey of 100 French wines,
and showed that a staggering third of those tested had levels of
volatile phenols above the perception threshold.
The conclusion seems to be that brettanomyces is widespread,
and virtually every barrel of red wine has the potential to go bretty.
Create the right environment for it, and you’ll have a brett
infection. Thus the key objective for winemakers isn’t to create a
sterile winery, which will never happen, but to make sure that their
barrels aren’t a receptive environment for brett to grow in.
Brett, Mourvèdre or terroir? A case study
Brettanomyces is a favoured discussion topic among wine geeks,
who’ll often enter into lengthy discussions about whether a certain
wine is bretty or not. One wine that keeps cropping up in this context
is Château de Beaucastel, the highly regarded Châteauneuf du Pape
estate. To some, the distinctive earthy, slightly animal-like
characteristics of many past vintages of Beaucastel have reflected an
expression of terroir, or even the higher than average Mourvèdre
content of this wine. Others think it’s because of brett infection.
Who is right?
Back in early 1998, Charles Collins, an American wine
collector, became so frustrated with the endless wine geek discussions
about Beaucastel and brett that he decided to find out for himself. He
got hold of some scientific papers on the subject and read up about
the subject. ‘I realised that the presence of the compound
4-ethyl-phenol is a virtually certain indicator of the presence of a
brett infection’, recalls Collins. He contacted a lab who does
testing for 4-ethyl-phenol and sent them some Beaucastel from his
cellar. ‘I opted to test two of the most famous vintages, the 1989
and 1990’, Collins told me. ‘These wines are supposed to represent
what great Beaucastel is all about.’ He prepared the samples for
shipment in sterilized glass 375 ml bottles and used fresh corks to
seal them. The wines were labelled so that the lab had no clue as to
their identity.
The results? According to Collins, ‘they showed
indisputable evidence that significant brett infections occurred in
both the 1989 and 1990 vintages of Beaucastel.’ Microscan and
plating tests showed only small amounts of mostly dead brett cells,
but the 4-ethyl-phenol levels were 897 micrograms/litre for the 1989
and a whopping 3330 micrograms/litre for the 1990. Collins concludes,
‘if you personally like the smell of brett, then none of this should
you dissuade you from buying and cellaring Beaucastel. You should,
however, give up the myth that the odd flavours are due to terroir—they
aren’t.’ I would add that while I’ve detected what I’ve always
assumed, in the absence of data, to be high levels of brett in some
vintages of Beaucastel—the 1991 springs to mind as one of the
brettiest wines I’ve ever encountered—in vintages since the
mid-1990s I haven’t encountered any. But, of course, unlike Collins,
I haven’t done the lab tests that would be needed to verify this.
‘We believe in natural winegrowing and winemaking, and I
must admit that this has led us to have serious debates with
scientists spanning three generations’, responds Beaucastel’s Marc
Perrin. ‘In the mid-1950s, for instance, our grandfather, Jacques
Perrin, decided to stop using chemical pesticides or herbicides on the
vineyard. At that time, when scientists were recommending the use of
such chemicals for productivity or lobby reasons, that seemed crazy
and impossible. Now, it seems that people have changed their mind and
more and more vineyards are turning organic. I could quote many more
examples of opposition between a scientific vision of wine and our
traditional/terroir oriented philosophy of wine, and the subject of Brettanomyces
is just one more’, he explained. ‘There are certainly some Brettanomyces
in every natural wine, because Brettanomyces is not a spoilage
yeast (as many people think) but one of the yeasts that exist in
winemaking. Some grapes, like Mourvèdre, are richer in 4-ethyl-phenol
'precursors' than others and we have a high percentage of these grapes
in our vineyard. Of course, you can kill all natural yeasts, then use
industrial yeast to start the fermentation, saturate the wine with SO2
and then strongly filtrate your wine. There will then be no remaining
yeasts, but also no taste and no typicity. That is the difference
between natural wine and industrial wine, between craftsmanship and
mass-market product.’
Adding complexity?
Beaucastel has been widely acknowledged as one of the world’s
great wines over recent decades. Yet from Collins’ limited sampling
coupled with individual tasters’ experiences, it seems likely that
some of the most successful past vintages of this wines have been
marked by high levels of brett. This leads us to a critical—and
fascinating—question: is brett ever a good thing? In small
quantities, can it have a positive influence on certain styles of red
wines?
If surveys such as those of Chatonnet and Godden are to be
extrapolated across all wines, it is likely that many wines with
above-threshold levels of brett have received critical acclaim and
have been enjoyed by countless consumers. This leads to the conclusion
that while most people won’t enjoy a really stinky wine, low levels
of brett might not be a problem—indeed, a bit of brett might even
add complexity to certain robust styles of wines.
Bob Cartwright, senior winemaker of Leeuwin Estate in Western
Australia’s Margaret River region, acknowledges that ‘a lot of
winemakers like to have some as a complexing character—the question
is how much is too much?’. Randall Grahm is undecided. ‘I suppose
this could theoretically add some complexity to a wine. The problem is
that for now, this is not easily controllable’.
Pascal Chatonnet is opposed. He sees the problem of brett as
a lack of fruit and loss of typicity. ‘If brett is able to grow in
all the red wines of the planet—and this is the case—then all the
wines will have the same odour, which is a pity’.
Godden is another who isn’t keen on the idea. ‘My
view is that if we could eliminate it altogether we would’, but he
stressed that he wouldn't go so far as to say it is always negative.
Godden cites some results from the PhD thesis of Phil Spillman, now
winemaker with Villa Maria in New Zealand. In one study Spillman did
some sensory analyses. The strongest relationship he found was an
inverse correlation between levels of 4-ethyl-phenol and wine
preferences. ‘I’ve not been able to find an Aussie winemaker who
doesn’t find 100 micrograms/litre negative’, adds Godden. ‘In
tests where brett character has been added, it has a severe adverse
effect on the palate. 4-ethyl-guiacol can be interesting and
complexing and doesn’t have the negative palate effect of
4-ethyl-phenol, but with brett infection you get 10 times as much
4-ethyl-phenol than 4-ethyl-guiacol.’
Randall Grahm has an novel suggestion, though: ‘It would be
very interesting if we could isolate a strain of brett that worked in
wine, depleting nutrients but producing very low levels of 4-ethyl
phenol. In this way, one could inoculate one’s wine with brett, much
the same way as one inoculates one’s wine with malolactic bacteria,
thus depleting nutrients and rendering the wine safe from further
microbial degradation.’ Now there’s a project for the
microbiologists. Any takers?
see
also: Brettanomyces
masterclass
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