Sunday, June 4, 2017

Management of "Bad Brett": Part I, the conventional approach

Writing about Brettanomyces in Decanter, Linda Murphy stated thusly:
... at best, Brettanomyces can give wine what many believe to be positive attributes that add complexity and depth: earthy flavours of glove leather, smoked meat, bacon fat, tobacco, truffle, clove and other savoury spices. Yet when B(rett) turns bad, it can give wine the offensive stink of barnyard, manure, plasters, wet dog, sweaty horse blanket, mouse droppings and antiseptic.
Remarking about this contrast in character, Clark Smith (postmodern winemaking) stated: "... most connoisseurs have experienced on different occasions both faces of Brett: the sultry, profound earthiness and the repulsive barnyard stench." It is the latter characteristic that is of most concern to winemakers and it is that character that will be the focus of this post.

In a recent Somm Journal article, noted wine writer Dr. Jamie Goode laid out the issues associated with Brettanomyces (Brett) contamination of wines and offered up a number of control measures and fixes to combat same. Clark Smith, in his book postmodern winemaking, takes the conventional view of Brett and Brett management to task and, instead, proposes a schema he calls Integrated Brett Management. I present these competing views in three posts beginning with this one. But first, some background

Brettanomyces bruxellensis falls within the Fermentative class of wine-associated yeasts (the other classes are Basidiomycetous and Ascomycetes), the most dangerous of the wine-spoiler yeasts. According to Woolford, et al., (Genome Survey Sequencing of the Wine Spoilage Yeast Dekkera (Brettanomyces) bruxellensis, Eukaryotic Cell 6(4), April 2007), Brettanomyces bruxellensis is a major microbial cause of wine spoilage worldwide and results in significant economic loss. Brettanomyces is exceptionally dangerous because it has all of the characteristics of Saccharomyces cerevisiae but extends beyond it in that, while slower growing, "it can assimilate a wider variety of carbon choices."  The key characteristics of Brettanomyces bruxellensis are presented in the chart below and its contamination mechanism in the one following.

It was long thought that Brettanomyces contamination was a result of poor hygiene in wineries but contamination persists even in the face of intensive hygiene efforts (Renouf et al., Interactions between Brettanomyces and other yeast species during the initial stages of winemaking, Journal of Applied Microbiology 100 (6), June 2006).  Research seems to indicate that Brettanomyces can enter the winery through sour rot and can then take up residence within the facility and contaminate batches of wine essentially at will. The chart below shows Brett potential contamination sources and pathways. In the case of sour rot grapes, it can be a direct source (that is, mixed in with healthy grapes brought into the cellar) or via bees interacting with sour rot grapes in the field and then bringing Brett into the winery.

According to Clark Smith:
Except in new cellars, Brettanomyces is a ubiquitous organism, a fact of life. Like athlete's foot, one cannot usually hope to eradicate it. Like keeping one's feet dry, control of this organism based on suppressing growth by denying it facile growth conditions is the most realistic solution. Keep in mind that the goal is to facilitate a truce with Brett so a stable condition exists at bottling.
Central to this growth-suppression approach "... is the maintenance of free SO₂ at a level of around 30 ppm at relatively low pH's in order to maximize its effectiveness by increasing the percentage of the free SO₂ that is in the un-ionized molecular form." This approach greatly reduces the number of colonies of Brett that grow on a petri dish but according to Clark, may actually be reducing the culturability rather than actually killing cells.

In his Somm Journal article, Jamie Goode identified a number of actions that can be taken in the fight against Brett. The actions in the left part of the chart below are conventional growth-suppression activities.

Lisa Van de Water (Monitoring microbes during cellaring/bottling, Practical Winery and Vineyard Journal, January/February 2010) recommends testing the wine in the cellar in order to minimize the opportunity for Brett contamination manifesting in the bottle. According to Ms. Van de Water, 100 cells/ml can lead to visible Brett haze in the bottle and the production of small amounts of CO₂. Sensory changes are "profound" with compounds such as 4-EP and 4-EG present manifested by horse sweat and Band Aid odors and a bitter, metallic finish. Bottle variation is common with some bottles showing the clear evidence of "bad Brett" while others show little impact.

Ms. Van de water recommends culturing the wine on media containing 50 ppm of the antibiotic cycloheximide (to inhibit growth of other yeasts) and, if Brettanomyces is present, the culture will manifest white, hemispherical colonies in three to seven days. The culture will, in addition, produce a strong acetic acid smell.

If Brett is determined to exist in the wine at levels between 1 and 50 cells per ml, then we switch to the right side of the chart above and attempt to "fix" the problem. The most common approach has been to pass the wine through a .45µ membrane (this approach can be used both as a control and fix mechanism) but Clark Smith is opposed to this because he feels that filtration disrupts the structure of the wine.

The other wine fixes mentioned by Dr. Goode are identified as key elements of the postmodern toolkit by Clark Smith and so serves as  a bridge between the conventional and postmodern approaches. I will cover them in the next post on the topic.

©Wine -- Mise en abyme

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