I reckon it's high time to post my views, which are somewhat at odds with mainstream enology, concerning this beast and its handling. For the anti-filtration crowd (count me in) this is the central problem facing those who take on the making of serious wine.
The reason is simple. The focus of the GrapeCraft philosophy is the creation and preservation of beneficial macro-molecular structure manifesting in wine as colloidal particles, sometimes nearly as large a microbial cell. Sadly, today’s winemaking practices inhibit the creation of good structure during fermentation and ageing and also disrupt it as part of the bottling process. IBM (Integrated Brettanomyces Management) advocates another approach which preserves and also takes advantage of the benefits of good wine structure.
On one hand, microbial activity when properly husbanded leads to amplification of distinctive terroir characteristics and soulful appeal. One the other hand, wines lacking good structure fail to incorporate these influences properly, and the resulting perception of Brettanomyces as a defect has led to draconian control measures which produce wines of less interest. When these measures become incorporated into a general winery protocol, they harm the development of its wines generally. Paradoxically, these wines not only carry Brett less well but are more susceptible to it, leading to a philosophical snowball effect in exactly the wrong direction. Due to its clever survival strategy, Brett in this environment outlasts other organisms whose competitions normally control it. It becomes a hospital disease, fostered by the very sanitation measures designed to suppress it.
In the recent past, such practices have reached the level of academic dogma, with the consequence that Brettanomyces is now classified outright in many quarters as a spoilage organism. The intrusive aromas of unmanaged Brett include horse sweat, leather, shoe polish, salami, fois gras, truffles, feces, and (Ralph Kunkee’s classic descriptor) “wet dog in a telephone booth.” Nevertheless, only the most zealous of its critics in the press fail to allude to the “good Brett” occasionally acknowledged. In his hilarious article “Attack of the Brett Nerds,” wine importer Kermit Lynch describes this phenomenon and issues a call to reason which has unfortunately been largely ignored.
Why not simply eradicate this organism and make clean, sterile wines of appealing fruit character? Not a simple question to answer. While fresh, unstructured wines such as rieslings are easily stabilized by modern technological tools (sanitation, fermentation with pure yeast strains, refrigeration, pH adjustment, maintenance with inert gas and sulfite preservatives, and sterile bottling), the passages below are intended to explain why these tools are best placed aside or utilized with restraint in the development of fully-evolved, structured wines for which profundity rather than varietal purity is the goal.
The Emergence of Conventional Wine
A technological system developed in Germany shortly after World War II, through the application of technological principles, equipment and materials unavailable prior to the 20th Century, brought into being a new kind of wine unseen in history. Without sterile filtration, the off-dry German wines we regard as “traditional” were impossible to make for commercial sale, because they were unstable in the bottle. Such wines did not therefore exist in commerce in the 6,000 years of truly traditional winemaking, and are more properly called “conventional” wines.
These methods were extremely effective for the production of aromatic white wines whose appeal is based on freshness, varietal purity, crisp acidity and sometimes mineral depth. This style has in the last half century almost entirely eradicated the market presence of traditional white wines, which once shared the mature evolution, oxidative development and microbial complexity which today is the exclusive province of red
wines. Unfortunately, many of the tools and techniques developed for fresh white wines are today used for reds as if there were no fundamental distinction between Riesling and Cabernet.
There persist very distinct sets of aesthetic goals for fresh vs mature wines. Even in today’s conventional reds, attributes such as freshness, varietal simplicity and acidity (often confused with mineral energy) are undesirable traits. Many will question this statement. I do not mean to say that red wine should not have a prominent core of varietal fruit expression, nor that the flat, dull wines so commonly made today from overripe grapes are in any way proper. But the point of most red wine (with exceptions such as nouveau Beaujolais) is to evolve away from its original simple plant characters of berries and herbs into something richer and warmer which touches the soul more profoundly than its original character is able. Its tannins must themselves evolve from a coarse astringency into a rich underlying structure which supports and integrates developing flavors into a coherent single voice.
Conventional winemaking has several disadvantages for vins de garde (wines intended for cellaring). These wines depend on properly formed phenolic colloids, which contain almost all the tannin and red pigment, to provide a refined structure which does not interfere with fruit expression through harsh aggressivity. Products of microbial metabolism, oak influences and vegetal characteristics are also integrated by good structure into a coherent background which is positive rather than interruptive. Modern oxygen-free practices inhibit the development of good structure, and sterile filtration disrupts it.
The Fallacy of Acidity as a Virtue
High acidity exacerbates tannic aggressivity by drawing too much salivary protein into the mouth, thus counteracting the winemaker’s efforts at refinement. Furthermore, low pH inhibits wine development and stabilization, as do sulfites and cool cellars. Palate liveliness is to be prized, but its source is the mineral uptake, still poorly understood, which is characteristic of grapes grown in living soils and is perceived in the back of the mouth, while acid (except acetic acid) is tasted on the front and sides of the tongue.
Winemaking at high pH is thus an essential GrapeCraft skill. Technical details may be found at www.vinovation.com/winemaking_fundamentals/.
Just as the most flavorful and distinctive grapes derive from vineyards employing Integrated Pest Management (IPM) rather than draconian pesticides, so a microbial equilibrium results in more interesting flavor development in the cellar. Like the great unpasteurized cheeses of Europe, wines permitted a natural microbial balance are beyond comparison in richness and profundity to those denied this development. Since many dangers await a wine or cheese so exposed, the transformation must be handled with great skill and attention. Thus the full expression of microbial development is not usually the advisable industrial protocol. Still the range of principles GrapeCraft embodies can be utilized in whole or in part, and most wines will benefit from a carefully thought out program which considers every facet of this system.
Exactly like IPM in the vineyard, IBM seeks in the wine cellar to utilize the natural competitiveness of a complete ecology to maintain the activity of each type of microbe at an acceptable level. It seeks to play out in the cellar any metabolic conversions to which the wine is prone, so that sterile filtration is unnecessary. Any influence inhibitory to this goal should be dialed back to the point where microbial processes achieve completion. Among inhibitors to be considered are alcohol, temperature, sulfites, volatile acidity and pH. Temperature must, for example be held above 60oF for a sufficient period to permit activity to proceed.
Creating a Nutrient Desert
The first steps toward microbial balance should be taken in the vineyard. The goal of these procedures is that a vigorous fermentation can occur which will consume not only all traces of sugar, but also micronutrients so that ensuing secondary growth of Brettanomyces and other organisms is held in check. Paradoxically, the production of a wine poor in nutrients requires a must rich in nutrients to promote healthy yeast action.
The nutrient status of wine in support of secondary microbial growth can be considered to have four aspects: fermentable sugars, nitrogen sources, micronutrients (vitamins and other cofactors) and oxygen. Brettanomyces growth must be suppressed in both of its modes -- fermentative and respiratory.
Our primary ally in suppressing respiratory growth is the wine’s reductive strength. This is because it has been shown that Brettanomyces is able, in the presence of oxygen and ample micronutrients, to utilize ethanol and the secondary amino acid proline, both ubiquitous in wine, as soul sources of carbon and nitrogen sources for growth. Primary fermentation leaves behind these two substances in plentiful amounts; therefore the wine must maintain its ability to consume oxygen in order to protect itself.
Since oxygen is not necessary for fermentative growth, we must depend on primary fermentation to reduce fermentable sugars, and we can assess the risk of Brett fermentation by measuring glucose + fructose via enzymatic testing, which level should be below 1000 mg/L. The winemaker must determine empirically the best method to achieve sugar dryness. Considerations include the choice of commercial yeast inoculum vs wild yeast, avoiding highly elevated sugar in the must, temperature of fermentation and a host of other factors.
Even given good consumption of sugar, toasted wood contributes to wine the fermentable sugar cellobiose which Brett can also utilize. Thus a secondary inhibitory strategy is advisable. Brett is known as a nutritionally fastidious organism, lacking the ability to synthesize for itself many micronutrients. It is therefore beneficial to encourage consumption of these during primary fermentation in order to inhibit Brett in both of its growth modes. To do so, the vineyard conditions to deliver a healthy, nutrient-rich should be mastered. Petiolar nitrogen measurements at bloom can be used to evaluate where deficiencies require fertilization, often in “hot spots” rather than throughout the field. Over-fertilization, which results in excessive vigor and poor ripening, must be avoided through careful topological nutrient management.
In nutrient deficient musts, the author believes that the addition of simple refined chemicals such as diammonium phosphate (DAP) is to be avoided. This chemical is a favorite of modern enologists because it relieves yeast stress and brings about a vigorous, smooth fermentation without sulfide production. However this mode of fermentation is not useful for consuming micronutrients. Since the yeast is fat and happy, it does not need to make enzymes to digest micronutrients as a food source. “If you feed them Twinkies, they won’t eat their oatmeal.” Sulfide production during fermentation is a sign that sulfur-containing micronutrients are being metabolized; the resulting sulfides either blow off or can easily be controlled later by skilled cellar techniques.
Microbial Equilibrium in the Cellar
Except in new cellars, Brettanomyces is a ubiquitous organism, a fact of life. Like athlete’s foot, one usually cannot hope to eradicate it. Like keeping ones feet dry, control of this organism is based on suppressing growth by denying it facile growth conditions. It is important to keep in mind that the goal is to facilitate a truce with Brett so a stable condition exists at bottling. Through nutrient depletion and good reductive strength, we create the best environment possible, and then allow the wine time to play out its inevitable development. Any reductions in alcohol and volatile acidity, any exposure to new wood intended for the wine should occur early, prior to a period (such as a summer) when the wine is held for several months above 60oF.
Final blends should be assembled well in advance to avoid the possibility that a blend may promote additional activity of which its parts were not capable. Different wines can hold back activity for different reasons. In one blend component, low biotin levels may suppress growth. In another wine rich in biotin, folic acid may be lacking. The blend may be less stable than its parts.
An appreciation of the wine’s reductive strength is critical to good cellar management and to the timing of bottling. Reductive strength is a function of phenolic reactivity, mineral composition and oxygenative history. Late harvest reds can have heavy tannin and rich phenolic structure, yet be very low in reductive strength. Sensory properties of reductive wines are a closed aromatic profile and the presence of sulfides. Such wines often have vibrant purplish hues. Low strength wines have open fruitiness resembling tawny port or hazelnut, milk chocolate aromas and often a brick or tawny appearance. Reductive strength can be measured in barrel by introduction of ~1 ppm of dissolved oxygen and following its uptake over days and weeks with a good DO meter. The slope of such a line corresponding to 0.1 ppm in four days is equal to 1 mg of O2 per liter of wine per month, roughly the same rate as a wine is fed through the skin of a typical barrel. Wines possessing less than this rate should be removed from barrel. A good young red wine going into barrel for, say, 15 months should consume oxygen at three or four times this rate.
The third “leg in the stool” of the IBM system is the aromatic integration which takes place in wines of refined, stable structure. Just as in a good bearnaise sauce we cannot perceive distinct aromas of tarragon, fresh onion, vinegar and mint but instead a rich “single voice,” so the aromas of varietal vegativity, oak and microbial activity can be integrated into a good phenolic structure. The finer the colloids in such a structure, the more surface area will be available for aromatic integration. Refinement of tannin colloids requires oxygen, just as in the conching process which converts cocoa powder into chocolate. Skillful use of oxygen to refine structure without encouraging microbial growth is an essential élevage technique. Wines of proper ripeness and good extraction afforded early structural refinement can carry many times the supposed “threshold” of 400 ppb of the Brett metabolic marker 4-ethly-phenol without apparent aromatic expression. Indeed, the nuances added to the flavor impression in the nose and by mouth imparted by a Brett manifestation in these conditions are likely to be quite positive. If such a wine is made without any sulfites, the ensuing complex microbial activity can enhance terroir expression of cherries, wild flowers and garrigue without objectionable intrusion of spoilage characteristics, resulting in wines of greatly enhanced profundity and soulfulness.