Issue link: http://read.dmtmag.com/i/369547
w w w. v w m m e d i a . c o m S e p t - O c t 2 014 | V I N E YA R D & W I N E RY M A N A G E M E N T 6 1 n t i l t h e 1 9 7 0 s , p r e t t y much all fermentations were spontaneous, but now it is common for them to be started by means of inoculating the must with cultured yeasts. These cultured yeasts aren't made in a laboratory, as some advocates of producing more natural wines claim. They are single strains of yeast selected from natural ferments that have gone particularly well. They are then tested, and if they maintain their desirable properties in tri- als, they will be commercially pro- duced, dried and distributed to winemakers by yeast companies. It's not possible to give a reliable figure, but estimates are that today some 80% of all wine is produced with inoculated fermentations. Herein lies one of the great con- troversies of the wine world: Are wines made by spontaneous fer- mentations carried out by "wild" or "indigenous" yeasts more complex than those started by inoculation with single yeast strains? Precisely what are the risks? And is it pos- sible to have true terroir expression when a cultured yeast carries out the fermentation? SPONTANEOUS FERMENTATION The dominant yeasts present on harvested grapes are the so-called "native" or "wild" yeast popula- tions. These are genera such as Rhodotorula, Kloeckera, Hanse- niaspora, Metschnikowia, Can- dida, Pichia and Hansenula. Also present may be potential spoilage spontaneous ferments cause a delay in the onset of vigorous fermentation. This delay could have important flavor and textural impacts on the wine thus produced, quite separately from the character- istics contributed by the diverse set of wild yeasts carrying out the fer- mentation. WILD VERSUS CULTURED There's an ideological divide between those winemakers who advocate natural fermentations and those who choose to use cul- tured yeasts, although many sit somewhere in the middle. At one pole are the likes of Biodynamic guru Nicolas Joly, who maintains that "re-yeasting is absurd." At the other, there are many who share the views of yeast researcher Sakkie Pretorius, who describes the risks involved with wild yeast ferments as "staggering." organisms such as Brettanomy- ces. The main wine yeast is Sac- charomyces cervisiae, and while rarer, still exists in the vineyard. The early stages of uninoculated fermentations are typically domi- nated by Kloeckera, Hanseniaspora and Candida. As the alcohol levels rise a little, these players bow out and others such as Cryptococcus, Kluyveromyces, Metcschnikowia and Pichia step in. It has been esti- mated that in an uninoculated fer- ment, as many as 20-30 strains participate. But as alcohol levels reach 4%–6%, the native species can't cope with the hostile condi- tions and the alcohol-tolerant S. cerevisiae will take things onward from there. So the key difference between natural ferments and those carried out by cultured yeast inoculations is in the earlier stages of fermentation. There are complications, howev- er. Most winemakers will add some sulfur dioxide (SO2) at crushing to reduce the risk of oxidation and also to kill off rogue microbes. This will slant things in favor of S. cere- visiae and the more robust of the native species, eliminating some of the less desirable wild yeasts and spoilage bacteria, which tend to be more sensitive to the microbicidal actions of SO2. Temperature also affects the balance of yeast spe- cies in the fermentation. Cooler temperatures (below 54 F) favor wild yeasts, whereas higher tem- peratures shift things in favor of S. cerevisiae. Aside from the actual proper- ties of the wild yeasts themselves, + Approximately 80% of all wine today is made with inoculated fermentations. + Wild ferments are reported to give more complex wines, albeit at a level of risk that some winemakers find unacceptable. + Cultured non-Saccharomyces yeast (a cultured form of wild yeast) is now commercially available. + A genetically modified yeast strain called ML01 is authorized for use in the United States. AT A GLANCE