Cellar Dweller
Oxygen and wine: Sleeping with the enemy
Nurturing a wine from vineyard to bottle is an interesting journey, seemingly a straightforward trip, but strewn with serendipitous paths along the way.
Gary Strachan
he straight and narrow path is the conversion of sugar to alcohol. Some refer to this as the Lavoisier Equation. It is the overall summary of fermentation: Glucose is converted to ethanol and carbon dioxide plus heat. The process is mediated through the yeast Saccharomyces cerervisiae, literally a sugar-eating fungus named after Ceres, a Roman goddess with several hats: agriculture, grain crops, fertility, and motherly relationships (according to Wikipedia). There are many other closely-related species such as S. bayanus, S. uvarum, S. saki, S. carlsbergensis, etc. Yeast species are so closely related that many can interbreed. Thus the line between one species and another is rather fuzzy. I’ve made bread with wine yeast and fermented wine with bread yeast. The differences between them are mainly a matter of their having been selected for the properties of individual strains, much as the clones of a single grape variety are selected and then propagated vegetatively.
T
The various strains of yeast comprise the most economically important group of microorganisms in the world because of an interesting phenomenon. They are facultative
28 British Columbia FRUIT GROWER • Winter 2011-12
anaerobes. In the presence of air, they grow with essentially the same biochemistry as higher plants and animals, but in the absence of air they continue to grow but release ethanol as the end product of sugar consumption. If air is restored, they can consume alcohol and metabolize it further to yeast biomass, energy, and carbon dioxide. Many other yeast species can ferment sugar but none is as resistant to alcohol as the Saccharomyces species.
There is another interesting
phenomenon known as the Crabtree Effect that occurs in
Saccharomyces species.
n the presence of high concentrations of sugar, glucose is fermented to alcohol, even in the presence of air. When we consider these factors in concert we gain insight into the stages of the fermentation process.
Antoine-Laurent Lavoisier, an 18th century French nobleman, is often called the father of modern chemistry. He co-discovered, recognized, and named oxygen as well as hydrogen, and, among other things, helped introduce the metric system.
For example, at the beginning of fermentation, must is generally cold, and is close to saturated with oxygen from having come through a destemmer and possibly a press. Oxygen is consumed by the yeast but sugar is converted to alcohol because
Since the beginning of BC Wines, Flory Bosa has devoted her talents to ensuring the best supplies for her customers. Flory joined the industry in 1989, and worked with the BC Amateur Winemaker Association. Today she serves the needs of small, medium and large wineries. If you want to get the best from your grapes, come to Bosa. Where wine, and winemakers, matter.
6908 Palm Avenue Burnaby BC 6044739463
186655GRAPE (47273)
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