We begin with some baseline definitions. An odor is a volatile compound, or combination of volatile compounds, that stimulates the olfactory organ to register a smell. The odor threshold of a compound is the lowest concentration at which its smell can be detected. The perception threshold is the minimum detectable concentration for 50% of a group of tasters while the recognition threshold is the minimum concentration of that compound necessary for identification of the odor.
If we relate the foregoing to wine, quality wine can be characterized as having complex associations of aroma compounds that exceed the odor threshold; and, for a subset of tasters, exceed the recognition threshold. But what are the sources of these odor? The figure below shows the sources of wine odors.
As the figure shows, wine odors are a sum of the odors from the grape, maceration, yeasts, alcoholic fermentation, malolactic fermentation, and aging. The Wine Institute characterizes these odors as shown in the table below.
Over the course of the next few posts I will detail the elements that ensure the production of quality wine grapes, characterize the sources of wine odor, and, finally, show how the interaction of these odor compounds aid in the perception of a quality wine.
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