The aromatic compounds are, of course, the magnet for the technique. Few of the key volatiles in wine aroma are found fully formed in grape skins or juice; most require fermentation to develop. But monoterpenes — linalool, geraniol — and grassy methoxypyrazines do exist in their native states and can be powerful ingredients in the aromas of a finished wine. Both of these classes of compounds are found in high concentrations in the skins of certain grape varieties.