Naturally occurring enzymes (phenol oxidases) that can trigger the oxidation of phenolic compounds on contact with oxygen and thus contribute to the undesirable browning of the grape must. The grape's own species tyrosinase (a copper-containing enzyme that catalyses the oxidation of phenols to quinones ) is largely removed after pressing when the must...
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The glossary is a monumental achievement and one of the most important contributions to wine knowledge. Of all the encyclopaedias I use on the subject of wine, it is by far the most important. That was the case ten years ago and it hasn't changed since.
Andreas Essl
Autor, Modena