| Oak chips |
| Chips of wood placed in used barrels or stainless steel tanks, used increasingly, as are oak staves to impart wood flavours. Frowned on by some purists still, the 'additives' approximate those of a new barrel and are far cheaper. |
| Oaky |
| Displaying exaggerated oak/wood aromas and flavours (vanilla, spice, char, woodsmoke etc). Young wines can outgrow oakiness, older ones less readily. |
| Oenologist |
| One who studies wine and winemaking. |
| Oenology |
| The study of wine and winemaking. |
| Oidium |
| One of several fungi that can cause severe damage to grape crops; also called powdery mildew. |
| Oxidation |
| Change (usually for the worse) due to exposure to air, in whites often producing dark yellow or yellowish colour (called maderisation). Controlled aeration is used to introduce acceptable and desirable development in wine. |
