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Wine Glossary: O

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Oak
The oak tree is an important source of wood for barrels. Although other woods, such as cherry, have been (and still are used), oak is the number one choice for wine barrels. See my article on wine and oak for more information.

Oechsle (Germany)
A scale of must weight based on specific gravity. It is vital to assess the must weight in Germany as it determines the Prädikat classification. An Oechsle unit is equal to one unit of specific gravity above 1000. For example, the must of a Mosel with specific gravity of 1090 has an Oechsle of 90 and therefore qualifies as an Auslese. Other measures of must weight include Baumé, Brix and KMW. My article on must weight in my Sweet Wine series gives more information.

Oenology
The science behind winemaking. Popular locations for studying oenology include the University of Bordeaux and University of California Davis.

Oidium
A fungal disease, also known as powdery mildew. Like many vine diseases it thrives in damp conditions. It results in a reduction in quality and yields, but fortunately may be controlled with the application of sulphur, a practice permitted for even organic and biodynamic winemakers.

Old World
In wine-speak the Old World refers to the European nations - France, Germany, Italy, Spain, Austria and so on - with a long history of viticulture. In some instances, particularly in Burgundy and the Mosel, grapes have been grown for the express purpose of making wine for over a thousand years. In many cases we have the local monasteries and noble families to thank for maintaining these great vineyards for centuries, often through difficult times.

Oloroso (Spain)
A style of Sherry - rich and flavoursome, although it may be dry or sweet if Pedro Ximénez has been added. An Oloroso Sherry never developed the coating of flor which protects a Fino Sherry from oxidation and keeps it so pale and dry. The exposure to oxygen causes the wine to darken and develop rich, nutty flavours.

Organic Viticulture
Like any other branch of agriculture, some winemakers wish to rely less on fertilisers, pesticides and other chemicals. Those that meet certain criteria may be labelled as organic. It is often compared to biodynamic viticulture, although this is much more extreme.

Oxidation
The degrading action of oxygen on a wine (or any other substance) is known as oxidation. Hence exposure of the wine to oxygen in the winery is carefully controlled, although not necessarily completely avoided. Exposure to oxygen during racking and ageing in barrel can be of benefit to the wine. Once a bottle of wine has been opened for some time, or if oxygen has seeped past a faulty cork, the oxidised wine will taste off.

Glossary pages: A B C D E F G H I J K L M N O P Q R S T U V W XYZ