Glossary: O

On & Off Trade

On & Off Trade is industry jargon for the types of venues and premises. On-trade refers to on-premise consumption (bars, restaurants, hotels, nightclubs), while Off-trade refers to places that retail spirits for off-premise consumption (supermarkets, off-licences, shops, online-stores).


When it comes to spirits, Oxidation is when oxygen interacts with alcohol. In terms of what’s happening, primary alcohols can be oxidized to form aldehydes and carboxylic acids; secondary alcohols can be oxidized to give ketones. Tertiary alcohols, in contrast, cannot be oxidized without breaking the molecule's C–C bonds.

What does this mean for people who don’t wear three-inch-thick nerd glasses? As the booze reacts with oxygen, its flavours diminish over time. If it's in a well-sealed bottle, the effects of oxidation will be very slow unless you agitate it a lot. 

For Gin, oxidation can cause a loss of limonene compounds (citrus), create a gain of carvone compounds (camphor), and the combination of the two means that the effect is more noticeable as it changes the balance of the botanical recipe. You may find that Whisky, Brandy, Rum all taste a little flatter than when it was brand new although, the swing is less noticeable.


Typically a term that’s connected to Rum, ‘overproof’ can be attributed to spirits that are pretty much any strength above 50% ABV. It’s more directly connected to Rum and Gin due to the spirits’ connection with the Navy.

The term came as a result of the way alcohol was measured. Before the early 1800’s there was no accurate way to measure the strength of a spirit, so Pursers in the British Navy would test the alcoholic strength of the rum they were buying by adding a few drops to some grains of gunpowder. The mixture was lit and if it ignited easily it was “poof” that it was of sufficient strength, if it went up with a bang, it was overproof, it would flame blue (and most likely go boom!).

See Navy Strength

Olla de Barro

Olla de barro is a term for the clay pots used to make Ancestral Mezcal. An ‘olla’ is a ceramic jar used for cooking stews or soups that typically have short wide necks, even wider bellies and are left unglazed.

In Mexico, they are built into a base of either earth or brick (so that it can be heated by a fire underneath it). The pots are filled with the fermented agave must, a catch plate is suspended inside and a copper pan is placed onto top of the Olla filled with cold water. Once heated, vapours rise, recondense off the pan and fall back onto the suspended catch plate and towards the collection vessel. 

The process and science of distillation is the same as traditional pot stills, but the configuration is completely unique, raw, rustic and today is almost exclusive to the production of Ancestral Mezcal.