What is a sherry cask?

A sherry cask is a more complex category than it sounds. The wood can be American or Spanish. The sherry it held can have been fermented, oxidised or both, and sweet or dry. Two casks described the same way can be made of different wood and have held different wine.

For more than a century Spanish bodegas shipped solera-matured wine to Britain in oak casks, and once emptied those casks were bought by Scottish distillers, who found that wood which had held sherry changed the spirit matured in it. That supply ended. By the 1980s Spanish producers were moving to stainless steel and new regulations required bottling at source, which closed the transport cask trade the industry had relied on.

Scottish distillers had been running cask seasoning trials in Jerez through the 1970s, working out whether casks could be made and filled to order rather than bought once emptied. Jim Swan was travelling to Jerez through the 1980s with blenders and coopers from Scotland, to work out a seasoning programme that could be sustained, and a research delegation went in the spring of 1985. He kept going back to bodegas and cooperages in Spain and Portugal for the rest of his working life.

European oak carries higher levels of extractable phenolic compounds than American white oak, so the two give different results from the same spirit. Reliable methods for telling one from the other in a finished cask did not exist until the early 1990s, which is part of why sherry cask and Spanish oak were used interchangeably for so long.

Misrepresentation is as old as the demand. For as long as sherry casks have been sought after there have been dealers passing off exhausted casks as the real thing. The practice is traceable to Victorian times and warnings about it were still circulating in 2016.