Whisky is having a moment. Walk into a bar and you will likely be confronted by a bewildering array of choices. There's the Japanese whisky you've heard good things about, Scotch from five different regions - and what's the difference between rye and bourbon, anyway?

"I've been to bars with an amazing selection, but there's so many I don't know what to order," says Charlene Dawes, owner of Hollywood Road whisky den Angel's Share. It's enough to drive someone to drink. But put that glass of Chivas down - there's much more to whisky than the usual brands.

"One-third of our customers are beginners, but somehow they find their way here and talk to the bartender," says Aaron Chan, owner of Club Qing, a cosy Lan Kwai Fong bar that has 150 Japanese whiskies and an array of Scotch. "We always ask questions before we recommend anything."

There are plenty of options. Whisky is one of those rare spirits whose character depends not just on the skill of the distiller but on the alchemy of how and where it is aged. It all starts with a grain. Single malt whisky is made with malted barley, but other varieties use corn, rye, wheat or buckwheat. The grain is steeped in hot water to extract all of the starchy sugars, and the resulting sweet liquid, known as wort, is fermented, producing something similar to beer.

The next step is to distil the brew. Depending on the size and shape of the still, how it is heated and for how long, the same wort can be turned into a remarkably different spirit. At this point, whatever the method of distillation, the resulting product is a clear white liquid, often very high in alcohol. This is what is put into barrels for the final and most important step of the whisky-making process: ageing.

"The cask is an agent of transformation," says Tokyo-based whisky critic Stefan Van Eycken. "Most of the flavours come from the cask - some say as much as 80 per cent."

Oak is best for whisky casks, because it has just the right density to retain liquid while allowing it to breathe, and its chemical mix of tannins and vanillins produce appealing flavours. American and European oak are most commonly used, but some Japanese whiskies are aged in mizunara, a fragrant Japanese white oak used to make incense.

While bourbon must use new oak barrels by law, Scotch and other forms of whisky are often aged in second-hand casks that give them added layers of flavour, aroma and colour. Bourbon, sherry, port: traces of these previous tenants linger even after the cask has been refilled.

Why fans of single malts shouldn’t dismiss blended whiskies

Since casks are permeable, a portion of the whisky inside evaporates every year, something known as the "angel's share". The "angels" take about 2 per cent annually in Scotland, and up to 12 per cent in balmy Taiwan. The warmer the temperature, the faster the whisky ages, absorbing both the characteristics of the cask and what's around it. Whisky aged near the sea is often said to have a briny quality.

Nearly all whisky is blended once it leaves the cask, even single malt, which consists of whisky from different casks produced by the same distillery. Most whisky is a mix of young and old stock, which is blended to achieve a consistent character. If a whisky has an age statement on the bottle - say, 12 years - this refers to the youngest whisky in the blend.

There is one exception: single-cask whisky, which is drawn from just one cask. It is in these rare bottlings that you can really taste how different one whisky can be from the next. It's a good way to discover unexpected flavours: Van Eycken remembers tasting sudachi, a green Japanese citrus fruit, in a 35-year-old single-cask bottling from the now-defunct Karuizawa distillery.

Angel's Share has imported a barrel of Kavalan Solist Sherry Cask whisky from Taiwan, which you can sample at the bar. Whisky @Stables, on the top floor of a Victorian-era stable next to Hullett House Hotel in Tsim Sha Tsui, has its own cask of Mackmyra whisky from Sweden, giving the bar a sweet, woody aroma. "Some of our regulars come back and taste it because it's always changing," says manager Tony Ng.

Whisky makes for good investment as demand for aged and rare single malts grows

Whisky is complex - there are endless numbers of variables that make each one unique. So how do you choose?

Tasting flights are a good start. "Side by side is always the best comparison," Dawes says. Club Qing offers sets that allow you to compare and contrast different whiskies. "We have one set called 'The Harmony of Woods', which is made up of whiskies with a strong wood influence," Chan says. Other sets focus on a single distillery, which highlights the effect of age on the same spirit. Dawes remembers doing a vertical tasting of different aged whiskies from the Macallan. "It was like, oh, so that's what age does," she says.

Food pairing is another way to plunge in At Whisky @Stables, Ng likes to pair the heavily peated Smokehead whisky from Scotland with chocolate-dipped bacon. Ng, a certified whisky ambassador, says the richness of the bacon cuts the smokiness of the whisky, bringing other, fruitier flavours to the foreground.

Dawes says you shouldn't be fooled by branding, labels or tasting notes written by "old Scottish men". Instead, ask the bartender for advice, order a few different whiskies and start your exploration. "There's always going to be a surprise," she says. "So you might as well just try them all."

Japanese whisky – with a wider range of aromas and a thinner, lighter texture – is gaining popularity

This article was originally published in Good Eating