Many coffee lovers order an iced coffee as the weather warms up. While there's nothing wrong with mixing together a shot or two of espresso with a cup of ice cubes, coffee aficionados now know there are better ways to serve a cold coffee, using techniques that bring out more of the unique characteristics.

"Wine has 200 chemical compounds, coffee has 800 plus," says Nolan Hirte, owner of Aunty Peg's, this new coffee tasting room as well as an on-site bean roastery.

He also owns nearby cafe Proud Mary and is considered a pioneer in the Melbourne coffee scene, a city that's renowned internationally for its exploration of all things caffeinated.

The challenge with serving anything cold is how the range of flavours can be affected. Hirte likens it to drinking red wine. "Put a bottle of red in the fridge, you're not going to understand it properly," he says. "But it still can be enjoyable."

There are technical problems when trying to tease out the aromatic compounds in a cold brew. "When you add hot water to those chemical compounds you start extracting them at different rates," says Hirte, who has been serving cold coffee in different styles for several years.

"But when you add cold water to coffee, those chemical compounds don't respond. The oils don't break down, the fats don't release. There's no heat there to do that so it takes much more time."

There are several ways to brew cold coffee to take advantage of these aromatics, but they all have one factor in common - time. One of the simplest methods is ice drip coffee, sometimes known as cold drip, which is believed to have originated in Japan. The 18 Grams chain of specialist cafes in Hong Kong serves ice drip, where cold water is slowly passed through freshly ground coffee. Managing director John So says it takes about 10 hours to make a batch, but it's worth the wait for the smooth result.

"Because the coffee flavour is extracted very slowly and using ice-cold water, the unwanted sharp acidity you usually catch in a hot cup of coffee turning cold will not be found," says So. "It will be more mellow, fruity and also the floral notes will be much more apparent."

If carefully handled, a batch of ice drip coffee can stay in the fridge for at least a week. At the Coco Espresso small speciality chain, bottles of ice drip coffee with resealable flip-top lids are sold for takeaway convenience.

This week, Coco Espresso also started serving a cold-brew version of pour-over or filter coffee. This technique is even simpler - ground beans are mixed together with water and left to sit for at least 12 hours.

Coco Espresso's founder Johnson Ko, who trained as a barista at his uncle's Australian cafe in North Sydney, says cold brew isn't as strong in flavour as ice drip. It can have low acidity and a chocolate finish.

The most cutting-edge method of delivering a cold brew, however, is via a tap - sometimes called nitro coffee. Hirte has installed some of Australia's first nitro taps. Hirte soaks ground beans in cold water in a stainless-steel tank for about 40 to 50 hours. The oxygen is removed from the tank and at various stages nitrogen and argon are separately introduced to preserve and trap the aromas.

The liquid is put into kegs, with the cold, slightly carbonated coffee being squeezed out of the keg using compressed air via a bladder. The barista then opens the tap and slowly pours a tall glass of brew. It's a much more sophisticated coffee drink; creamy and smooth. (At Aunty Peg's, this on-tap drink is called "Cold Brew".)

As the process is more complicated, time consuming and expensive, nitro coffee isn't as prevalent in Hong Kong. Yet. At 18 Grams, So has just had a nitro machine installed and after some experimentation expects to start selling nitro coffee in June.

The big question is simple, however: is hot coffee better than cold?

"It's a good argument," says Hirte. "In a lot of ways it is. It really depends on what you want to get out of the coffee."

The style of bean can obviously affect the flavour, but no coffee experts emphasise using one particular bean for cold brews. Cold brewing techniques tend to pull out some of the base notes, says Hirte. But it's a struggle to draw out the complexities

Working with hot water is much trickier to get right, however, says Hirte. "The window for hot is very narrow, whereas for cold you get this 24-hour window. With the hot brew you have to nail the technique, the way the hot water hits the coffee, the temperature, the time, the grind size."

Hirte says the grind size is the most crucial component. "It has to be consistent; if you have a small particle and a big particle, they're going to brew at different rates."

Most coffee gurus say that the biggest issue is milk - it introduces a fatty element that can interrupt the delicate flavours of speciality coffees. At Aunty Peg's, the hot and cold brews aren't served with milk. At 18 Grams they also recommend not adding milk or sugar. "If you're looking for something with milk and sugar, we recommend getting an iced latte," says So.

With milky coffee, the process has to be approached differently from the beginning. "The way you roast it, the type of coffee that you buy, the way you extract it," says Hirte. "You have to compromise the terroir to make it work with milk. It doesn't make sense in a lot of ways."