You’ve probably first heard the phrase “whisky on the rocks” from a Hollywood series. It conjures up a classic scene of an agent sipping on his dram while eyeing his target from the corner of his eyes. If a Scot walks into the bar and sees the agent, he’d shake his head in disapproval; then goes to order a dram of whisky straight up—pure as it can be.

So what is whisky on the rocks? And why do the Scots have a distaste for it?

Whisky on the rocks is whisky poured over ice. In Scotland, that would be an insult against their rich heritage in producing the water of life. To the Scots, there are only two ways to order whisky: either neat or with a drop of water. Anything else is a disgrace.

But not for the Americans. Ice is often added to their famous bourbon whisky, much to Pappy Van Winkle’s disappointment. The man believed that whisky should be consumed at full proof (50% ABV) and said, “I see no sense in shipping water all the way around the country.” He also remarked that it’s better to add whisky to water than water to whisky. Quote the Kentucky distiller, “That way you make a poor thing better rather than a fine thing worse.”

It seems, though, that Americans still love their chilled whisky, and the highball—whisky mixed with fizzy drinks, water, and ice—remains a popular dram. The highball, not to be mistaken for her glamorous cocktail sisters, may have gained its name in America, but some believed that the drink was first concocted by the British during a time when the aristocrats would buy soft drinks in large quantities.

Then there’s the Japanese and their infamous Mizuwari style of drinking whisky—a sequel to their highball Izakaya staple that’s influenced by how they consume a traditional Japanese liquor called shochu. The Mizuwari whisky is made by pouring whisky over ice, followed by cold water. A double whammy to the Scots, but the Japanese love it! Walk into any bar down the neon-lit, narrow alleys of Shinjuku’s Golden Gai, and you’ll find a bunch of Japanese and tourists chit-chatting over glasses of Mizuwari whisky alike.

Now, you may be wondering, who’s right and who’s wrong? What makes whisky on the rocks favourable? Good questions. A scientific study on whisky can solve this mystery. Let’s dive right in!

The chemical make-up of whisky

Before we head into how water and ice affect whisky, it’d be good to understand the science behind this complex spirit.

Whisky is made from three main compounds: water (H2O), ethanol, and flavour molecules such as guaiacol (we’ll get to that in a bit). The chemical bond between water and ethanol is what holds the whisky together.

Here is where it gets tricky: water and ethanol generally do not get along, like how water and oil do not mix. The distillers are the peacemakers. They try to balance water and ethanol to form a steady and stable relationship, keeping them together to hold the flavour molecules in place. Each distillery has its method in keeping the peace, and that’s how each bottle of whisky gets its distinct profile.

As water and ethanol naturally dislike each other, the relationship is a fragile one.

What water does to whisky

Adding a drop of water is like dropping a bomb into a tranquil lake. Connoisseurs say that water “opens up” the whisky to a bouquet of flavours. Chemists would say water disrupts the balance, sending the flavour molecules to go this way and that. To a poet sipping his nightcap, water is the homewrecker that splits water and ethanol apart and sets the flavour molecules free.

Not all flavour molecules are alike. There are the hydrophilic molecules—mama’s boys that stick closer to water, and there are the hydrophobic molecules—the rebellious kids that repel water and gladly leave the glass.

You’ve probably guessed it. The so-called additional aromas and flavours didn’t magically materialise with water; they’ve been in the whisky all along. Water releases the hydrophobic molecules, which appear as “new” notes on the nose and palate. For this reason, some prefer to add a splash of water into their whisky.

The shy but smoky guaiacol

Guaiacol gets a special mention because of its attribute to the glorious peaty and smoky note unique to whisky. Pronouncing its name might be a mouthful, but this aromatic oil—a by-product of whiskies aged in charred wooden barrels—is a simple molecule that shuns water and sticks together like glue.

It is commonly present in whisky with 40% ABV, or should we say, in most scotch. Aside from that, whisky that uses partially germinated barley for malt and peat for fuel have slightly more guaiacol in them.

Between ethanol and water, the guaiacol chooses to side with ethanol. No brainer there. That means the higher the proof, the less it’ll mix with water. What more, it has a higher density than H2O and sinks to the bottom of the glass, where it stays hidden like a hermit underwater.

Technically, a straw can force a generous amount of guaiacol up onto the palate, but that may not be a good idea considering how high alcohol content often burns.

An alternative is to add water. A drop is enough to send the guaiacol scrambling up onto the surface and out of the glass. The more water there is, the more this hydrophobic molecule seeks to escape, and the stronger the smoky flavour becomes. The same goes for a few ice cubes, as ice is still H2O.

How much water should I add?

There is no hard rule, but the recommended practice is to start with a drop and top it up from there. For a controlled amount, use a pipette. A lab tool? Yes, as you’ve discovered, whisky is, after all, part science.

A drinking straw works too, but instead of using it to transport the whisky from glass to mouth, use it as a dropper by dipping one end of the straw into a glass of water while covering the other end with your fingertip.

By doing so, the straw draws the water upwards and holds it in due to the shift in atmospheric pressure. Then hover the straw over the glass of whisky and lift your fingertip slowly. If you lift it too quickly, you’ll get a splash instead of a drop.

Don’t like the hassle? Get a pipette. It’ll save you the stress, and nothing should come in your way of enjoying a good dram.

Now, back to the question of how much water to add. What you’re probably asking is how much is too much?

There is no solid answer as each dram, and each type of whisky comes with its complex mix of molecules and reacts differently with water. Booker Noe and other experts say that you can water down a bourbon by 50% without wrecking its core flavours—that’s a 1 to 1 water to whisky ratio. It’s no wonder the Americans dare go crazy with their bourbons and highballs; bourbons are exceptionally robust.

Your best bet is to do a little whisky experiment at home to discover what works best for your palate. Just make sure you write down the exact quantity of whisky and water so you can replicate it in the future. For the more meticulous ones, give Whisky Advocate’s proof calculator a try to find your ideal proof.

Does the type of water matter?

The short answer is yes. Ever wondered why fancy restaurants have a selection of bottled water on their menus? That’s because the minerals in water vary depending on how it’s filtered or distilled.

Soft water aims for as few minerals as possible, while hard water has high mineral content, namely magnesium, calcium, fluoride, chlorine, and bicarbonates. The bicarbonates are nasty and can give off an astringent taste.

A chemical reaction is bound to happen when we mix hard water with whisky. It will, in turn, affect how the whisky tastes. Too much chlorine and you’ll get chlorinated whisky; too much calcium and the whisky goes sour; put in too much sodium—well, salted whisky, anyone?

Distilled water, or purified water, is the best option. It has zero minerals. The next best is to use the same water you drink daily, as you’re accustomed to its taste.

Whisky on the rocks—yes or no? The great debate.

So, adding water to whisky isn’t necessarily a bad thing. What about ice? Since ice is water in solid form, there should be little dispute about adding ice, right? Not quite. Drinking whisky with ice stirs a whole other debate on temperature and the rate at which ice melts.

 

How temperature affects taste

Let’s start with temperature and how it affects our taste buds. As much as we Malaysians love our cold drinks, whisky is best sipped at room temperature unless it’s a scorching hot day. Even the Scots will be able to forgive us for that.

According to science, our taste buds experience more intense flavours in warmer temperatures. The ability to taste these flavours, specifically sweet and bitter profiles, decreases as the temperature drops. That’s not all. An iced drink also mildly numbs the tongue. When a whisky sommelier cautions that ice robs the full experience of drinking whisky, you’d best believe it.

On the flip side, ice does make a dram refreshing, decreases the burn (thanks to the numbing effect), and thickens the spirit’s texture, forming a richer mouthfeel. And what is a whisky cocktail without ice? The last we know, no one likes a lukewarm cocktail.

Whisky and the melting ice—what’s the deal?

Okay, so there are pros and cons to chilled whisky. No biggie there. The real deal-breaker is ice melts. We can control how much water goes into a whisky with a pipette, but there is little control over how melting ice will water the whisky down.

Thankfully, there is a way to appease the purists and please those who want a chilled dram, and that comes down to the size and shape of the ice. The smooth, big round ice you see in movies is not just for aesthetic purposes, but the real thing.

The bigger the ice, the slower it melts; the same goes for spherical shaped ice when compared to an ice cube—the lesser the surface area exposed to the warmth of the spirit, the longer it takes to melt.

Alternatively, there are whisky rocks or stones—reusable soapstone and stainless steel cubes—that chill the whisky without any risk of diluting its flavours.

Some call the whisky rocks a cutting-edge invention of the 21st century, but did you know whisky on the rocks actually traces back to a period when the Scots themselves used stones from the river to chill their whisky?

So, what’s the conclusion?

At the end of the day, whether you choose to drink whisky neat, with water, or on the rocks, it is wholly up to you.

We are not here to dictate how you should drink your dram. We are here to educate so you can make informed choices. There is one thing we do know: you won’t know what your ideal dram is until you have explored what the world of whisky has to offer. So we say, go on, be a whisky scientist and experiment until you have found your perfect match.