How to Make an Iced Latte: Ratio, Ice and Why Cold Coffee Needs More Coffee

An iced latte is espresso and cold milk poured over ice. To make one, fill a 350–400 ml glass about two-thirds full of ice, add about 150 ml of cold milk, and pour a double espresso over the top — then stir, or drink it as it marbles.

That is the whole recipe, and it works. What makes the difference between a good iced latte and a watery, faintly coffee-flavoured glass of milk is understanding what cold does to coffee, and what the ice actually does to the drink.

The recipe

1. Fill the glass about two-thirds full of ice.
2. Pour in the cold milk.
3. Pull a double espresso. If you want the drink sweet, stir sugar or syrup into the hot shot now, while it will still dissolve.
4. Pour the espresso slowly over the top. It will settle on the milk, then marble down through it.
5. Stir, or sip it layered.

The quantities follow the advice of Arla Foods' barista guide, which suggests starting with the same coffee and milk as a hot latte and simply pouring them over ice: milk first, espresso second, so the coffee marbles through the glass. The guide notes that iced lattes have no traditional size and end up much larger than hot ones, because the ice takes up so much room.

The marbling has a physical cause. Espresso is less dense than milk — the starting point of a 2017 Princeton study of layered lattes — so a shot poured onto cold milk tends to sit on top before it mixes. The macchiato guide explains the layers in more detail.

How much the ice really dilutes it

Many people use less ice to avoid a watery drink. The physics says that only helps up to a point.

Ice melts by absorbing heat — 334 joules for every gram, with no change in temperature. The heat it absorbs comes from the espresso and milk. Run the numbers for a double shot that lands at about 70 °C:

• Cooling 36 g of espresso to 0 °C releases about 36 × 4.18 × 70 ≈ 10.5 kJ, enough to melt about 31 g of ice.
• Cooling 150 ml of milk from fridge temperature, about 4 °C, to 0 °C releases about 2.5 kJ, enough for roughly 8 g more.

So even if everything were chilled to freezing, the ice would add only about 40 g of water — about a fifth of the drink. And that amount is set by the heat that has to come out, not by how much ice is in the glass. Once there is enough ice to absorb that heat, more ice does not add more water; it just keeps the drink colder for longer as the room warms it. Too little ice is the real risk: it all melts, and you are left with a cool, slightly diluted latte rather than a cold one.

Two practical consequences follow. Large cubes are better than crushed ice, because their smaller surface area means they melt more slowly as the drink sits. And if you want less dilution, cool the espresso before it meets the ice — in a chilled metal jug, or a cup standing in iced water — rather than starving the glass of ice.

Why an iced latte needs more coffee

The same shot tastes weaker cold than hot, for two reasons.

Cold coffee releases less aroma. In a 2017 study in Food Chemistry, researchers served the same coffee at six temperatures from 31 °C to 62 °C and measured both what tasters perceived and which aroma compounds escaped from the cup. Release of volatile compounds rose steeply above 40 °C, and the hotter coffees had more overall intensity and more roasted and bitter notes. An iced latte sits far below even the coolest of those samples, so far less of the coffee's aroma reaches your nose.

Cold drinks taste less sweet. A 2005 study in Nature found that TRPM5, a channel in taste cells involved in sweet taste, responds much more strongly as temperature rises towards body heat. At fridge temperature, the same sugar — including the lactose in milk — registers more weakly.

Together, these explain why an iced latte made with a single shot tastes like cold milk, and why iced drinks are so often sweetened. The fix is more coffee, not less ice: use a double as the minimum and a triple in a large glass, or cut the milk back.

Sweetening it

Sugar dissolves slowly in cold liquid, so granulated sugar stirred into an iced latte tends to sink and sit undissolved at the bottom of the glass. Dissolve it in the hot espresso before the shot meets the ice, or use a syrup, which is already dissolved. A simple syrup of equal weights of sugar and water is easy to keep in the fridge.

Caffeine and calories

Milk and ice add no caffeine. At the USDA's average of 212 mg per 100 g of restaurant espresso, a 36 g double carries about 76 mg, and a triple about 115 mg. The caffeine guide compares other drinks.

With 150 ml of whole milk at the USDA's 61 kcal per 100 g, an unsweetened iced latte comes to about 95 kcal, nearly all of it from the milk. Each teaspoon of sugar adds about 16 kcal.

Variations

• Iced mocha. Stir a tablespoon of cocoa and a couple of teaspoons of sugar into the hot espresso to make a paste before pouring it over the milk and ice. The mocha guide explains why the paste matters.
• Iced caramel macchiato. Vanilla syrup and milk over ice, espresso on top and a caramel drizzle — see the caramel macchiato guide.
• Iced americano. Leave out the milk and use cold water; the americano guide has the ratio.
• Without an espresso machine. Use 60–80 ml of strong moka pot coffee, or cold brew concentrate, which needs no cooling at all.

For black iced coffee brewed hot straight onto ice, see the iced coffee guide, and for the hot original, the latte guide.