If I were to ask you “What is the most important of all cocktail ingredients?”  You might answer gin, or whiskey.  Or perhaps sugar or lemon juice.  Or even Bitters.  But the real answer is ice.

Without ice we can’t make cocktails.  It really is as simple as that.  So it should be no surprise that the first great cocktail era towards the end of the 19th century coincided with the development of refrigeration technology.  Before the development of chilling technology, access to ice outside of winter was limited to the extremely wealthy.

There are stories of how ice was transported from the Himalayas to the court of the Mughal Emperor in Agra.  So that the Emperor could enjoy an iced beverage during the height of the Indian summer.  And every British manor house in the Victorian era included an ice house, built into the north facing slope of a hill.  Blocks of ice would be frozen and then stored here, hopefully lasting throughout the year without completely melting.

Ice

Ice

But such options were only available to a fraction of a percentage point of any society.  As such, ice (outside of winter time) remained a luxury item until quite recently in historical terms.  But over the past 150 years it slowly became ubiquitous.  And with it being increasingly commonplace, more and more people could experiment with it.  And the rest is cocktail history.

The Trade Off of Ice

As discussed in the Mixing Theory post, cocktails generally taste best when they are cold.  But unlike say a bottle of beer, a cocktail is not a pre-mixed drink which can be left in the fridge to chill.  At least, not in the kind of quantity to be useful for a bar.  Though when making drinks for a house party of limited size, you do have this option.  And though I am aware of the recent trend of pre-mixed bottled “cocktails”, I have yet to try any of these that wasn’t…shit.  And since my aim is to tutor you in making good to great tasting drinks, I’m happy to ignore them.

So, the application of ice to a liquid is the primary method bartenders have of chilling cocktails.  But as noted in the Mixing Theory post, this is always going to result in a trade off.  As ice heats up it melts into water, resulting in the dilution of a cocktail.  This trade off between chilling and dilution is absolutely central to the making of cocktails, and a proper understanding of it is key.

Of course in order to understand it you don’t need to understand the precise physics behind it.  While I could lecture you on the specific heat capacity of both ice and water and the thermodynamics involved in chilling it’s not strictly necessary.  We are interested in a craftsman’s level of precision here and not a scientist’s.

Equilibrium of Temperature

Having said that, there is still important stuff we need to understand.

The first is that ice is merely water which has become cold enough to turn into a solid.  As we all know, the temperature at which water freezes is 0° C.  So when ice is exposed to environmental temperatures greater than 0° C, it begins to melt.  The rate at which it melts is naturally dependent on the temperature of the environment into which it is placed.  So ice placed into a glass at room temperature will take a lot longer to melt than ice placed into an oven.

However, we should remember that only pure water freezes at 0° C.  Water which is not perfectly pure may have a significantly lower freezing temperature.  Especially when it contains alcohol, as pure ethanol freezes at -114.1° C.  Most spirits, at ~40% abv, freeze at around -30° C, which is how we can keep vodka in our freezer without incident.  So expect the freezing point of a cocktail to be a sub-zero temperature.

When you place cubes of ice into a liquid two important things happen.

Ice

Ice melts

The first is heat exchange.  Simply put, the ice draws heat out of the liquid and into itself, heating up in the process.  However, ice can only draw heat out of a liquid providing that there is a difference in temperature between ice and liquid.  Over time the temperature of the ice and the liquid will approach each other and then equalize.  At this point we say that an Equilibrium of Temperature has been reached.  Once reached, neither ice nor liquid can get any colder.  Any further change in temperature is the result of this liquid-ice mixture interacting with the environment in which it is placed.

The second is that as the temperature of ice increases it melts.  This results in dilution of the liquid with pure water.  Note that this melting occurs on the surface level of a piece of ice.  Because this is where the temperature exchange occurs.

Implications

There are several implications of this concept of practical importance to bartenders.

Sidecar

Sidecar

The first is that once this Equilibrium of Temperature is reached, the chilling of a cocktail ceases.  It will not get any colder.  No matter how long you continue to stir or shake it.  However, though the rate of dilution will drop off to a very low level it will continue.  This is due to temperature exchange with the environment.  The air of the room, or your hand as you hold the glass.

Negroni

Negroni

For this reason, when mixing a cocktail by whatever method we stop once we have reached this Equilibrium of Temperature.  Our job is done.  The further expenditure of time and effort will not improve the final product.  Time to stop, straining the cocktail into its serving glass if appropriate, as for a Sidecar.  Serving it as is if not, as for a Negroni.

The second is that the time it takes to reach this Equilibrium of Temperature depends on the level of interaction between liquid and ice.  Now if you were to simply pour a drink over ice and leave it, then it would eventually reach an Equilibrium of Temperature on its own.  For a single drink, a time likely measured in a few minutes.  This is because the heat exchange between liquid and ice occurs solely between the surface layer of ice and the single layer of liquid adjacent to it.  The heat is then conducted through the rest of the liquid, which is a comparatively inefficient process.

But by agitating the drink we cause different layers of liquid to interact with the surface layer of ice.  This has the effect of speeding up the heat exchange.  And reducing the time needed to reach the Equilibrium of Temperature.  In general, the more vigourously we agitate the drink, the less time it will take to reach.  So while it takes only a few seconds to reach the Equilibrium of Temperature when shaking a cocktail, it may take up to a minute when stirring.

Dilution

The last is to consider how the quantity of ice added affects the resulting level of dilution.

Lets say I make two identical cocktails, and set them in mixing glasses ready to be stirred.  To one I add one cube of ice.  To the other I add ten cubes of ice.  All the ice is in contact with the liquid.  Which one will be diluted more?

Ice

Ice Cubes

At first glance you might think this a ridiculous question.  Surely the one with ten ice cubes will dilute more.  The melting of ten ice cubes is going to release ten times as much water as the melting of a single ice cube.

That’s true.  If we left the two cocktails long enough for all their ice to melt.  But we’re not going to do that.  We’re just going to take both cocktails to the point where an Equilibrium of Temperature has been reached.  At which point we’ll strain off the ice to prevent further dilution.

So the question becomes, how much dilution will occur to each drink by the time we reach this Equilibrium of Temperature?

In each case the ice must reduce the temperature of the same volume of liquid by the same amount.  As the single cube of ice does this it draws in the heat of the liquid, resulting in a certain degree of melting.  But the ten cubes can spread this temperature increase across ten times the volume of ice.  As a result, far less ice will reach the temperature threshold for melting.

So, although it might initially seem counter intuitive, the cocktail with ten times as much ice used to chill it will dilute far less than the one with a single cube.  Note that this won’t result in a tenth of the dilution as there are other effects involved.  But it will be a lot less.

For this reason, whenever you stir or shake a cocktail, you should always use as much ice as your mixing glass can hold.  Using less will result in greater dilution than you intend.

Surface Area

Once last point to consider when pondering dilution is the surface area of the ice you are using.  As stated, the actual melting of ice occurs at its surface.  This is where the temperature exchange occurs most readily.  As a result, increasing the surface area of the ice you are using will have two results.

Crushed Ice

Crushed Ice

The first is that the greater surface area allows for a faster temperature exchange.  The net result is that you will reach your Equilibrium of Temperature faster with a greater surface area for a set quantity of ice.  However, it should be noted that since this process occurs within a matter of seconds anyway, this difference is typically unimportant.

Second, you can expect to experience a greater level of dilution.

Mojito

Mojito

Though this is a matter of greater surface area, it isn’t really down to the heat exchange with your cocktail.  Instead it is due to the heat exchange with the environment prior to adding ice to your drink.

For practical reasons, ice is typically kept out in a room temperature environment, like an ice well.  Due to this it forms its own Equilibrium of Temperature with the environment, and is actually slowly melting.  So a thin sheen of water covers the surface area of each ice cube.  This contributes significantly to the dilution of a cocktail during chilling.  And as crushed ice has a far greater surface area than ice cubes, adding it to a cocktail results in significantly more dilution than for the same volume of ice cubes.

It is for these reasons that when we use crushed ice we typically Build a drink.  We make it in the glass we serve it in.  If we were instead to first shake it and then pour it over crushed ice the dilution would be too great.  It is also the reason why many drinks served over crushed ice seem to be very strong.  Like a Mojito or Caipirinha.  We rely upon this extra dilution effect to attain the correct strength.

True, if you were to take ice cubes straight out of a freezer you would avoid this extra dilution.  But it is only Alcoholic Powerhouses which would really benefit from the reduced dilution which would occur.  And ice out of a freezer sticks together, making it very awkward to deal with in any quantity.  So for the sake of efficiency, ice is kept out, and the resulting consequences for dilution must be considered.