In search of the perfect ice cube

Ice is ice, right? It’s cold, you put it in your drink and it makes your drink cold. Don’t put too much in because it will water your drink down. That’s all there is to it, right?

Wrong!

Ice and lime

Ice and lime

This is so far from the truth that it has long surpassed Jeffery Archer or Tony Blair and rammed itself firmly into some sort of racial memory of misguided logic. At least everyone knows politicians lie – the “Ice Fallacy” is so insidious and deeply entrenched that nearly everyone believes it.

But, times are changing. An army of people, led by the great drinking minds of our time and equipped with the cold, hard edge of science are charging head-long to vanquish this Usurper of Truth, who hath bought us naught but tepid, watery drinks. We have established a foothold and now it is time to expand and conquer the endless masses of the beguiled.

Okay, I am going to get a grip now, and lay the melodrama aside for the time being.

There are several factors that make “good ice” and I am going to explore some of them here.

But first, what makes “good ice” good? Well, you can use ice in different ways. When used in a cocktail shaker, you are looking for slightly different outcomes than the ice you drop in your glass. As an insatiable G&T aficionado, I am only going to consider the sitting-in-your-glass use; in this format, ice has two jobs; these are…

1)      Making your drink cold.

2)      Otherwise, not altering the overall experience of your drink.

The so-called “good ice” will do both of these jobs well.

Incidentally, in a cocktail shaker, you are actively looking for dilution (just a controlled amount), and if shaking, you might be looking for a texture or appearance change too.

 

The Water

Water

Water

Okay, this is probably the most obvious. If your water tastes like crap, your ice will taste like crap. Got lots of chlorine in your tap-water? Your ice will have lots of chlorine in. For six years, I lived in a house that had had its own borehole and the water was pure and sweet – unfortunately, this spoiled me something terrible and I could smell the chlorine in ice cubes made with tap-water. Drinking in pubs was a real problem for me.

But it is not just chlorine; there are loads of chemicals that are added to tap-water and they do impact upon the taste. It is amazing how you get used to drinking crap tap-water too. When I moved away from my house with the borehole and into a place with mains water, I nearly gagged when drinking from the tap – now I barely notice. However, if you are going to the trouble of sourcing good ingredients for your drinks, why drop in nasty ice to cool it down? What’s the point in using Martin Miller’s Gin, blended with the finest Icelandic glacial melt-water, if you are just going to add tap-water to it, in the guise of ice?

How far you actually go in solving the water problem is really up to you. Here are a few tips…

  • Buying bottled spring water is probably a good start. It will have all sorts of mineral impurities in, but not all impurities are bad, or affect the taste. Choose one that is good value and tastes good.
  • Boiling tap-water will drive off the more volatile impurities (like chlorine) and get rid of a lot of the other dissolved gasses (more on this in a bit).
  • Passing tap-water through a jug/cartridge filter will take out a lot of impurities and improve the flavour. This will take out a lot of the dissolved solids which may end up with you having flat-tasting water.

I would steer clear of buying deionised or distilled water for your ice – while it will make “good ice” in a mechanical sense, drinking water treated in this way can strip the body of minerals. Too pure isn’t good. Icelanders refer to deionised water as “Dead Water” because it is flat and lifeless. There is a balance to be had and neither extreme is good.

Mostly, I would recommend boiling the water first. If you have particularly hard water, then you might want to filter as well.

 

The science of cooling

Melting ice

Melting ice

Okay, this is where it might get a bit intense and nerdy but do persevere, as it’s fascinating stuff.

There are two mechanisms that ice uses to cool your drink. The first is a very basic concept that seems like common sense; the ice is cold, the drink is warm – the ice absorbs heat energy from the drink.

Simple, yes?

Well, not quite. There is this strange thing that some materials take more or less energy to heat up. One gram of water takes 4.18 Joules of energy to heat by one degree (Celsius or Kelvin) and one gram of ice (at -10oC) only takes 2.11 Joules of energy to heat by one degree. Incidentally, asphalt only takes 0.92 Joules, which is why the road is always really hot in the sun. These numbers are called the Heat Capacity of a material and all materials heat at different rates.

The good news for imbibers is that ethanol has a much lower Heat Capacity; 2.44 Joules per gram per Kelvin. Alcohol takes less energy to cool and heat than water; the stronger your drink, the easier it will cool.

So, were you to take 100g of ice at -20oC and pour over it, 100g of water at 20oC, you will end up with a 200g of water at 10oC (eventually), not ice floating in 0oC water. Well, that would be true if it were not for the second mechanism at play.

Ice, it turns out, doesn’t just start melting when it reaches 0oC. It actually takes quite a lot of energy to break that ice-crystal lattice apart. In fact, it takes 334 Joules of energy per gram to melt water ice – this is called the Heat (or Enthalpy) of Fusion. This is an additional requirement to the energy required to heat the material; so if you take 100g of ice at 0oC, it will take 33400 Joules of energy to melt that ice and end up with 100g of water at 0oC (no temperature change, just a phase change). That’s enough energy to heat 100g of liquid water at 0oC to a whopping 80oC! Is that mind-bending or what?

Also, get this: Water actually gives off heat when freezing as well as absorbing it when melting. This principle is being used to develop passive air-conditioning systems for buildings, using waxes that melt just above room temperature (go read about Phase-Change Materials if you are curious).

So, our 100g of ice at -20oC mixed with 100g of water at 20oC will do something like this. The ice will warm quickly and absorb 4220 Joules of energy, reducing the temperature of the warm water to about 10oC.  The ice then begins to melt; just less than 13g of ice melts, absorbing a further 4220 Joules of energy and the water reaches 0oC, without the ice changing temperature at all.

It isn’t quite as simple as this; the room will be imparting heat into the water and there will be temperature gradients in the ice as well as convection currents in the liquid.

There is also another quirk that stretches beyond the limits of my knowledge; it transpires that ice at 0oC can cool a drink to -7oC in a cocktail shaker. What? You don’t believe me? Go read this mind-blowing article, complete with proper science experiments: http://www.cookingissues.com/2009/07/22/cocktails-the-science-of-shaking/

Weird huh? I could speculate about the reasons, but that wouldn’t be cricket science.

Okay, that’s the science bit over, time to look at what we can do with this knowledge.

 

The temperature

Cold thermometer

Cold thermometer

This one is pretty obvious.

The colder the ice, the more it will chill your drink before starting to melt, which is good. This isn’t the most efficient means of cooling, but it’s a start. My domestic freezer is set to -20oC and this will suck out 10oC from an equal weight of liquid water – more from an alcohol-water mix. The more you cool your drink before the ice begins to melt, the less you dilute your drink by melting said ice.

 

The shape

Ice from an ice-machine - with dimples

Ice from an ice-machine - with dimples

Novelty ice-cubes in fun shapes and those odd cubes with massive dimples that come out of ice-cube machines all have a much greater surface area than the humble cube.

Ice melts at the surface of the mass and the greater the surface area, the more ice you will have melting at any given moment. While this will facilitate cooling, little lumps and nodules of ice (say, the neck of the novelty guitar ice cube, or the funnels of your ice Titanic) will heat to 0oC quickly and start melting before the temperature in the main body of ice has finished reached 0oC. So you will cool by melting before you finish cooling by ice-warming.

Air bubbles trapped in your ice, when breached as the ice melts, will result in a huge increase in surface area and the lumps between voids will melt very quickly. Boiling your water before freezing will drive off most of that dissolved gas and make a clearer, solid cube, with a crystal lattice with fewer faults.

A sphere of ice is the ideal shape, but they are buggers to make. You can buy moulds for ice-balls but they tend to be fiddly and inefficient on space. The humble cube is a good compromise unless you are seriously going to town on your ice.

You can buy equipment to shape ice-sphere if you are flush with cash and have nothing better to spend it on (Here is one of the cheapest I have seen).

 

The amount

Lots of ice

Lots of ice

There is some erroneous common-knowledge that putting too much ice in a drink will water it down too much when the ice eventually melts. This is pretty-much the opposite of the truth.

Ice melts when it warms to a certain temperature. There is only so much heat in your glass. The less heat each cube absorbs, the slower it will reach 0oC and start to melt. Therefore, sticking loads of ice in your glass will see each cube absorb less heat and staying solid for longer, thus keeping you drink cold without making it watery.

If you stick two small cubes in a glass, they will melt pretty quickly and water your drink down more than if you had filled the glass with ice to start with. You will also end up with a tepid drink.

More ice means less melting.

 

The size

Big ol' cube of ice

Big ol' cube of ice

Small ice cubes will suck heat out of your drink quicker than large cubes. This is because several smaller cubes have a greater surface-area for their volume than one bigger cube. There is more cold material in contact with your drink, so it will cool it quickly. Small ice is good for crash-cooling.

Larger ice cubes will cool your drink slower and therefore, more of the surface will melt by the time temperature equilibrium is reached and more of the cooling will have been achieved by melting.

However, once you have reached equilibrium, the larger cube takes-over in the efficiency stakes. Here, higher surface-area is a liability. You see, ice will be constantly melting at its surface; it is in a constant flux of melting and freezing. This is just the way things are when equilibrium is reached and normally the water freezes as fast as the ice melts (hence equilibrium). However, the materials in question are not the same. The ice is pure (ish) water and your drink is an alcohol-water mix and this freezes at a much lower temperature than pure water. In fact, a mixture of 40% ethanol and 6o% water freezes at -23oC (which is why your whisky never freezes when “on the rocks”), so when water is liberated from the ice crystal, into the ethanol solution, it is much less likely to re-freeze back into the ice. There are concentration gradients that complicate this, but this is the basics of how it works.

So, even at equilibrium, the ice in your drink will melt and the greater the surface-area, the more will be melting.

Ideally, you would crash-cool your drink with small ice and then quickly transfer it over to large cubes. This is way too much of a faff for almost everyone who might be considered sane, so large cubes tend to win-out.

 

Conclusions

In short, big ice cubes in very simple shapes work best. Make them as cold as possible, use good quality water and boil the gas out. Use lots of it and they will cool your drink and keep it cold for a long time with minimal dilution.

I personally use Tovolo Perfect Ice Cube Trays, which are silicone moulds that churn-out chunky 1½ inch (38mm) cubes. They last well through a long-nursed drink and there is always plenty of ice left when the glass runs dry. They can be hard to find in this county and are usually quite expensive when you do find them – on ebay, it often seems cheaper to buy them from the US and get them shipped to the UK.

Tovolo also do a “King” model as well that makes massive 2 inch (50mm) cubes.

There are all sorts of moulds and trays out there though. There are some that create spheres (without the massive expense) – in fact, it is rumoured that the queen uses spheres of ice in her drinks as they clink less in the glass.

One last thing; now that you are armed with this knowledge, don’t be an ice-bore. You won’t win friends by complaining about the ice at their parties, or in bars, and people will think you insane if you bring your own – there are times when you just need to be grateful that there is ice in your drink at all.

 

Creative commons image attribution

 

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5 thoughts on “In search of the perfect ice cube

  • March 10, 2012 at 9:33 pm
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    I enjoyed the science, but disagree with the conclusion. The idea that transferring is too much faff is just daft.

    One mixes the G&T in a cocktail shaker with a metric shedload of fine (or even crushed) ice, then strains it into a glass with large cubes.

    Reply
    • March 10, 2012 at 11:51 pm
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      This is cocktail-shaker territory and I think I stated in the opening paragraphs that I was only considering the in-glass ice. To be honest, even in a cocktail shaker, the speed of cooling will be quicker but the drink will dilute quicker too, so you aren’t really saving much apart from a few seconds of your own time. You actually look for some dilution in a cocktail shaker too, which is something you don’t typically want in a glass-mixed cocktail, like a G&T.

      Also, lots of crushed ice will provide a massive surface-area for the dissolved carbon dioxide to form bubbles on. It will foam-up and flatten your G&T before it even gets to the glass (an likely spill too). It would work well for a still cocktail, but not a fizzy one.

      Reply
  • March 11, 2012 at 7:13 am
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    I personally like to warm sugar in a pan with a little water until I have a thin syrup, then add tonic water (not diet – NEVER diet) and chill until cold.

    Once the syrup/tonic mix is cold, I pour in some gin, lime and lemon zests and juice, then freeze.

    Many recipes use a small amount of gin and freeze for a short time, I prefer using a larger amount and relying on the alcohol to prevent freezing solid.

    A quick mash with a fork and voilà: G&T sorbet.

    Although, I actually prefer just drinking the gin :)

    Reply
  • Pingback: » Ice CUBES? No thanks! Likely Moose

  • January 8, 2015 at 11:29 am
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    I bought some brain moulds. These work well as the fine ‘wrinkles’ melt quickly, rapidly cooling the drink, but the remaining, almost spherical, single large block of ice melts exceptionally slowly.

    A happy medium.

    Reply

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