How to make clear Ice for cocktails

Alternate Title: “If it’s not perfect, what’s the fucking point?”

My name is Ben. I like it when things are done properly*. This post, therefore, has been quite a while in the making.

It turns out making clear ice is hard. Very hard in fact. There’s a very good reason that companies like this exist. In fact, if you’re based in, or near, London – you should probably just stop reading this, man up, buy yourself a chest freezer to house some of their wares, and give them a call.

If like me though, you’re out of their delivery range, you’re going to need to make your own**.

Luckily, every single one of you has the requisite equipment for this, so there really aren’t any excuses. You can make big, clear ice with zero investment. Sounds like I’m trying to get you to buy a timeshare. I’m not. Promise.

“Why is clear ice so important” I hear you cry? Three reasons:

Firstly, Aesthetics. A massive chunk of clear ice floating in a drink looks amazing. Don’t underestimate the ‘first bite’.
Secondly , Dilution. A massive load of little microscopic bubbles in your ice (that’s what the cloudiness is) has the effect of hugely increasing the surface area of your block of ice, meaning it’s going to dilute your drink much faster.
Thirdly – Stability. Even assuming you take your ice chunk out of the freezer and let it temper properly, it’s going to be much more likely to crack into smaller pieces (and we’re back to point 2 – dilution) if different areas of the chunk have different densities.

Before we get onto the recipe – a bit about the theory behind this (or my hideously simplistic interpretation of it at any rate). There’s no shortage of people that will tell you that all you need to do to make clear ice is boil it. Or boil it twice. They are wrong. There are also people that say that all you have to do is use Bottled water, or filtered water. They, also, are wrong.

I’m going to use water that’s both filtered and boiled in my method below, but neither (or both) of these methods alone produces clear ice. The problem is actually pretty straight-forward once you take the time to sit down and think about it. It’s just simple state-change dynamics.

Y’see ice has 3 particular properties that make our lives very tricky when we’re trying to make a massive block:

1) Ice is less dense than water (0.92 is the exact figure), which means that water expands as it freezes.
2) Ice isn’t gas-permeable (at least not to the degree we’re talking about here)
3) Ice freezes from the outside in

Imagine for a moment, a block of ice thus:

Why red pen, Ben? Ice is Blue, everyone knows that.

The outside of that block is frozen solid and impermeable (well, impermeable-ish – it will expand when pushed, but won’t let gas through), but the inside is still liquid. As the liquid freezes, it expands into the ice shell. This places a negative pressure on the liquid inside the block, meaning bubbles are going to form. These bubbles aren’t necessarily dissolved gases – they could just as easily be water vapour. Remember, Zero Degrees*** isn’t just the state-change point of water into ice – it’s the Triple-Point, so water-vapour can exist here and will certainly form when the liquid water is exposed to a lower-pressure system.

That’s what I reckon anyway.

Commercial ice-making machines use either controlled directional freezing (this video is an excellent demonstration of this) , or, for smaller cubes, a cold-plate ‘layering’ technique that ensures that the freezing surface constantly has liquid water venting over it to ensure there’s somewhere for the dissolved gases to go (back into solution). It’s well worth a look inside the ice machines they use in fast-food restaurants / bars if for nothing other than curiosity.

It’s worth noting that I tried the directional freezing method at home before settling on this one, and it works. Read Camper English’s Alcademics Blog all about it here. Now read the rest of the articles on there. They’re ace.

The reason I ultimately ended up discounting this method for my own personal use is that it takes a pretty long time to generate just one ice-ball. If you’re after a load of them for a party, it’s just not feasible. Likewise I discounted this (incredibly clever) method because I haven’t got room for a massive coolbox in my freezer (and I don’t think many people do).

I was after a solution that was practical, can be executed using close to no space in the freezer, and didn’t require any equipment. And I think I’ve got it.

So. Here we go. You get pictures too, you lucky lot:

Get yourself a pan. A clean pan. Really clean. Now clean it again, and wipe it out properly with Kitchen Towel. It, erm, has to be clean is, I suppose, the general message.

Fill it up with filtered water****. You want about 3 litres. Carefully. Try not to knock any air-bubbles into it. I’m filling this from a Brita Filtered water tap I’ve got at home, but water from a Brita Filter Jug is just as good.

Bring to the boil, and simmer for about 3 minutes. This will knock any dissolved gases out of solution.

Carefully tip the water into a stainless steel bowl, and leave it to cool to room-temperature. You can cover it loosely with a tea towel to stop anything falling in, but don’t cling film it. We want to allow any residual dissolved gases to escape.

Very carefully transfer approximately 1.5 litres of the water to a plastic freezer box. You want to minimise any splashing at this point, as you’ll re-incorporate those pesky dissolved gases.

Sling it in the freezer.

After somewhere between 2 and 5 hours depending on how buff your freezer is, you’ll have a block that looks something like this. Look carefully, you can see the central reservoir of water. The ice has formed perfectly clear, and pushed all the dissolved gases (and water-vapour if that’s what we reckon’s going on) into the reservoir. Here comes the clever bit:

Remove the partially frozen ice block from the freezer, and make a hole in it. Drain out and discard the reservoir-water, then re-fill the hole with more of the boiled water from earlier (remember you had 1.5 litres left over?).

For the best results here, you’ll want to pop the stainless bowl in the freezer for about half an hour just to take it down to zero degrees. This stops the additional water we add from dissolving too much of the outer shell. Don’t be tempted to re-freeze the shell before tipping the chilled water in, as the difference between freezer temperature and the zero-degree water will shatter the fragile shell. I know whereof I speak.

Now pop the block back into the freezer and give it another couple of hours. Then pop it out, and repeat the drain/refill process. Now leave the block overnight to set solid.

When you remove the block from the freezer, you can clearly see two ‘attempted cloudy spots’ which have been pushed progressively further inwards by our drain/re-freeze procedure. This, incidentally (and I’m sure you all thought this earlier. Dincha. Dincha?) is the reason that just freezing a big block and leaving it alone isn’t good enough – the inch or so that’d be left around the outside of the block isn’t thick enough to provide us with a meaningful chunk. The reason that the block looks cloudy at this point incidentally is that by pouring in fresh water to the top of the void in the ice, we create a new, very thin layer of ice on the top of the block that needs chipping off. You can see that top ‘strata’ more clearly a bit further down.

This is the bit you’ve been waiting for – split the block in half using an ice-pick (we’ve got some cool ones here).

As well as that clearly-defined ‘strata’ of new ice on top, you can see that the cloudy void created is both very small, and very well-defined.

Now comes the fun bit. Chip the block apart (working around the cloudy void) with your ice-pick into hunks that are big enough to be impressive, whilst being small enough to fit in your glasses. You can see from this image that there’s really very little waste. This includes the middle bit, and all the ancillary chipping…

And there we go. A big tray of lovely, clear, long-lasting, pure-tasting ice. Winner.

I picked a chunk at random so that you can see the quality – it’s pretty darned close to perfect (perspective/refraction through liquid’s a bitch, but that chunk is actually as big as the glass is wide). There’s a tiny bit of haze on one side which is from one of the attempted cloudy spots. I could have been more thorough with the chipping process, but to be honest if there’s a tiny bit of haze left on the outside of a chunk, it’ll disappear pretty quickly due to the increased rate of melting in that sector of the chunk.

There we go then.

If you’re having a crack at this at home – don’t forget to tweet some photos to us @masterofmalt – we’d love to see how you get on, and remember, you’ll need one of these chunks for this week’s #MasterofCocktails recipe – The Highball. You can tune in at 6pm on Sunday night on twitter, or alternatively catch up on this very blog on Monday, when we’ll publish the full recipe.

Toodle-pip.

Ben

* I’m almost certainly on some sort of spectrum or have something that has an acronym of some kind, but opening that whole analytical box of frogs isn’t something I’m particularly keen to do today.

** Not necessarily true. I did at one point give very careful consideration to taking a suitcase, some tin foil and a load of bubble wrap up to London, and simply collecting a chunk. In fact I may still do that. Stop judging me.

***Okay, 0.01 degrees c, not Zero. Pedant.

**** Filtered water, not mineral water. You want impurities out, not minerals (for which read impurities) in.