Ice and dilution: the ingredient you never measure

Every cocktail has one ingredient that never appears on the recipe card. Water, delivered by melting ice, makes up a fifth to a quarter of a finished Old Fashioned or Daiquiri. Ice decides how cold the drink gets, how fast it softens, and how it looks in the glass. Treat it as something you choose and measure, the way you would a syrup.

What you need

• Freezer space for a small hard-sided picnic cooler, about 6 to 9 quarts (6 to 9 liters).
• Tap or filtered water. Boiling and purifying help a little; the freezing direction does most of the work.
• A serrated bread knife, a rubber mallet or hammer, and a clean tea towel.
• Silicone trays for 1 inch (25 mm) cubes and, if you like, a 2 inch (50 mm) cube tray.
• Zip bags or a lidded tub for storing cut ice.

Why ice goes cloudy

Water pushes dissolved air and minerals ahead of the ice front as it freezes. In an ordinary tray the ice grows from every side at once, so the impurities are trapped in the middle as a white core. Camper English's directional freezing idea, published in 2009, removes the problem by letting the water freeze from one side only. The clear ice forms first; the cloud collects in the last part to freeze, and you cut it off.

Steps: clear ice in a cooler

1. Fill the cooler with water, leaving 1 to 2 inches (25 to 50 mm) of headspace for expansion.
2. Put it in the freezer with the lid off or propped open. The insulated walls and base slow freezing from the sides, so the block grows from the top down.
3. Wait. Timing depends on the cooler and the freezer: Cocktail Society reports 24 to 30 hours for a small cooler; English reports several days on a cold setting for a larger one. Check after a day. You want a clear slab with a layer of cloudy ice or unfrozen water at the bottom. If you pull it early you lose nothing but volume.
4. Take the cooler out, turn it upside down over the sink, and wait a few minutes for the block to drop. Pour off any trapped water.
5. Let the block rest on a towel for 5 to 10 minutes until the surface starts to glisten. Cold, dry ice shatters along random lines; tempered ice cuts where you tell it to.
6. Score a line across the block with the serrated knife, sawing about 0.5 inch (1 cm) deep. Set the blade in the groove and tap the spine with the mallet. The block splits along the score. Cut away the cloudy base first, then cut the clear slab into 2 inch (50 mm) cubes or spears sized to your glasses.
7. Bag the pieces and return them to the freezer. Rest them 5 minutes before use so they do not crack in the drink.

Which ice for which glass

• Shaking and stirring: solid 1 inch (25 mm) cubes, dry from the freezer. Hollow tube ice and thin bagged wafers melt too fast to control.
• On the rocks: one large clear cube or spear that nearly fills the glass. The Old Fashioned over a 2 inch cube stays cold through a slow drink and gains water slowly, because one large piece has less surface than a glass of cubes.
• Highballs: fill the glass to the top with cubes before the spirit goes in. The Japanese Highball is built this way: a glass packed with ice, whisky stirred to chill, then soda poured down the side. More ice means less melting, because the drink gets colder and stays there.
• Crushed ice: for juleps, swizzles and tiki drinks only, never in the shaker, where it dilutes unpredictably.

How much water a drink takes on

Simon Difford's measurements with his ice put a standard shake at about 25 percent dilution and a stir at about 20 percent. Dave Arnold's probe readings tell the same story from the temperature side: a shaken drink lands near minus 5 to minus 7 C (23 to 19 F) and a stirred drink near minus 1 to minus 3 C (30 to 27 F), and the colder drink has always taken on more water, because melting is the only way the ice can chill it.

That figure is why a batched stirred drink gets 20 to 25 percent water added before it goes in the freezer. The bottle will never meet ice, so the water that a stir would have added is poured in by hand: for a 2.5 oz / 75 ml Manhattan, roughly 0.5 to 0.75 oz / 15 to 22 ml of still water. Stronger drinks sit at the top of the range, lower-proof drinks such as a Negroni at the bottom.

Some drinks want more than a shake gives. Difford's adds a measured 10 ml (about 0.33 oz) of chilled water to a Daiquiri made with dry ice, and omits it when the ice is wet. A measured splash is repeatable; shaking longer is not, because the drink stops changing after about 12 seconds.

What can go wrong

• The whole block is cloudy. The lid was on, or the freezer was so cold the sides froze with the top. Prop the lid, raise the freezer temperature a little, and pull the block earlier.
• The block cracked while cutting. It was not tempered. Rest it longer before scoring.
• Cubes crack when the drink is poured. Same cause. Rest cut cubes 5 minutes out of the freezer before use.
• Drinks taste flat or watery. Wet ice. Ice that has been sitting in a bucket carries a film of water into the tin. Drain it or use fresh.
• Drinks taste harsh. Too little dilution. Stir longer, or add the measured splash.
• Off flavors. Ice picks up freezer smells. Store cut ice in sealed bags and use filtered water if your tap water tastes of chlorine.

Food safety

Ice is a food. Make it with potable water, handle it with a clean scoop or tongs rather than hands or the glass itself, and never return ice from the shaker to the bin. Discard shaker ice after every drink.

Sources

• Camper English, "What is directional freezing?" and "Clear ice blocks at home in an Igloo cooler", Alcademics.
• Cocktail Society, "What is directional freezing?".
• Simon Difford, "Ice: clear, cubed and crushed" and "Some cocktails benefit from added water", Difford's Guide.
• Dave Arnold, "Cocktail Science in General: Part 1 of 2", Cooking Issues, 2010.
• Punch, "The essential guide to batching and freezing cocktails".