How to Make Clear Ice

Ordinary freezer cubes are cloudy because they freeze from every side at once. Dissolved air and minerals get pushed toward the middle, where they end up trapped as a white, bubbly core. That cloudiness is harmless, but clear ice looks striking in a rocks glass, melts a little more predictably and does not crack apart as readily in a drink.

The home method that reliably works is directional freezing: insulating the sides and bottom of the water so it freezes slowly from the top down, pushing impurities ahead of the freezing front. This guide covers the setup, how long to freeze, how to harvest and cut the block safely, and why tricks such as boiling water rarely work on their own.

Why freezer ice turns cloudy

Water holds dissolved gases and minerals. As it turns to ice, the growing crystals push those impurities out into the remaining liquid. In an open tray the water freezes from the top, bottom and sides at once, so the impurities have nowhere to go and get locked in the center as white streaks and bubbles.

Directional freezing gives them an escape route. If the water freezes only from the top surface downward, the impurities keep being pushed toward the bottom, and the upper part of the block forms clear.

Setting up directional freezing

Use a small hard-sided picnic cooler that fits in your freezer with the lid removed; around 4 to 6 liters (1 to 1½ gallons) is manageable. Its insulated walls and floor slow freezing from those directions, so the cold comes mainly through the open top. Fill it with filtered or plain tap water, leaving a few centimeters of headroom for expansion, and set it level in the freezer.

There are also purpose-made clear ice trays that use the same principle with an insulated outer box and silicone molds on top. They produce ready-shaped cubes or spheres and save cutting, though each batch is small.

• Cooler: small, rigid, lid off, level in the freezer
• Water: filtered tastes cleaner, but tap water still freezes clear with this method
• Freezer: leave space around the cooler for airflow

How long to freeze and when to pull it

Timing depends on the freezer temperature and cooler size. For a small cooler in a home freezer at about -18°C (0°F), check after 18 hours and expect it to take roughly 18 to 30 hours to reach the stage you want. Ideally the top two-thirds or so is solid and clear while the bottom is still partly liquid.

If you leave it until it freezes completely, the bottom section turns cloudy and pressure can crack the block or the cooler. Pull it a little early instead. Turn the cooler upside down over a sink or tray and let the block slide out, pouring away any remaining water. If any cloudy ice is attached to the bottom, it can be cut off after tempering.

Tempering, scoring and cutting

Ice straight from the freezer is so cold it shatters unpredictably. Leave the block on a towel or cutting board for 10 to 20 minutes, until the surface turns glossy and wet and it stops crackling. Tempered ice splits cleanly along a scored line.

Score a straight line about 5 mm (¼ in) deep across the block with a serrated bread knife. Set the knife's spine or a dull chisel in the groove and tap it firmly with a mallet or rolling pin; the block should split along the line. Cut slabs first, then bars, then cubes about 5 cm (2 in) on a side. Work on a towel, keep fingers clear of the line of strike and wear cut-resistant gloves if you have them.

• Slabs, then bars, then cubes or spears
• Trim any cloudy section and discard it or use it for shaking
• Ice pick: chip corners for rough-hewn shapes

Storing finished ice

Cut cubes stick together if bagged while wet. Spread them on a tray and refreeze for an hour, then store in a sealed freezer bag or lidded container so they do not pick up freezer odors. Use them within a few weeks; ice slowly sublimates and absorbs smells over time.

Take cubes from the freezer a minute or two before using them so they lose any frost and do not crack when liquid hits them. A clear cube in a rocks glass looks best with stirred, spirit-forward drinks and long highballs.

Shortcuts that rarely work

Boiling water once or twice removes some dissolved gas, but it does nothing about the direction of freezing, so the center of the cube still clouds. Distilled water has fewer minerals, yet it also clouds in an ordinary tray for the same reason. Freezing more slowly by turning up the freezer temperature helps slightly. Insulation that controls the direction of freezing is what actually makes the difference.

Common questions

Is cloudy ice bad for drinks?

No. Cloudy ice is safe and works perfectly well. It may melt and crack slightly faster, and it looks less polished, but the difference in flavor is minor.

Can I make clear ice in a silicone mold?

Not on its own, because a mold freezes from all sides. Place the mold in an insulated box or use a purpose-made clear ice tray that controls the freezing direction.

Why does my clear ice crack in the glass?

It went straight from a very cold freezer into a room-temperature drink. Let cubes temper briefly until the frost disappears before you pour over them.