Clear ice looks better, melts more slowly and tastes cleaner. You can make it at home with a small insulated cooler and a freezer.
Water in a standard ice tray freezes from the outside in. As the water freezes, dissolved air and impurities are pushed toward the center, where they are trapped as the last bit freezes. That trapped material is what makes the middle of a cube look white and cloudy.
Cloudy ice is not unsafe by itself, but it is more fragile and can crack, and it tends to melt faster, which means more dilution in your glass. It can also pick up the smells of the freezer. For an unhurried drink such as an old fashioned, ice quality matters.
Clear ice is made by freezing the water in one direction only. If the water freezes from the top down, impurities and air are pushed downward ahead of the freezing front, into the unfrozen water below. The ice that forms above stays clear, and the cloudy material collects in the last part of the block to freeze.
This is called directional freezing. It is the same principle that professional ice makers use, scaled down for a home freezer.
Use a small insulated cooler that fits in your freezer, with the lid off. The insulated walls slow freezing from the sides and bottom, so the top freezes first. Do not use a cooler that has held anything unsafe, and wash it well.
Fill the cooler with water, leaving an inch or two of space at the top for expansion. Many people use filtered or boiled-and-cooled water for a slightly cleaner result, though tap water works. Set the cooler in the freezer without the lid.
Once the block is out, you will see a clear upper section and a cloudy lower section. Set the block on a stable board over a towel. Trim away the cloudy part. Then score lines into the clear ice with a serrated knife, moving it back and forth like a small saw, set the knife in a score line and tap its spine gently with a mallet to split the block into cubes or slabs.
Work slowly and wear sturdy shoes and gloves if you like. Ice is slippery, knives are sharp and tapping with a mallet can send pieces flying. A wet kitchen towel under the board keeps it from sliding.
Keep the finished pieces in a sealed container or freezer bag so they do not absorb freezer odors. Before using, rinse them briefly and let them sit for a minute until the surface turns glassy and slightly wet, which helps prevent cracking when the drink hits them.
Use large cubes for spirit-forward drinks such as the old fashioned and negroni from the classic cocktails guide, since larger ice melts more slowly. For shaking, ordinary ice is usually fine, as described in the guide to shaken versus stirred cocktails.
Use a cooler that is clean and used only for food and ice. Check that it fits flat in your freezer, and keep the freezer itself clean so the ice does not pick up odors. Do not use a cooler with cracks or mold. Wash the cutting board and tools before and after use.
Handle ice with clean hands or tongs and store it in clean containers. If you are using filtered water, replace the filter on schedule. If your tap water has a strong taste, the ice will have it too.
Beyond clarity, the size of the ice affects how a drink behaves. A large cube has less surface area for its volume, so it melts more slowly and chills a drink gently over time. Small cubes and crushed ice melt faster and suit drinks that should be diluted quickly, such as those served in tall glasses.
Cut some pieces as large cubes for rocks glasses, some as slabs or spears for tall glasses, and keep a few small pieces for shaking. The glassware guide shows which glass each shape suits.
If the cooler method is more than you want to do, there are simpler ways to improve ice. Use large silicone molds for slow-melting cubes, even if they are slightly cloudy. Use fresh, filtered water. Keep ice covered in the freezer and replace it regularly. Some people buy purpose-built directional-freezing molds, which apply the same idea in a smaller, tidier form. Each improves a drink, even if none is perfect.
If you share a freezer, keep the cooler level and out of the way of other items, since a tilted block freezes unevenly and the clear section ends up thinner than you hoped. A level shelf and a little patience are the whole trick.
If your block comes out mostly cloudy, the cooler may be freezing from the sides too quickly, or the freezer may be very cold. Try a different cooler, or a smaller batch. If the block cracks during removal, let it temper a little longer. Fine cloudiness is normal near the bottom.
If you plan to serve many guests, a cooler batch can be cut ahead and stored. For a party where you are batching drinks, see the batching guide. For a large event, ice planning is part of what private event service handles.
It is optional. Boiling and cooling removes some dissolved air, and some people feel it helps, but directional freezing is the main factor.
The cloudy part is expected. It is where impurities collect at the end of freezing, and you cut it away.
Roughly a day or more, depending on your freezer and cooler. Check progress rather than relying on a fixed time.
It can taste cleaner because it avoids trapped air and impurities, and it usually melts more slowly in the glass.
Ask about a table, an event date or a class and the operator will reply with what is possible.