Making Clear Ice – Part 2 of 3
Like diamonds, the attraction of clear ice isn’t fully understood, but it does look good in a drink. As we discussed in the previous post, the problem with making clear ice is that water doesn’t willingly transform into flawless crystals cubes, it chooses instead to go mirror cracking ugly when frozen because of its non-conformist behaviour of expanding when it forms a solid. Since we’ve learned how water behaves when it turns to ice, we can adjust the physical environment to accommodate these variables, which should lead to crystal clear ice.
For this experiment I designed an “apparatus” that increased the rate of ice formation at the bottom of the vessel, while keeping the surface from freezing over. The basis of the apparatus was to create a temperature differential between the top and bottom of the water. Even a slight, but constant temperature difference is enough to freeze the water at the bottom faster. This doesn’t stop it from freezing on top, but an air pump will fix that.
Since the budget for Art of Drink is pretty much zero, and my workmanship is at best a hack, I drew this pretty diagram to help visualize how this works instead of including a picture.
To start, you need a medium sized container, anything plastic will do, but short and wide is better than tall and narrow.
Next, you need to create a “heat sink” that will draw heat away from the water at the bottom of the container. To do this, drill some ½ inch holes into the container, about 2 inches from the bottom, and insert lengths of copper pipe that are 10-20% longer than the base of the container. These overhanging pieces of pipe will help to conduct the heat away by increasing the surface area. Any metal pipe will work, but plastics like PVC will not.
Fill the bottom of the container will metal (steel shot, nails, scrap metal from crashed UFO in backyard, etc.). This extra mass will improve the capacity of your heat sink. If you use roofing nails, like me, make sure you cover them with a metal “lid”, like an old cookie sheet, otherwise they’ll puncture holes in the garbage bag you’re going to be using.
Technically, a solid metal base would be ideal, but sometimes you have to work with whatever materials you have on hand.
After retrofitting the base of your container, place an extra-duty garbage bag into the container and ensure that the bottom makes good contact with the metal. Fill the bag with water, preferably filtered or distilled. Boiling isn’t necessary since the next steps will negate that effort.
Acquire from your local pet store an aquarium air pump, an air stone and some tubing. From your closet acquire a coat hanger. Using the coat hanger, with the tubing loosely wrapped around it, try to position the air stone in the middle of the container, an inch or two from the surface of the water.
The air pump and air stone will keep the surface of the water moving, and also circulate the water enough to make it difficult for the water to freeze. As long as there is a hole, with liquid water still present, the water will have somewhere to go as the ice forms. This avoids trapping the liquid water in an enclosed space and prevents the fracturing of the ice as discussed in Part One of of this series.
My first attempt used an aquarium “power-head” which is basically a water pump. Because of the relatively low volume of water I used, the heat produced by the pump was enough to keep the water from freezing for three days and that’s when I changed plans and used an air pump instead.
The final step is to find some place very cold, like Canada or a walk in freezer. Ideally, you’ll want the temperature to be about -10°C (23°F) since water has a very high heat of fusion (80 calories/gram). This means for every gram of water, you need to remove 80 calories of heat to turn it into ice. For 10 litres (2½ gallons) of water that means you’ll need to extract 800,000 calories. Please note that a dietary calorie is actually a kilocalorie or 1000 calories, so in food terms you need to remove 800 calories or 200 grams of sugar worth of energy.
During this experiment the temperature ranged between -15°C and -4°C, which means it took about 3 days for the water to freeze.
Surprisingly this Franken-Fridge actually worked. The bottom layer of ice was mostly clear and about 5-7 cm (2-2½ inches) thick, while the surface was partially frozen, but where the air was bubbling, the water was still liquid. The picture below is of a softball size chunk of the ice.
Because the garbage bag in the container was wrinkled, I had to break the ice into pieces since embedded garbage bag isn’t a good look. However, this breaking of the ice into random shapes with angular edges was actually very visually appealing. Much like a diamond, all of these angles reflected the light creating a really bright, sparkly piece of ice. This is what you really want in a drink.
The process works, but it isn’t very efficient nor is it practical. It’s a great way to make clear ice for drink photography, but if you run a bar or are hosting a serious party you’ll need to look to the professionals to get clear ice.
If you want to make blocks of clear ice, you can purchase a specially designed Clinebelle Carving Block Maker for around $6000. This will make two 300 pound blocks every 3 to 4 days. I recommend buying the hoist since you won’t be lifting these blocks without one.
The second, and better option is to order your ice from a company like Ice Culture who produce clear ice blocks for a living. I’ll have a full write up on Ice Cultures in Part 3 of this series.
If you’ve found this post informative and entertaining please consider purchasing a copy of Fix the Pumps to help support Art of Drink.