Hoyer Freezer

Okay -- the mix is flavored and ready to go to the Freezer. It doesn't have to go very far, though -- just to the center of the production room, where a huge stainless steel box sits, ready to freeze about 750 gallons of flavored mix per hour. We often refer to our freezer as "The Hoyer", because that's the name of the company that makes it, but technically it's known as the Continuous Freezer because it operates in an ongoing, or "continuous" process. In other words, the mix is pumped in on one side as ice cream is continually pumped out the other (until the mix is gone, or until we make more!).

Once the base mix has been flavored, it is pumped through to the Continuous Freezer where the temperature drops and air is added. Certainly you knew that the freezer would cause the temperature of the mix to drop, but did you know that air was added at this point in the process? The amount of air added makes a huge difference between an "OK" batch of ice cream and a super premium batch. Too much air creates a light, fluffy type of ice cream. Some manufacturers add as much as 50% air to their ice cream (that's the legal limit), but Ben & Jerry's only allows for approximately 17%-20% air. This assures that the ice cream will be rich and creamy.

In the ice cream manufacturing world, the process of adding air is known as whipping. When the mix is whipped inside the freezer, tiny air cells are created. These cells increase the volume of mix. The additional volume produced is called overrun. In other words, the higher the overrun, the less ice cream and the more air will be in the product. Super-premium ice cream has a very low overrun, which means more there's actually more ice cream in your ice cream container (which tastes a lot better than air, in our opinion..).

The freezing process of the flavored mix accomplished at the Continuous Freezer is the first of two freezing phases the ice cream will go through before the product is complete. The second phase, when the ice cream is frozen solid, occurs much later in the ice cream making process. The process that occurs at the continuous freezer brings the temperature of the base mix down from 36 degrees, which is required for the holding tanks, to 22 degrees which is the freezing point for the mix. The speed at which the freezing occurs plays an important role in creating the perfect texture of the ice cream. While the mix is dropping in temperature, some of the water in the mix is freezing.

The freezing of the mix, combined with the whipping action, causes ice crystals to form. The speed of this process is crucial, because the faster the freezing, the smaller the ice crystals. Small ice crystals create a smoothly-textured ice cream (that's good). Large ice crystals give the ice cream an icy texture (that's yucky).

Here are a few more details that help explain how the continuous freezer does what it does:

First, the flavored mix is pumped into the freezer cylinder at a constant and controlled rate. Next, air is pumped into the cylinder at a constant and controlled pressure. Then the air and the mix are whipped at a constant rate by the agitator while the cylinder is cooled by the refrigerant. The refrigerant that we use to freeze the flavored ice cream mix is called liquid ammonia. Finally, the frozen flavored mix is pumped out of the cylinder at, you guessed it, a constant and controlled rate.

If you take a more detailed look in the freezer, you'll see that there are actually two cylinders working on that mix. The first cylinder freezes some of the mix and the second cylinder freezes the rest! Inside each cylinder there is an agitator called a dasher. The dasher is basically a tube with holes in it, with scraper blades attached. The flavored mix flows throughout the dasher as it is pumped into one end of the cylinder. As the mix is being whipped by the dashers, it comes in contact with the outer walls of the cylinder. At this point, the mix freezes and is then scraped off with the scraper blades. The dasher does a double job by whipping air into the mix at the same time as it's scraping what the mix is turning into -- ice cream!

What causes that mix to freeze on the cylinder walls? The inner cylinder walls are kept frozen because they're "jacketed" with an outside wall of refrigerant. One side of the cylinder is flooded with very cold (very, VERY cold) liquid ammonia. The ice cream mix flows on the inside of the cylinder and when it is "dashed" against the cylinder wall, it freezes.

Can you eat this stuff yet? Sure, but wouldn't you rather wait until we throw in some humungous chunks, or maybe a fudge swirl? How about a nice package to hold it all?

We're almost there, after these quick stops at the Variegater and the Fruit Feeder...