The official, patented name for the little plastic Ping-Pong ball contained in pint cans of Guinness and some other beers from the UK. Some people call it a widget.
This device is responsible for the extra-creamy head produced by these cans. Apparently the taps used to pour the beers (Guinness, at least) add nitrogen to the mixture, which is what the Smoothifier seeks to recreate. According to the patent text, here is how the device works its magic:
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A hollow plastic spheroid, about 2cm across, is blow-molded with pure nitrogen gas, and a small hole (0.61mm) is punched in it with a laser. This is placed in the bottom of the empty can.
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Beer is poured into the can, containing nitrogen in solution as well as the usual carbon dioxide. The can includes about two ounces of expansion room for the head, which fills as the beer is added and displaces any remaining air. A small amount of liquid nitrogen is also added to the can before it is sealed.
- The beer is heat pasteurized in the can; the liquid nitrogen changes to gas, increasing the pressure inside the can to nearly two atmospheres (in the case of Guinness), and forcing beer into the plastic widget through its tiny hole. When the beer is stored, the foam gradually settles back into liquid form.
- When the finished product reaches the consumer, the can is opened and decompresses to atmospheric pressure. The nitrogen gas inside the Smoothifier expands as well, sending a jet of trapped beer out through the hole. This brings the dissolved nitrogen out of solution, creating the thick, pub-style head, which quickly fills up its two-ounce expansion space. The expulsion of the beer from the pod also makes a characteristic squeaking sound, which you may hear as you open your can.
The key to the texture of the beer as delivered on tap, or in the special can, lies in the fact that the bubbles produced by nitrogen are much smaller than CO2 bubbles (like in Budweiser), so the head contains more beer and less gas. The popularity of the widget can is also assured by people like me, whose enjoyment of the beer itself is only heightened by our geekly fascination with the ingenious delivery system.
Credits:The bulk of this information is also found in this writeup by bozon. The original info is from the Unofficial Guinness FAQ and Folklore Page at http://www.ivo.se/guinness/. The patent, held by Arthur Guinness, Son & Co., is number 4,832,968 in the database at http://www.uspto.gov/.