Correct brewing temperature and time. Fully automatic. Durable. O-ring seal is effective and reliable. Interior parts can easily be kept free of rancid coffee oils.
Negative Product Points
Decades since commercially available, so relatively hard to acquire. Units offered through thrift stores/rummage sales/eBay could have condition problems unrecognized at the time of sale.
Construction: This is a superb sample of electro-mechanical engineering, built to quality standards rarely seen these days. The pot and upper vessel are made of heavy copper and beautifully chrome-plated to a mirror finish. The seal between them is by a thick rubber O-ring. The stainless steel filter has two stages, a coarse disk and an exceedingly fine mesh disk. Some versions include an additional cloth filter to insert between the disks.
Brew quality: As good as any I have tasted. Brewing temperature is correct and consistent. Coffee oils are not filtered out. The chromed interior and stainless steel filter equal glass in not imparting an off-taste. The filter screens allow a very slight turbidity in the coffee unless combined with the cloth filter, a matter of preference—some like to experience the suspended fines. Both ways are delicious to me.
Procedure: Pour desired quantity of water in the bottom. Attach the filter. Give the upper pot a little twist back and forth to make sure the O-ring fits into its groove in the lower pot, then lower the bakelite handles to seal top to bottom. Add desired quantity of grounds to the upper pot. Plug the cord in. Put the cap on. Turn the knob to brew. Coffee will be ready in twelve minutes or so. Water in the lower pot must heat to boiling, so the time to brew depends on the amount of water and its temperature. You don't have to attend to anything. The system goes through its cycles, ending with suction into the pot. A thermostat maintains finished coffee at drinking temperature. After removing the top vessel, you may fit the cap on the pot for serving, or transfer the brew to an insulated container.
How it works (from web research and inference based on observation.): Pressure and temperature build in the lower pot in about four minutes, sending a large batch of brewing-temperature water into the top to mix with the grounds. (This is different from Cory, Silex, and other glass pots that initially send up lukewarm water.) Some water remains in the bottom for conversion to steam, which bubbles up through the brew in the top vessel. This steam maintains the brewing temperature as it re-condenses. It also vigorously agitates the coffee slurry. (I have measured the brewing temperature in four different C-50 units—all near 205 F, the design temperature.) After the lower pot boils dry, a thermostat triggers to a lower heat setting. Next, the lower pot cools off until its residual steam condenses, creating a vacuum, which then quickly pulls the brewed coffee down through the filter into the pot. From start to finish takes about twelve minutes.
Comparisons: After decades of brewing with the trusty Chemex glass plus filter-paper drip system, I found that antique glass vacuum brewers could make coffee just as well and perhaps better. Since these Pyrex vacuum makers had an important advantage--not requiring constant attention to pouring and to water temperature--I moved to this more efficient system. But still, glass vac-pots need to be watched carefully to time the brewing process, and are extremely fragile. When I discovered that the rugged Sunbeam Coffeemaster vacuum brewers make equally fine coffee, but totally automatically, I converted again.
Care: Wash off grounds from the filter. The pot and upper vessel may be washed inside and out with soap and running water, but don’t immerse the sealed electric base of the pot in water. That’s it, except I recommend occasional use of household ammonia to rid the filter and interiors of nearly invisible accumulations of dried coffee oil. I protect the mirror finish from scratches by placing the parts on a dish-towel while cleaning.
Source, eBay. Average price from 24 units I observed auctioned in summer of 2005 was $42.47. High = $112.50, low = $8.99. I shudder to think how much a new machine like this would cost today. Of complex curved shapes, all copper, with heavy chromium plating, highest quality electrics--it would probably be in the hundreds of dollars.
Three Month Followup
One Year Followup
I’m still loyal to this superb coffee maker. After brewing many hundreds of times by now, I have found that there are many ways to make errors—all from not paying attention to the simple procedures. Should one be distracted or half asleep, it’s easy to omit: loading the coffee grounds, putting in water, plugging the unit in, switching the knob to High, or pushing the handles down. The worst consequence of these goofs has been temporarily delaying a caffeine “fix.”
For the inevitable coating of invisible dried coffee oil I found a much more effective cleaner than previously recommended ammonia. Available through coffee merchants, a product called Urnex Cafiza does the job perfectly. About once a month I brew three cups of water with a teaspoon or so of this powder dissolved in the bottom pot. The brewing procedure is the same except not to add coffee grounds in the top. After the cycle finishes, the solution is colored tan and the C-50 interior and filter gleam like new.