History

Hot fluid bed roasting was invented by Michael Sivetz, a Chemical Engineer, in the 1970's as an alternative to the more popular drum roasters that he encountered on the market.

Sivetz noted that with drum roasters, the chaff that comes off the coffee beans continues to tumble with the beans as they are roasting. As the heat increases, the chaff chars, which creates smoke. The smoke deposits unwanted off-flavors on the beans themselves. This is why many people say drum roasted coffee beans taste burnt. The darker the roast, the more pronounced these flavors become.

Alternatively, the Sivetz “Fluid Bed Roasting Method” uses hot air to heat the beans while also tossing and mixing them for even roasting. The hot air moving through the beans also serves to remove the chaff as it's shed from the beans.

A “fluidized bed” is simply a bed of solid particles with a stream of air passing upward through the particles at a fast enough rate to make the particles behave as a fluid. Because the beans are completely immersed in the heated air stream, heat is transferred evenly across the surface of the bean, which allows for a consistent, even, and reproducible roast. Many unwanted variables in traditional drum roasting are reduced.

The beans roll over in superheated air, and the unwanted by-products of the roast (burnt chaff, undersize or broken beans, etc) get expelled by the hot air draught. In addition, our fluid roaster comes with forced air cooling outside the roast drum which gives almost instantaneous cooling and allows for the next roast to be in the roast chamber.

As a result, there is less conductive heating, so even when the products do touch the sides of the roast chamber they are gaining significantly less heat from the chamber sides relative to the heat from the bulk air flow. The circulating air removes impurities on the product and results in less tar and carbon buildup (in the case of coffee the chaff, the outer skin of the coffee cherry that comes off during roasting). There is also evidence that without that direct contact on the heat source, the roasted items retain more of their nutritional value and also reduce many digestive issues that result from consuming the impurities from the “traditional” drum roasting method.

As a result, this newer roasting process results in an exceptional coffee-tasting experience for our High Grounds customers!!