In the coffee industry, different coffee varieties such as Robusta and Arabica are thermally treated with hot air in roasting machines, such as the NEOTEC type RFB Junior, to separate the seeds from the coffee cherries. Roasting takes place at temperatures of approx. 220°C and, depending on the degree of browning, over a period of 30 seconds. To achieve uniform browning, the coffee beans are constantly circulated with the incoming air in a fluidized bed process.

During the roasting process, on the one hand, the silver skins adhering to the green coffee flake off, and on the other hand, on the basis of the Maillard reaction, the conversion of peptides with reducing sugars from the starch, lipids and proteins to aroma substances and melanoidins takes place.

Once the final product has been obtained, the coffee must be cooled rapidly in order to maintain the quality achieved and to avoid post-roasting. Cooling is achieved, among other things, by a quenching process with water.

In coffee roasting, there are two very different exhaust air streams that need to be cleaned:

• The roasting air, which is up to 250 g hot, has a high odor and VOC load of 800 mg/m³ and a relative humidity of 60%.
• The quench air accumulates in a much larger quantity, has just as many VOCs but significantly less odor and also only 80g temperature, but 100% humidity.

The roasting and quenching air is first cooled down with individual heat exchangers.

A countercurrent scrubber removes water-soluble and odor-bearing particles.

A UV ozone module neutralizes the remaining VOCs in three stages:

• by breaking up long-chain compounds using UV light
• by the formation of ozone, hydroxyl radicals and decomposition products
• by reaction of the released ozone with the released compounds (oxidation)

A downstream activated carbon catalyst neutralizes remaining odors and still free ozone.

The waste heat can be further utilized. The ozone remaining from the UV ozone air purification contributes to keeping the activated carbon filter clean by way of catalysis.

The limit values of the TA Air are complied with.