In the production of instant (soluble) coffee powder, aroma recovery and off-flavor removal have significant impact on the quality of the end product. This discussion describes the processing steps required to produce premium aroma-rich instant coffee with reduced off-flavors without compromising on extraction yield.
After handling of the green coffee beans, the initial stage in producing coffee extract is roasting and grinding the coffee beans to the optimized particle size distribution for extraction. The size of the Roast and Ground (R&G) particles is the first consideration to achieve efficient aroma recovery. More finely ground R&G particles maximizes aroma extraction and yield, while specially designed percolators are required in order to handle the fine particles without having an unacceptable high pressure drop across the percolators and a high risk of filter blockage. To manage this process challenge, new percolators, such as from SPX, are wider and shorter than conventional percolator designs so that finer particles can be used while limiting the pressure drop. Specially designed top and bottom filters on SPX percolators further enable extended running times and minimize the risk of filter blockage.
To achieve the best extract quality from the extraction process, methods have to be used which can gather and preserve the premium aromas. Therefore prior to commencement of the extraction process, steam stripping of aromas from the roast and ground coffee recovers the most volatile and desirable aromas. The resulting aroma-rich steam is condensed and stored under chilled conditions to be added back into the extract prior to coffee extract standardization.
Once the most volatile aromas have been stripped using the steam, the coffee extract quality is further enhanced by using low-temperature, lenient extraction conditions. The primary, aroma-rich extract this produces is stored with the aromas recovered from the steam stripping.
A second high-temperature extraction stage takes place to obtain high yield, hydrolyzed extract. This stage of aroma extraction forms undesirable off-flavors which, are removed to maintain premium extract quality. The undesirable off-flavors are removed by flash separation in a vacuum vessel. The secondary hydrolyzed extract is then cleaned in a centrifuge to remove sediments and subsequently concentrated in an evaporator.
Steam stripping of aromas followed by the low-temperature and then high-temperature extraction conditions (known as dual-dual extraction) helps to ensure the primary aromas are preserved while still maintaining high extraction yield. Once the hydrolyzed extract has been concentrated, the premium aromas are added in-line to the concentrated extract to obtain the desired aroma quality in the extract. Due to the high viscosity of the concentrated coffee extract, using an in-line mixer at this stage can achieve good homogeneous mixing compared to mixing within the tank.
Dr. Masters is regional sales manager at SPX Flow Technology, Food and Beverage Division (coffee). Niesse is sales director at SPX Flow Technology, Food and Beverage Division (coffee), and can be reached at [email protected].