Rotating Disc Column
Innovation in taste technology
The Flavourtech Rotating Disc Column (RDC) is a continuous contacting device for the food and beverage industries. It can be used where well-defined contact times are necessary for the soluble components to be efficiently transferred from within solid particles to a liquid medium.
The RDC allows temperature, pressure and residence time to be controlled precisely to obtain near identical conditions for all parts of the mixture being processed, ensuring consistency in processing and ultimately, contributing to a superior end product.
In contrast to batch tank processing, the RDC’s continuous and automated process means labour, energy and overall production costs are reduced as time is not spent filling and emptying tanks.
Applications of the RDC include:
- High temperature extraction of soluble solids from slurries in the instant coffee industry following the aroma recovery process
- Continuous reaction processes in the food industry where precise temperature and times are required, for example enzymatic reactions
- Continuous mixing of liquid/solid mixtures in the food and beverage industry for obtaining a consistently mixed product prior to feeding to the next step in the process line
Benefits
Production efficiency
The RDC’s unique design ensures the materials flowing through it are maintained in a state of continuous gentle agitation, preventing settling and the formation of static pockets.
Quality control
The risk of over-extraction or under-extraction is greatly reduced as the RDC offers precise control of temperature and residence time during the extraction process.
Retention of natural roasted coffee notes
The highest quality coffee aroma is separated from a continuous flow of coffee slurry in Flavourtech’s Spinning Cone Column (SCC). Use of the RDC allows efficient, high-temperature extraction of the coffee slurry, downstream of the aroma recovery step. The aroma is then added back to the final product efficiently producing a soluble coffee that incorporates authentic roast-and-ground aroma. In this way, it is possible to produce soluble coffee efficiently, and at the same time incorporate authentic roast-and-ground aroma.
Compact design
The RDC is ideal as a continuous feed mixing tank, feeding perfectly-mixed product to the next stage of a process. Typically, mixing is conducted batchwise in stirred tanks, creating variations in the feed material quality and requiring a much larger footprint in the factory.
Case Study
The RDC was initially designed with instant coffee producers in mind. Typically in the coffee industry, flavour is recovered following the high temperature soluble solids extraction process by which point many of coffee’s desirable flavours have already been lost.
Based on Flavourtech’s 20 years of experience in the flavour industry, we know that the best natural aroma comes from processing the raw material directly in our Spinning Cone Column (SCC), prior to the product being subjected to high temperatures. As a result, Flavourtech designed the RDC to allow for high temperature extraction of coffee slurry. In Flavourtech’s extraction process, the coffee slurry is first processed through the SCC to capture the natural fresh roast and ground notes. It is then sent to the RDC for extraction of the soluble solids. This means all the fresh coffee notes are preserved and can be added back later in the process to produce instant coffee that smells and tastes like it was freshly brewed! Coffee manufacturers around the world are realising the cost, quality and production benefits of integrating Flavourtech’s RDC into their production lines. For example, with the RDC, coffee hydrolysis can occur in just 20 minutes, far surpassing the two to three hours typical of current batch extraction cell processing methods.
How it works
The RDC is a continuous extraction device operating in plug flow. Its function is to hold a slurry flow (of solids in liquid) for a specified residence time and at a specified temperature so that the transfer of soluble components from the solid particles to the liquid extract is maximised.
Inside the RDC is a central, vertical drive shaft. Attached to the shaft is a series of rotating discs; between each adjacent pair of rotating discs is a stationary disc, fixed to the column, which has a hole at its centre. Slurry moves up the column following the general path indicated in Figure 1. Rotation is used to keep the solids in suspension; wiping/stirring blades (not shown) attached to the discs assist this function.
Figure 1: Product flow through the RDC
The residence time (that is, the time any portion of the slurry spends in the RDC) is typically in the range of 20-30 minutes. The internal volume of the RDC is determined by the desired product flow rate and holding time and is tailored to customer requirements.
