Measuring malt spirit strength

April 18, 2016  1226  1226   

The first liquid to emerge from the spirit condenser is known as foreshots which contains undesirable methanol or other unwanted low molecular weight compounds. Once the spirit strength reaches the predetermined strength typically 72 -74 %ABV the liquid flow is diverted from the foreshots to the spirit receiver.  The spirit runs to the spirit receiver until the strength drops below a typical value of 62 -64%ABV, the precise switch point will vary depending on the distillery.  Once this switch point has been reached the liquid flow is diverted to the low wine and feints receiver. The distillation carries on until the spirit strength reaches approximately 1%ABV at this point the still is switched off.

Traditionally the samples are measured in the spirit safe by turning a control handle on the front of the safe which opens an internal valve and fills a glass test tube with liquid. The glass tube contains a hydrometer and thermometer which are read by the operator.  The alcohol measurement is corrected back to 20oC using alcohol tables. The safe contains two hydrometers for each spirit still and one for the wash still.

The Canongate DensiCheck TX can be used in conjunction with a control system to ensure consistent and efficient operation of both spirit and wash stills.  The system uses high frequency ultrasonics and temperature to calculate the concentration of the liquid.  The instrument is connected via a flange into a flooded section of the distillate pipeline. The stainless steel sensing element has a large measurement window so is unlikely to be blocked with verdigris deposits from the still or condenser.  The strength indication from the instrument is typically read by the distilleries control system (PLC), using the Modbus serial communications link. The control system will either divert the liquid flow automatically by using a combination of valves or by turning the spout in the spirit safe. 

The instrument provides accurate and consistent process control points to ensure the quality of the spirit.  There is a reduction in the labour cost as the spirit safe does not need tending.  With the current cost of energy it is important that the stills are switched off, before any benefits of spirit collection are out-weighed by the cost of the energy used to produce it.

Installed successfully in over 100 malt whisky stills over the last 15 years, the Canongate DensiCheck TX has proven to be the ideal instrument for on-line alcohol concentration measurement. 

You can contact the author neilmoffat@canongatetechnology.co.uk or visit  www.ct-uk.co.uk