Few instruments can satisfy such tough demands. Those that do quickly pay for themselves many times over. Now that online viscometers capable of accurate, reliable and trouble-free operation are becoming available, food processing companies around the world have been quick to seize the opportunity they offer to monitor and control viscosity in real time. The benefits are such that no processing engineer can afford to ignore them.
The Hydramotion XL7 online viscometer is designed to satisfy the most demanding requirements of the food processing industry. It is a rugged 'fit-and-forget' instrument that has proved its worth in numerous installations around the world, with a clean-in-place solid-rod sensor that presents minimal possibilities of fouling. The instrument has a truly hygienic design, with a crevice-free all-welded 316 stainless steel construction which eliminates the risk of material entrapment or 'dead' spaces where microorganisms could propagate.
The XL7 viscometer can be mounted in any orientation and in any location using any size or type of fitting, including sanitary types such as quick-release tri-clamp, RJT, IDF or DIN. The measurement technique deters material build-up on the sensor but has no effect on the fluid.
Although the XL7 has very high sensitivity, it naturally rejects plant noise and vibration and is unaffected either by fluctuations in flow or the presence of bubbles or solid particles. Factory-calibrated using certified viscosity standards traceable to NIST, the XL7 requires no field calibration. With no moving parts, seals or bearings it is virtually maintenance-free, giving a very low total life-cycle cost.
Outputs include a 4-20mA analogue viscosity signal and a more comprehensive RS232 serial data link for remote monitoring or viscosity control.
Pizza sauce
A team at University College, Dublin compared a number of sensors, including the Hydramotion XL7, while looking for a reliable method of continuously determining the viscosity of pizza sauce during manufacture. The aim was to be able to assess the benefits of online measurement compared with the industry standard offline standards(1).
Sauce viscosity has traditionally been measured using rotational viscometers or consistometers, but the researchers found that these offline techniques were time-consuming and could be subject to a degree of operator influence. Online viscosity measurement offered a number of advantages, including continuous real-time analysis, improved process control and less chance of operator error. Moreover the consequent labour saving helped to reduce costs.
The XL7 online viscometer was installed in the pipeline between the sauce production 'kettle' and the storage vats. Sauce samples were also taken from the vats for offline consistometer measurements, and the results of the various methods were compared for repeatability, variability and stability.
In their report, the researchers concluded that the Hydramotion viscometer gave 'very stable readings and the lowest standard deviation of all the instruments used. The Hydramotion readings gave relatively tight output ranges and had the least inherent variability'.
The XL7 was also 'easily capable of measuring all sauces encountered' and 'was capable of handling the particulates suspended within the pizza sauces. Two sauces were out of specification, and the Hydramotion viscometer was capable of picking out these out-of-spec sauces when this occurred.'
"Once installed, the Hydramotion viscometer required little or no operator input, unlike viscosity readings obtained from the rotational viscometer," the report added. "Subjectivity and errors due to operator variability were removed. The Hydramotion online instrument can easily be integrated into the current process monitoring system."
The dedicated readout unit, which can be located up to 1000 metres from the transducer, provides a 4-20mA analogue signal and serial data output for continuous viscosity monitoring and control, either on a stand-alone basis or integrated into a plant-wide control or SCADA system.
"Unlike the single offline measurement of 'kettle' viscosity, online XL7 viscometer provides 100-200 real-time measurements per batch that can be recorded electronically and independently as part of the batch record."
Milk powder
In another application, the Dairy Products Research Center in Co Cork, Ireland, gave a four-star rating to the Hydramotion online viscometer for its contribution to quality control in the production of milk powder(2). The Hydramotion viscometer was the only one in its class to achieve such a high rating.
Advantages highlighted by the researchers include 'high immunity to plant vibration, ease of cleaning and low maintenance requirements'.
Milk powder is produced by the process of 'spray-drying', where concentrated milk is forced at high pressure through very fine nozzles into a chamber of warm air. This process is widely used in the food and chemicals industries for making products as diverse as baby foods, coffee, soup mixes and dyestuffs. The efficiency of drying is largely determined by the degree of atomisation, which is directly proportional to the viscosity of the feed solution. Thus, the viscosity of the milk at the atomisation step has a crucial effect on the characteristics of the resulting milk powder.
With the Hydramotion viscometer in place, viscosity could be measured continuously in real time, ensuring that changes are immediately detected. Importantly, measurements are unaffected by changes in flow rate or the presence of suspended solids or gases. Installed at the pre-atomiser point, the viscometer offered significantly better control of the atomisation process, leading to reductions in wastage, lower energy consumption and better control of product texture, bulk density and moisture content.
Chocolate
Chocolate is a dispersion of finely-divided sugar, milk protein and cocoa in a continuous fat phase, generally cocoa butter or cocoa butter equivalent. During production, molten chocolate must be cooled in a controlled way in order to promote the formation of small, stable fat crystals, a process known as 'tempering'. Stable cocoa butter crystals provide the right qualities of texture, surface gloss and melting behaviour in the finished product. If the crystals are small enough the chocolate will taste smooth and melt just where it should, in the mouth (at a temperature of about 35°C) but not in the hand (at about 20°C).
The viscosity of melted chocolate depends directly on its fat content and the degree of tempering, so monitoring viscosity gives an immediate window into the production process. With this in mind, a leading UK manufacturer of chocolate products recently installed XL7 online viscometers on pipelines leading to its mixing tanks as part of a global automation project. By continuously monitoring the viscosity of the liquid chocolate its fat content could be adjusted automatically in real time, maintaining product quality and reducing wastage.
Conclusion
As with any other technology, the decision to purchase and install an online viscometer is a matter of balancing the likely rewards against both the initial outlay and the ongoing costs once the device is installed. However, by investing in a reliable low-maintenance system such as the Hydramotion XL7, there are immediate benefits in terms of improved efficiency, increased productivity and enhanced process understanding, while running costs are virtually zero. At the same time, labour and wastage costs can be significantly reduced. All this means that the payback time is usually measured in months rather than years. In fact, some companies have benefited so dramatically from using the XL7 that its installation has become a closely-guarded industrial secret.
For too long, process viscosity measurement has been poorly served by unreliable instruments that are expensive to maintain. Now that industrially robust systems are available, exploiting the clear benefits of online viscosity control has become a realistic option for every food processing professional.
Hydramotion is based in Malton, York, UK. www.hydramotion.com
REFERENCES:
1. Duffy, A P, Cullen, P J & O'Donnell, C P (Department of Agricultural and Food Engineering), In-line viscosity monitoring of pizza sauce manufacture using a vibrational viscometer, in Proceedings of the 30th annual Food Science and Technology Research Conference, UCC, 19-20 September 2000.
2. O'Callaghan, Schulz, O'Donnell et al, Improved Control in Dairy Processing (Online Sensor Control for Milk Powder and Cheese Manufacture), DPRC No. 42, 2001.
