Rheology Solutions on QC measurements for liquid food products and packaging:
Production quality and uniformity in food processing and its subsequent packaging is closely related to good quality control (QC) during the manufacturing process.
In order to achieve high quality merchandise with minimal production losses, good process control and monitoring is critical.
This is true for production of both the food product itself, the packaging and of course for putting the former inside the latter efficiently.
Laboratory and on-line systems are capable of delivering solutions for QC monitoring and in cases where extra information (related sometimes to product development and not to QC) about the flow properties are unnecessary, an online option can be the most useful.
On-line systems often provide streamlined data, showing changes in more limited criteria for the product during the process. In this way corrective action can be quickly taken, minimising potential for waste and reprocessing.
Laboratory instruments, designed for quick data collection (only a few seconds or minutes) and intuitive understanding of the data can also be useful in this respect where no proven online alternative exists.
On-line monitoring of shear viscosity is widely accepted for many kinds of materials including for liquid foods and molten polymer packaging. In pipe or in-tank probes can closely monitor the shear viscosity of the material in-situ, allowing operators and engineers to take appropriate action to maintain the specifications of the food product.
These probes can also be mounted at the die end of an extruder, to monitor the viscosity of molten polymer before the moulding of packaging.
Post-extrusion, the quality of the packaging material can be monitored optically to detect, catalogue and notify when user defined flaws exist in the packaging material (eg. fish eyes, pinholes, dark/light spots etc).
For filling a liquid food into a package (by pouring, squirting, spraying etc), extensional viscosity often dominates the process.
Unfortunately, there is no proven on-line method for monitoring the extensional viscosity of foods as they are dispensed from above into their packaging.
Fortunately a novel, simple and quick laboratory technique has been developed for exactly this purpose – measuring the relative impact of the extensional properties of a liquid.
In this way the product and the packaging can be monitored on-line right through the process, until the product has safely been deposited in its packaging.
Introduction
Several products exist today for testing in the laboratory, both for QA and for product development.
Laboratory testing for product quality in the food industry can include rheometers and viscometers, to measure liquid flow properties such as yield stress, viscosity and elasticity under different shear flow conditions.
These instruments can also measure the flow properties of packaging materials, eg molten plastics etc, to ensure that they can be properly moulded etc.
Testing of solid like properties in the laboratory is possible for both foods and their packaging with uniaxial testing. Miniature uniaxial testers – texture analysers – can be used to objectively quantify textural properties of a food, while units with larger capacities can also be used to investigate the tearing, stretching, crushing etc of the finished packaging product. Often, during filling, a liquid is poured, squirted, sprayed or otherwise dispensed into the package.
For some materials stringy strands hang from the nozzle and soil the packaging, necessitating an extra process step to clean the packaging.
This stranding is related to the extensional viscosity of the material (completely different to the shear viscosity measured by rotational viscometers). Recently developed techniques now enable these extensional properties to be properly measured in the laboratory using extensional rheometers.
Laboratory analyses are good solutions for material characterisation and in many cases can not be otherwise replicated online.
However, during production it is sometimes preferable to have an on-line system for QC, so that any deficiencies in the product or its packaging can be detected as quickly as possible.
This technical note seeks to explore and to explain on-line viscosity monitoring, online quality control for packaging film and ingredients and a novel laboratory technique for monitoring the extensional properties of liquids to diagnose excessive stranding.