High shear mixing for food applications
For over 75 years, Silverson Machines has been supplying customers large and small across the world with high-shear mixing equipment. In our cover story this month, we explore some of the mixing tasks Silverson mixers can be used for and how this can be advantageous to manufacturers in the food industry.
With its extensive knowledge and expertise of applications in the food industry, as well as the versatility of Silverson mixing equipment and the size of the product range, the company has supplied mixers for hundreds of food applications.
Many of the most common applications that Silverson provides mixing solutions for now have their own ‘how to’ video on the Silverson website. These videos demonstrate how a Silverson high-shear mixer can be beneficial in applications as diverse as preparing samples for aflatoxin testing, manufacturing agglomerate-free batter mixes, or effectively dispersing gums and thickening agents, such as pectin or xanthan gum, for better quality products.
Deagglomerating gums and thickeners
One of the most common problems when dispersing powders, such as gums and thickeners, into liquid is the formation of agglomerates. If not dispersed correctly, these agglomerates can affect the appearance, texture and quality of a finished product.
When agglomerates remain in a mix, this results in a low yield of the powdered ingredients, leading to increased processing costs, and often, a filtration stage is needed to remove the agglomerate, adding extra time to the process.
By using high shear when mixing powdered ingredients into water, agglomerates are instantaneously broken down as they pass through the rotor/stator workhead, resulting in an agglomerate-free mix with maximum yield.
One food manufacturer got in touch with Silverson for help revitalising its mixing process after their previous mixing set-up became too expensive due to the high percentage of pectin in its formulation. The customer had been using a conventional agitator to try and disperse the pectin, but agglomerates kept forming in the mix. Because of this, the customer had to incorporate much more pectin than they needed to obtain their desired results.
After seeing the Silverson’ how to’ video on dispersing pectin, they got in touch, and a trial was run using a Flashmix powder/liquid mixer. Using the Flashmix, 5% pectin was quickly incorporated into the liquid stream via the powder hopper. After a short recirculation period, hydration was complete, and the customer got the results it wanted with no need to add excess amounts of powder.
Incorporating 5% pectin quickly and effectively meant a 20% reduction in pectin compared to the previous process. The cost implications of this were huge, so much so that the mixer would pay for itself many times over with the savings made on the raw material. In addition, further money would be saved due to the shorter processing time, and because it eliminated the problems with partially hydrated pectin in the vessel, greatly improved process hygiene.
Reclaiming waste
High shear mixing has long been used for the reclamation of confectionery, with the high cost of raw materials such as sugar and cocoa encouraging manufacturers to reclaim and rework ‘off-spec’ product. But now, this is expanding into other areas of the food production industry with cheaper processing costs, for example bakery products and waste pasta, as manufacturers aim to become more sustainable in their processes. The reclamation of these products works in a similar way to reclaiming confectionery; the product for rework is incorporated into a liquid, usually water, and reduced down into a slurry. This slurry can then be used in subsequent batches of the product. For this process to be effective, the mixing equipment must be capable of disintegrating solid material down into a homogeneous mixture, which can be forwarded on for further processing.
The clarification and recycling of vegetable oil waste is another innovative way in which the food industry is trying to combat excessive wastage. In a recent case, a Silverson customer wanted to manage the amount of oil it was using by prolonging the usable life of vegetable oil, with the goal of eventually reducing the wastage to zero. The vegetable oil, which was being used in the batch frying process for a snack product, could be reused by incorporating a food-grade powder, which would reduce the free fatty acid levels to below a threshold where it would then be suitable for reuse. An impeller was unable to prevent a thick residue from building up in the vessel due to the limited movement it was creating in the tank, and this was affecting the ‘cleaning’ of the oil. The in-tank movement created using a high-shear mixer kept the product recirculating throughout the entire vessel while incorporating the powder. Once a high-shear mixer was incorporated into its process line, the amount of new oil being purchased by the company was reduced from 30,000 litres every week to 30,000 litres every two weeks, cutting their processing costs by 50%.
Homogenisation
A Silverson high-shear mixer/homogeniser can achieve a globule or droplet size of 2 – 5 microns. In some cases, depending on the formulation, finer results down to 0.5 microns can also be obtained, eliminating the need for expensive homogenisation equipment in the manufacturing process.
This is what happened recently when a flavouring manufacturer purchased a Silverson Batch mixer after successful trial results at a laboratory scale. Before contacting Silverson, the company was using a process that relied on mixing ingredients for a long time using a conventional agitator to form a pre-mix. This pre-mix was then fed through a high-pressure homogeniser several times to obtain a uniform particle size of 5 microns.
After seeing the Silverson Mixing Science ‘What is homogenisation’ animation on the Silverson website, the company got in touch to find out what particle size it could achieve using a Silverson High Shear mixer. A trial was arranged to test the company’s application at a laboratory scale.
For the trial, a Silverson Laboratory mixer fitted with a General Purpose Disintegrating Head was used. Keeping the ingredients and formulation the same as its current process, when using the Silverson Laboratory mixer, the company was able to achieve a uniform particle size of around 1.5 microns after only five minutes of mixing. This was a huge reduction in processing time compared to the previous mixer, and the particle size had been reduced finely and uniformly enough that they could completely eliminate the high-pressure homogenising step.
The company immediately scaled up and purchased a Batch mixer, which has been added to the process line and has been able to produce high-quality flavouring for them in a much quicker time. In most cases, the company now bypasses the high-pressure homogenisation stage, but when used, the pre-mix created with the Batch mixer means it passes through at a much faster rate and in a single pass.
Forming stable emulsions
In order to form a stable emulsion, whether you are producing an oil-in-water or water-in-oil emulsion, you need to obtain the finest possible droplet size. The mixing equipment needs to impart a large amount of energy into the mix; the more shear energy introduced into the mix, the smaller the suspended droplets will become, creating a fine, stable emulsion with both phases completely and uniformly dispersed into one another.
Conventional mixers and agitators, which are suitable for basic liquid/liquid blending, are unable to form a stable emulsion because they do not have the necessary means to impart large amounts of energy into the mix. This type of mixing equipment simply moves the two liquid phases around the vessel, so although it may appear as though the phases have blended, the droplet size hasn’t been significantly reduced, so once the agitation stops, the emulsion will soon separate into the two distinct phases once more.
High shear mixing subjects the liquids to intense high energy, which reduces the droplet size sufficiently and allows the two phases to combine, resulting in a stable emulsion that will not separate once the shear energy has been removed.
As well as the above mixing tasks, a single Silverson high shear mixer is also able to perform a wide range of other mixing processes, such as dissolving, reducing particle size and blending liquids of varying viscosities, with speed, consistency and substantially reduced mixing times compared to conventional mixing equipment.
