How High Shear mixing can help improve your Tomato Ketchups


High Shear Rotor/Stator mixers are widely used in the manufacture of sauces such as salad cream and mayonnaise, and they can play a vital role in the manufacture of ketchups. 

Using high shear mixing technology to manufacture ketchup can help to eliminate some of the more common problems associated with the mixing process.  It can also enable manufacturers to achieve better product quality and maximised yield with shorter mixing times. In some cases, it can even eliminate the need for the high pressure homogenisation step.

Tomato ketchups are made by mixing concentrated tomato paste with other ingredients. Diluting the tomato paste into water is one of the first stages of the process. This can be difficult when using conventional mixing equipment, due to the differences in viscosity. The more viscous paste tends to form globules that don’t readily blend with the surrounding liquid. This is known as stratification. Once these globules have formed, agitators and stirrers do not produce the shear necessary to disperse them, leaving them undiluted in the mix.

More problems can occur when incorporating additional ingredients such as thickening agents. Pectin or starch (including modified starches) are often used in tomato ketchups to obtain the required viscosity in the finished product.  These ingredients can cause problems for conventional mixers as they cannot easily disperse or hydrate them. As the thickening agents are supplied in powdered form, these tend to form agglomerates when added to liquids; once these have formed the agitator does not produce the necessary shear to ‘break into’ the gelled outer surface of the agglomerate and disperse the dry powder inside. The agglomerated ingredients can remain in the mix, reducing the yield of thickening effect and increasing processing time, as a filtration stage would be necessary before subsequent processing.

So how can using high shear mixing equipment help to solve these problems?

The positive mixing provided by a Silverson machines blends the ingredients instantaneously. The intense shear energy created by the high speed rotor draws materials into the workhead where they are intensively mixed. Centrifugal force then drives the materials to the periphery of the workhead where they are sheared in the gap between the rotor and stator, breaking up any lumps that may have formed and eliminating agglomerates from the mix. The continuous mixing cycle created by the high shear mixer progressively reduces globule or particle size and quickly results in a homogeneous, uniform product. This maximises the yield of the raw ingredients and improves the quality of the finished ketchup.

With some manufacturing processes the premixed raw materials are passed through a high pressure homogeniser. This activates the thickening effect of the pectin found naturally in tomatoes, giving the ketchup the desired viscosity. But for this to work effectively the homogeniser must be fed with a uniform pre-mix. If undiluted or incorrectly dispersed ingredients remain in the mix or if the globule size is large or uneven, several passes through the homogeniser may be required and throughput can be low, leading to long and costly processing times. A pre-mix created with a high shear mixer will be of a uniform, low globule size, allowing faster processing through the homogeniser and fewer passes required, a major saving in processing times.

Some formulations of ketchup with low solids content do not actually require high pressure homogenisation. The entire process can be completed with a Silverson high shear mixer. High shear enables the mixer to blend the tomato paste and hydrate and disperse the thickening ingredients to achieve the desired viscosity. It can also reduce particles size down to the 2 – 5 microns. The precision-machined Silverson workhead generates exceptionally high shear rates in a three stage mixing/homogenising process; The high speed rotor draws materials into the workhead where they are intensely mixed. Centrifugal force then drives the materials to the periphery of the workhead and subjects them to mechanical shear in the precision gap between the rotor and stator. This is followed by intense hydraulic shear, as the product is forced through the stator screen at high velocity and circulated back into the mix. Fresh material is continually drawn into the workhead, progressively reducing globule or particle size and quickly resulting in a homogeneous, uniform product.

Homogeneous particle sizes in the range of 2 – 5 microns (smaller depending on the formulation) are suitable for other sauces such as Mayonnaise, Hummus and salad dressings, allowing one high shear mixer to be used for several products.

If you’d like to find out more about how high shear mixing can be used for the manufacture of tomato ketchups, or other sauces, please visit the Silverson website.



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