Homogenization

Homogenization of a product is often necessary to stabilize the fat in the product or enhance the mouth feel. The smaller the particle size and the fat globule size the smoother the mouth feel.

Small fat globules also improve the shelf-life of the product since smaller fat globules have a lesser tendency to float.

Homogenization is not often a fully understood process. Unfortunately wrong pressure and/or wrong homogenization temperature is chosen. See the diagram underneath where the pressure was the same but the homogenization temperature was changed.

This diagram can also be translated:  If the right temperature is chosen, the pressure can be set lower. The advantages are clear, of course.  But, sometimes it happens that fat globules are damaged during the homogenization. This happens most often when the temperature is too low or the pressure too high. When fat globules are damaged they have the tendency to join, thus increasing in size and then rise to float on top of the product.

Damaging can also occur if the piston chamber is not filled fast enough. This could happen if the product- supply pump is under dimensioned. The pressure build-up in the piston chamber will not be built-up smoothly (it should be according as to a sinus function) but abruptly and, therefore, creating pressure spikes in the piston chamber and, therefore, spikes in the homogenization pressure.

Homogenization damage can be done according to the following principles:

Hammering is created when two or more metal objects are slammed together while the product passes in between.

Sudden speed change is often created to force the product through an extreme narrow gap. 3 - 10 micrometer. In this gap the speed of the product can increase to over the 225 meters per second. This sudden speed change will shear the fat globules apart in multiple small globules. Sudden speed change can also be created / simulated by sudden change of direction of the product (cavitation and micro- turbulence). Since fat has a different mass then the other ingredients in the product, sudden changes in direction will create micro-turbulence and shear, which will tear the fat globule to smaller globules.

A combination of both is also possible and a lot of homogenization valves are unfortunately working accordingly. Although not admitted by the manufacturer, wrongly designed homogenization valves or badly filled piston chambers will let the homo valve vibrate on its seat and create this effect. In a particle size analyzer, the results will look very promising but after some time the fat globules will reunite and start to float.

Homogenization can be done in one or multiple steps.  For most, step 2 is sufficient.  It is common that the main homogenization takes place in the first homogenization valve and a mild homogenization in the second valve.  A  1 to 4 factor is often used. The second homogenization valve will enhance the product's quality. It will break down the newly formed fat globule clusters formed directly after the first valve (re-agglomeration) . If the first valve is before the main heater and the second valve after the main heater it will also break down the fat-globule clustering which took place in the main heater and holding tube. Due to this, it is often said that homogenization should only take place after the main heater. There is a lot to say for this statement,  but it can also give micro-organism problems when UHT processes are used. It can be imagined that non-homogenized products can contain "big" particles and fat globules. It is reasonable to assume that the holding-tube time is too small to let the heat penetrate into the center of the particle, which results in a too-low effective lethality. This problem will surface for example with coco containing products. 

Last modified: Monday, January 17, 2005 14:51:40    1999-2005 Copy right © ASEP-TECH USA LLC. ALL RIGHTS RESERVED.