January 02, 2019

Staying dry minimises cross-contamination

by Detlef Bunzel, Evonik, Germany

The results of a new study show that using dry additives, rather than liquids in feed, reduces the occurrence of caking and lumping in the mixer and can help prevent cross contamination.

Cross-contamination in the mixing process results from the unintentional carry-over of a substance or ingredient from one batch to the next, produced on the same line. When changing batches, product from the batch that is currently being discharged will remain inside the equipment and be ‘carried over’ into the next batch.

 The problem becomes more obvious when the feed formulation is changed. For example, an additive may be used in a certain batch, but may not be intended to be present in the consecutive batch. Nevertheless, a certain level of this additive may be carried over and contaminate the next batch. Keeping cross-contamination to a minimum is obviously a major issue for feed manufacturers and is an essential part of any quality control programme.

How cross-contamination occurs
Levels of cross-contamination have been found to be higher when liquid feed additives are used, compared to when feed is based on dry ingredients. Conditions in the batch mixer do not favour liquid spraying, partly due to powder incrustations on the nozzles. While the particle size of dry bulk additives is well optimised to blend into feed mash, liquid nutrients, when sprayed into the mixer, lead to an increase of particle size. Any liquid droplet sprayed into a dry powder mix will immediately bind several particles by adhesion, substantially increasing the particle size. Dust and finer particles will bind to the bigger particles.

Under field conditions, the dosing and mixing sequence for dry and liquid additives is rarely optimised for best overall performance. It is often compromised by a too short dry mixing time, overlong spraying time and excessive addition of liquids in the main mixer.

The result of the less-than-optimum conditions is that micro-ingredients accumulate in adherences on the mixer walls. Not only will they be missing in the samples of this batch; when they eventually break loose they will increase the supplementation rate of the following batch.

Read more HERE.

The Global Miller
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