: Figure 1. Frozen pizza before and after homogenisation.

: Figure 2. The optimal conditions for homogenisation of food are not necessarily at the maximum speeds of the grinder. The above images of the homogenisation of apples show that when they are ground at 1000 rpm (centre image), the result is less «mushy» and therefore easier to analyse than when they are ground at 3500 rpm ( right image) .

Foodstuffs occur in many different forms and consistencies, and are not usually homogeneous. To obtain meaningful and reliable analytical results, the samples to be tested have to be homogeneous and representative.
A new grinding mill is ideal for such applications.

Allowing processing of larger samples than the well-established Grindomix GM 200 grinding mill, the newly developed GM 300 allows samples of up to 4.5 litres to be homogenised quickly and reproducibly. Meeting all special laboratory and analytical requirements, the new grinding mill processes substances with a high water, oil or fat content as quickly and reliably as dry, soft, medium-hard and fibrous products. This makes the instrument far superior to any commercial household mixer.

The grinding mill is suitable for a wide range of food materials including fruit, vegetables, sausages, meat, fish, cheese, ham or frozen food as well as feed pellets, spices and seeds. The special knife and the variable grinding chamber allow for the quick and easy processing of these products into samples suitable for analysis. A great advantage of the grinding mill is that retail quantities (such as 800 g frozen chips or a loaf of bread) can be ground and homogenised as a single sample.

GM 300 technology
Four sharp, robust blades rotate in the centre of the grinding container. Depending on the rotational direction, size reduction is effected with the blunt side (preliminary size reduction) or the sharp side (fine grinding). The knives are protected from damage by hard sample materials with a counterblade. The knife is indirectly driven by a powerful industrial motor of 1,100 W, which can reach temporary peaks of 2,500 W.
The mill was designed with a special focus on simple and convenient operation. The handling is exceptionally comfortable and safe, and the grinding container and knife are easily attached without the use of tools. When the preset grinding time has been completed, the motor automatically stops and the grinding container can be removed. Thus unlike with household mixers, the container can be filled and emptied away from the mill. This makes cleaning very simple and helps to avoid cross-contamination. In addition all components of the grinding mill that come into contact with the sample material are autoclaveable. The instrument can be adjusted for a great variety of applications.The speed is adjustable in increments of 100 rpm and ranges from 500 to 5,000 rpm. The grinding time can be set from 5 seconds to 3 minutes. Speed and grinding time are indicated in the digital display. Up to 10 parameter settings can be stored, facilitating reproducible grinding, and allowing different speed and time combinations to be run successively. Interval and reverse modes can be used to improve the results with tough elastic products, or for preliminary size reduction.

Homogenising frozen food
Frozen foods can be introduced into the mill without prior defrosting. Homogenisation is completed within 30 seconds at 3,500 rpm [Figure 1].

Homogenising fruit
Operation of the mill at full speed is not always to be recommended because this can lead to undesirable side effects. If fruit is homogenised at high speed, it loses cellular water and becomes mushy, which makes it difficult to handle in subsequent analyses. The rotational speed of the knifes can however be varied to suit the application. The example of grinding apples clearly shows how much the results depend on the selected speed [Figure 2]. Most of the samples prepared in the instrument are completely homogeneous after a few seconds of grinding, thus facilitating reproducible results on analysis. A great advantage of the mill is that not only is it very powerful, but that it also enables the more gentle grinding conditions suitable for fruit.

Retsch GmbH
Haan, Germany

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