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ESL milk production

ESL treatment

ESL treatment
Four process engineering methods for Extra Shelf Life milk (ESL) treatment are available: direct heating, indirect heating, microfiltration and deep-bed filtration. In the ESL direct heating plant, the product is first regeneratively preheated to 70 °C – 85 °C and then heated to maximum 127 °C by direct steam injection. The milk is held at this temperature for approximately three seconds and is then cooled down to 70 °C - 85 °C in a flash cooler. To ensure the product is well stabilised, aseptic homogenisation is carried out at a temperature of approximately 70 °C. As a result of these extremely short heating and cooling times at a high heating temperature, the direct process offers the advantage of top product quality. Taste tests have shown that from an organoleptic point of view the product is virtually comparable with conventionally pasteurised fresh milk.
For the ESL indirect heating plant, the pre-treatment of the milk corresponds to the process for the ESL direct heating plant. The product is supplied to the ESL indirect heating plant from storage tanks. The milk is first heated to 70 °C by regenerative heat exchange and then specially homogenised. Next, the product is preheated to approximately 105 - 107 °C by regenerative heat transfer and then heated to 124 °C in the heating section. The temperature holding time is approximately two seconds. Special tubular heat exchanger sections have been developed to ensure that the product quality achieved is comparable with the quality of  ESL milk produced by direct steam injection. For the microfiltration process, ceramic membranes with pore sizes of 0.8 µm – 1.4 µm are used. Bacteria removal rates of more than 99.5 % can be achieved.
For the deep-bed filtration process, polypropylene filter cartridges are used. The systems consist of a pre-filter with a nominal pore width of 0.3 µm and a main filter with 0.2 µm. The micro-organisms are retained in the depth of the filter medium. Filtration is carried out at separation temperature. Due to the low pressure drop in the filtration system, no additional pumps are required. No retentate is produced as is in microfiltration. Apart from retentate treatment, the process sequence in the heating plant corresponds to microfiltration processes.


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