Analytical Instrumentation & Environmental Monitoring

Optimising ESL milk standardisation

August 2015 Analytical Instrumentation & Environmental Monitoring

Although the process steps involved in the production of drinking and extended shelf life (ESL) milk are different, fat standardisation is generally still taken care of indirectly in both cases using Coriolis flowmeters. A new method of fat standardisation using a non-contact, inline analysis device capable of measuring the fat content in ESL milk with extreme accuracy is introduced here.

The basics of milk production

To produce drinking milk with various minimum fat contents, the raw milk is separated in the dairy into skim milk (approx. 0,05% fat content) and cream. The Coriolis flowmeter is placed in the flow of cream to measure the fat content. In addition to measuring the direct mass flow, Coriolis flowmeters also measure the density of the product. The fat value is calculated using this density and a fixed formula.

However, the only reason this fat measurement is relatively accurate is because the fat content in the cream flow is sufficiently high. Measurements done in the drinking milk, where producers would actually like to measure the value, are not nearly accurate enough to regulate the fat content.

Using the current flow rates of skim milk and cream, it is possible to calculate how much cream must be added to achieve the desired fat content in the standardised milk. In addition to the inaccuracies of the measuring and final controlling devices, the approximate 0,02% fluctuation range of the fat value in skim milk plays a role when it comes to customer requirements for high accuracy. Consider also the many process steps involved in ESL milk production, whereby partial flows can be pasteurised, homogenised and micro filtered, it is easy to see why the inline measurement of fat content is advantageous.

Taking into account the various uncertainties regarding indirect fat standardisation, the real fat value must be regularly checked by way of sampling and laboratory measurements. These tests take a relatively long time in the laboratory, meaning intervention in the process is thus correspondingly delayed. In the case of deviations from the required fat content, the target value is manually changed and more or less cream is added accordingly.

Spectroscopic analysis simplifies the process

Krohne’s new Optiquad M is a spectroscopic analysis system well suited to the task of fat standardisation, as it performs continuous inline non-contact measurement of fat content directly in the drinking milk. In addition, it also measures the protein and lactose content in milk products. The Ammerland dairy processes approximately 3,3 million litres of raw milk per day and was looking for a solution to the problem of fat standardisation in ESL milk. Particular emphasis was placed on continuous accurate measurement to enable improved process control without time delay. The dairy installed an Optiquad M 4050 W. The analyser unit was installed directly in the production line by way of a standard Varinline process connection without bypass. This entire measuring section fulfils the high hygienic requirements and is FDA-compliant.

The analyser unit contains no moving parts, and the wetted parts are cleaned via CIP. The operating unit, built in a stainless steel housing, is installed in close proximity to the analyser and connected using a serial interface. Its purpose is to display the measurements, make them available to the control unit via 4-20 mA outputs and enable all entries and actions. To this end, the operating unit is fitted with a modern industrial PC featuring touchscreen operation.

The operating unit also takes care of any required optimisation of calibration. To do so, samples are first taken by way of the integrated sampling valve. During sampling, a button is activated to notify the analyser unit and the measurement, determined over the entire period of sampling, is saved in the operating unit. The reference value as determined in the laboratory is then entered. If several samples have been measured and entered, the current calibration can be optimised at the touch of a button.

The measurements of the Optiquad M were recorded over several months. The accuracy was found to be in the range of the reference measurements determined in-house and in independent laboratories. “Our confidence in the device grew when we heard this,” commented dairy production manager, Armin Tjards. “With Krohne’s solution we can measure the fat and protein content directly in the standardised ESL milk, in other words, exactly where we want to measure. We can now continuously look into the process which means that we were able to set the desired fat content precisely, even in the complex production processes of ESL milk.

Optiquad M functionality:

The analysis system uses optical spectroscopy to measure the contents of milk products continuously and without contact. In the process, light of varying wavelengths is coupled into the product through an optical window. The system simultaneously determines the values of up to four optical effects (transmission, scattering, fluorescence and refraction) which manifest in different ways depending on the substances in the product, and then uses them to calculate the amounts of protein, fat and lactose.

For more information contact John Alexander, Krohne SA, +27 (0)11 314 1391,,


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