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Process and Product Integrity in Yogurt Production at Danone

Service Life of Sterile Filters Extended

Industry: Yogurt production

Problem: Sterile filters, which are used in the Danone plant, have to meet the high requirements of the food and beverage industry and also be effective under extreme operating conditions.

Solution: The new Donaldson sterile filters allow for a considerable extension of the filters' service life, while keeping high retention rates – leading to significant cost savings.


Yogurt and dessert products are of particular importance to the dairy industry. In Germany, annual yogurt consumption per capita in 2016 was 16.8 kg / 37 lbs(1). ACTIVIA by Danone is one of the best-known yogurt brands. Production in the Ochsenfurt am Main plant in Germany is carried out under stringent conditions governing product integrity, involving filtration as one of the key technologies in the biotechnological process sequence. A new series for the sterile filtration of compressed air ensures a high degree of process reliability. This innovative development also brings with it an economic factor of particular significance: filter service life is considerably extended.

(P)-SRF C pleated sterile air depth filter

In the spring of 2017, the Research and Development division at Donaldson in Haan/Germany was able to report the successful conclusion of a long series of tests with sterile filters for compressed air, fermentation air, carbon dioxide and other process gases. They had been able to significantly extend the service life of the (P)-SRF sterile filter series while still guaranteeing the high retention rate, which is crucial for the integrity of product and process. This success was possible with their use of the latest filter media, which had undergone innovative processing and optimization of mechanical and thermal stability. As a result, requests from customers, higher quality standards worldwide in production and management guidelines relating to greater safety, sustainability and innovation were all met.

For Thomas Karollus, Consulting Engineer at Donaldson for process filters, the next step was obvious – he wanted to show Danone the new filters and recommend that the company compare them with the previous series by using them in practice. The mutual trust that has developed over almost 20 years between filter specialists at Donaldson and Danone in Ochsenfurt made for a quick decision. Since July of 2017, the previous (P)-SRF and (P)-SRF N filter elements have been gradually replaced by the new sterile filters of the (P)-SRF C (C = compressed air) series.

Filter system in the tank room
The new sterile filters at the Danone plant in Ochsenfurt...

The (P)-SRF C sterile filter meets the high require­ments of both the food and beverage industry and the pharmaceutical industry, and is also effective under extreme opera­ting conditions. The (P)-SRF C filter element is a pleated depth filter with inner and outer support linner and end cap­s made from stainless steel. The borosilicate filter media is impregnated with PTFE and is equipped with PTFE exterior protective fabric. The retention rate is > 99.99999995% based on 0.2 microns and > 99.99999995% based on 0.02 microns. For nanoscale particles (0.003 microns), retention is > 99.999999991%, which has been ver­ified on the basis of DIN EN 1822.

All components meet the requirements for indirect contact with foodstuffs in accordance with the CFR (Code of Federal Regulations) Title 21 and Regulation (EC) No. 1935/2004. No chemical additives are used in the manufacture of the fil­ter medium. The robust design allows for more than 160 sterili­zation cycles at 141° C / 290° F in both flow directions and also enables the use of other sterilization methods, such as ozone or VPHP.

... and their significance for production

The significance of these sterile air filters becomes clear when considering the process sequence involved in yogurt production:

The fat and protein content of the delivered fresh milk is adjusted, and the milk stirred vigorously enough for the fat beads to shatter into smaller particles and disperse evenly. During the subsequent pasteurization process, it is heated to 90-95° C / 194-203° F for a few minutes before being cooled to 40° C / 104° F. Fermentation is performed with a special mixture of five bacterial strains.

Thomas Karollus, Sales Engineer at Donaldson, explains the filtration technology in the tank room. The (P)-SRF C sterile filter ensures high retention rates and a long service life.

The mix is fermented in a tank whose temperature is kept constant at 37° C / 99° F for a period of eight hours. During this time, the milk acidifies and gradually thickens. During this process step, the mix is gently stirred to maintain a smooth consistency. It is then cooled to 20° C / 68° F for two hours in order to reduce the activity of the ferment. The mix is then decanted into cups or bottles and finally cooled to 4°C/39°F to ensure that the cultures remain intact.(2)

The tanks are emptied by pressuring them with high-purity, sterile compressed air.; this is where the filtration technology comes into play. The compressed air produced and dried in the central compressed air station is reduced to approximately 2 bar, with the (P)-SRF C sterile filter ensuring that this air is sterile and free of any particles. The high retention rate of bacteria, viruses, and particles up to ≥ 3 nm (nano­meters) supports product and process integrity.

Since the introduction of the new (P)-SRF C sterile filters, their use under a wide range of operating conditions in the food and pharmaceutical industries has shown that more than 160 sterilization cycles are achieved. This applies, for example, to the 20-minute sterilization in both flow directions with 131° C / 268° F saturated steam. The replacement interval recommended by Donaldson is 12 months.

(P)-GSL N steam filter – close-up of the stainless steel fiber web
Sterilization of filters with saturated steam

At Danone, filters are sterilized with saturated steam, which must meet equally high purity standards, and is filtered using the Donaldson steam filter elements of the (P)-GS/(P)-GS VE and (P)-GSL N series. The high steam quality contributes to the extended service life of filters that require sterilization, thereby making the entire process more cost-effective. Another feature of the new (P)-SRF C sterile filter relates to its excellent drying characteristics. Blow-drying, and the immediate return to low differential pressures after steam sterilization, is completed within a few seconds. Downtimes, energy consumption and mechanical stresses on the filter medium are significantly reduced as a result.

The cooperation between Danone and Donaldson demonstrates how significant improvements with substantial economic benefit can be achieved by making small changes. This is completely in keeping with Donaldson's corporate aims and objectives: Safety – Sustainability – Innovation.

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(1) Source: MIV/molkerei industrie
(2) Source: –
Important Notice 
Many factors beyond the control of Donaldson can affect the use and performance of Donaldson products in a particular application, including the conditions under which the product is used. Since these factors are uniquely within the user’s knowledge and control, it is essential the user evaluate the products to determine whether the product is fit for the particular purpose and suitable for the user’s application. All products, product specifications, availability and data are subject to change without notice, and may vary by region or country.