Protein Shifting

Important resources and economic utilisation of vegetable proteins and starch from legumes

With a jointly developed innovation by the companies F.H. SCHULE Mühlenbau GmbH, HOSOKAWA Alpine AG and AMANDUS Kahl GmbH & Co. KG high-quality vegetable protein and starch concentrates are produced. Vegetable proteins are extracted from quickly reproducing and inexpensive starch-containing legumes.

Proteins are getting more and more important for the human food and animal feed industry. This increasing demand is a result of the exhaustion of natural resources, the rise in population as well as changing eating habits.

1. General information on protein shifting

Legumes such as peas and beans, for example, are decomposed into highly enriched starch and a highly enriched protein fraction.

Protein fraction:

Until now, mainly animal proteins have been used in the concentrate sector. Prices, however, are dramatically increasing. In the year 2007 alone, there was a price increase of more than 25 % for fish meal. This affects also wild fish stocks, which are in danger of extinction around the world. Thus, every alternative to animal proteins is considered a great opportunity.

Composition of a feed:

(Figure 1)

The importance of protein resources becomes evident when considering the fish industry with its increasing number of fish farms which are typical of common industrial animal husbandry. Protein is supplied to the feed mainly by means of fish meal obtained from wild fish stocks. The balance shows that 5 kg of wild fish are needed in order to produce 1 kg of fish on fish farms! (Powell K. (2003), Nature 426, 378-379).

The protein concentrate is not only used for various feed formulae in the fish, poultry and rearing feed industry. It is of particular interest in the convenience food industry, where protein concentrates are used to increase the nutritional value.

Starch fraction:

Due to fractionation of the product, starch concentrate is obtained as another valuable component. Apart from its use as an additive to fattening feed with a low fibre content, the properties of starch with a relatively high amylose content, like that of peas for example, can be benefited from by the food industry. The starch concentrate can be furthermore used in the sweets industry (where high-quality starch from starch factories is not always required) and in the paper industry or for the production of biodegradable bioplastics.

Another important application of starch concentrate is the production of bioethanol. Due to the reduced fibre content, this fraction with its reduced water absorption is an efficient raw material. The particle size allows a faster and more intensive fermentation, which ensures a pure alcohol yield which is by 32 % higher than that of wheat.

2. The precision process of protein shifting by the companies Schule, Hosokawa and Kahl

The optimised precision process could only be achieved by means of common research & development work of the companies F.H. SCHULE Mühlenbau, HOSOKAWA Alpine and AMANDUS Kahl. The required optimum shelling degree is precisely adjusted in the Schule shelling process. This process ensures a four times higher service life of the shelling tools compared to alternative machines available on the market. This increases the service life of the grinding tools in the fine grinding section by about 10 times. For pelleting of the three fractions, protein, starch and shells, the proportioning and pelleting process has been optimised.

This precision process integrates the different processes.

Results of the precision process:


Peas (Pisum sativum)

Field bean (Vicia faba)

Protein concentrate:



Produced quantity

up to 35%

up to 40%

Protein content (fines)

up to 55%

up to 65%

Starch concentrate:



Produced quantity

up to 65%

up to 60%

Starch content (coarse product)

up to 75%

up to 70%

a. Schule cleaning and separation process:

Protein shifting starts with cleaning, separation and shelling of the products.

The high-molecular fraction of the seed coat which serves as a protection of the endosperm (tissue inside the seed pod) is difficult to grind in the following fine grinding section. Therefore, the energy demand for grinding the seed coat consisting of cellulose, lignin and pectin is significantly higher than for the other components of the endosperm.

The process capacity is reduced to up to 50 % if peas or beans are fed into the grinding process which have not been optimally shelled.

After the product has been cleaned by means of the SCHULE cleaning machine, an efficient classification is required. The classification process makes use of the physical properties of the grains. When processing peas, it is important to process peas of the same colour (yellow or green). The raw material mainly consists of approx. 50 % of yellow and 50 % of green peas. After physical classification they are separated into a yellow and a green fraction by means of colour sorting. (Figure 2)

Sorting the products according to their colour is important for different reasons. On the one hand, the grinding properties of yellow and green peas are different and on the other hand, the colours of the individual concentrates change as follows:

Yellow peas:

creamy yellow protein

white starch

Green peas:

white protein

greenish starch

b. Schule shelling process:

The new concept of the Schule conical shelling machine Verticone VPC ensures a controlled shelling process of cereals which is linearly adjustable.

Due to the special features of the shelling machine, a separation of endosperm and shell is possible with a lower fines content than in other systems, which increases the yield of the fractions. (Figure 3)

Capacity of the Verticone:

  • up to 15 t/h
  • drive power of up to 90 kW, compatible with PLC 

Via a screw installed in the inlet the product is fed into the shelling chamber. This chamber consists of a conical sieve drum and abrasive conical grinding discs or a shelling rotor with air channels. The smaller diameter of the shelling rotor is right below the feeding screw, the bigger one directly above the outlet.

Below the shelling chamber, there is an outlet ring which keeps the product in the shelling chamber.

The adjustable shelling gap (between shelling rotor and sieve drum) of this machine allows an optimum adaptation to the different product sizes as well a modification of the shelling degree, for example by changing the counterpressure of the outlet ring. The shelling degree can be influenced further by the throughput and the counterpressure.

If this is desired, this process ensures the complete removal of the seed coat.

c. Hosokawa Alpine air classification mill:

The product is continuously fed into the air classification mill. The horizontally rotating grinding disc throws the product against the stationary grinding surface. Immediately after the impact, the process air escaping radially around the grinding disc carries the product out of the grinding area to an integrated air classifier. The air classifier speed prevents particles exceeding the primary grain size from leaving the mill. These particles are recycled into the grinding zone. Particles which are smaller than the primary grain size are led through the air classifier wheel by means of process gas and are separated in a subsequent filter. (Figure 4 + 5)

Recycling to the grinding zone is repeated until the entire product to be ground has been reduced to the desired primary grain size. Feeding and discharge are kept in balance by an automatic control system of the mill. Thus, overfilling of the mill is impossible. (Figure 6)

The product is transported out of the mill and is now available in the modified main components of the endosperm (starch and protein). Partly, protein particles with grain sizes of < 15µm attach to the starch particles. The starch granules are no longer enclosed in the matrix of the endosperm. They are undamaged and available as primary grains with grain sizes 25 to 35 µm. The different bulk density of protein and starch particles is a relevant factor for the following process step.

d. Hosokawa Alpine High-capacity air classifier:

In the high-capacity air classifier, an optimum dispersion of the ground product is achieved. Due to the design of the classifier wheel, a sharp separation is achieved, which ensures an optimum fractionation into fines and coarse product. Due to the division of the process gas into a central air flow and an air flow circulating along the inner wall, the coarse product is cleaned thoroughly before it leaves the air classifier casing. (Figure 7)

This ensures a clean coarse product and thus a maximum starch content. Due to protein shifting into the fines fraction, the starch content in the coarse product fraction increases proportionally. The diagram illustrates the interrelation between protein and starch in the fines and the coarse product. An increase of the starch content in the coarse fraction inevitably results in a reduction of the protein content in the fine fraction.

The usual yield of fine product is approx. 30 to 35%. As is represented in the diagram, this causes protein values in the fines fraction of approx. 53 to 55%. Under this condition, the coarse fraction has a starch content of approx. 67 to 73%. (Figure 8)

e. Amandus Kahl pelleting press:

For decades Amandus Kahl pelleting plants have been applied successfully for compacting organic products of different particle sizes, moisture contents, and bulk densities.

The product is pressed through a die by pan grinder rollers, formed into endless strands, and then cut to the desired particle length by means of knives.

With the Kahl pelleting press different products with regard to their structure, bulk density, binding strength, and particle size can be processed. Powdery, fibrous, lumpy, and pasty products can be processed into uniform pellets with different sizes. (Figure 9)

In the protein shifting process, Amandus Kahl pelleting plants are used for compaction and shaping of the three fractions of starch and protein concentrate and the seed coats. Only this process step makes storage and transport feasible.

Future prospects for feedstuff and food producers

The described process enlarges the range of vegetable proteins that can be used in the feedstuff and food industry. It offers new possibilities for the user in terms of provision, process engineering and distribution policy.

Thanks to the separation of the raw material into its main components fibre, protein and starch, custom-made products are obtained which meet the market requirements in many fields. More flexible and custom-made products increase the value added in processing from raw to finished product for the feedstuff and food industry.

There is a great number of advantages for feed producers:

  • Optimised concentrates of protein and starch
  • Use in monogastric animals is also possible thanks to the reduced fibre content
  • Wider range of resources and thus cost-saving provision
  • Substitution of animal proteins in the formula is possible due to amino acids from vegetable proteins
  • Low microbial risks
  • High margins can be achieved in the food industry
  • High nutritional value of protein concentrate due to the high lysine content
  • No genetic engineering, ecological cultivation
  • The seed coat is rich in hemicellulose which becomes increasingly important in nutrition physiology (civilisation diseases)

Applications in industry:

  • Starch concentrate is used in the starch production process. Only genetically modified starch-containing plants have a similar starch content of > 70 %!
  • Substitution of urea-resin glue (on the basis of urea and formaldehyde) in the cardboard and in the plywood production
  • Use for biodegradable plastics for foils and packing material
  • Raw material for alcohol production - due to higher quality of the raw material a higher quality of final products is obtained