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Understanding the Role of Heat Treatment of Flour

May 4, 2017 – by Dr Mahmoud Riad, Egyptian Milling Society Secretary General, Egypt

Flour Heat Treatment (FHT) is a process designed to modify the properties of flour, germ and bran. FHT can be divided into two basic processes: hydrothermal treatment and thermal treatment.

Applications for FHT products can be applied in a large number of different ways in the food industry. This is because coatings where hydrothermally treated flour is excellently suited for preparing batters for coating fish, meat and vegetables.

Thanks to its optimised cold viscosity batters or breadings adhere perfectly to the food and dripping of the batter is reduced.

In bakery products thermally treated flours are used for cakes with high sugar and fat contents. These flours are characterised by their strengthened gluten properties and fine granulation.

In order to achieve a long shelf life of fresh dough, raw materials with low microbiological contamination are required. Heat treatment sanitises the flour by inactivating a large proportion of the microorganisms.


FHT flour is applied, among other things, as a thickener for soups and sauces.

Heat treatment increases the hot viscosity of these flours, dries the product to prevent moisture from migrating to the other substance components while inactivating microorganisms and enzymes.

Other applications

The FHT process allows bran, germ – that is from wheat – as well as rice bran to be stabilised, enabling them to be preserved by essentially inactivating fat-splitting enzymes, reducing a large proportion of the microorganisms by heat and optimising the product moisture.

These grain by-products can, for example, be used in muesli mixes or in cereal bars.

Hydrothermal flour treatment involving moisture and heat is a hydrothermal process. The term ‘hydrothermal process’ refers to the treatment of flour by heat and moisture in the form of water and steam.

The goal of this process is to modify the flour substance components such as starch and gluten.

In addition, enzymes and microorganisms are inactivated.

The principle

FHT is a continuous process with a throughput capacity up to 2500kg/hour.

Hydrothermal flour treatment can be divided into three steps:

  1. Injection of steam and water into the flour, followed by a retention time in the heat retention screws
  2. Gentle drying by hot air in thermopneumatic conveyors
  3. Removal of agglomerated particles by sieving, which are then ground

The goal of hydrothermal treatment is to increase the hot and cold viscosity by gelatinizing the starch while improving the water solubility by denaturing the gluten and inactivate enzymes in grain byproducts such as germ and bran to improve the shelf life.

The ‘thermal process’ of flour treatment involves heat and retention time.

The term ‘thermal process’ refers to the treatment of flour by heat, followed by an appropriate retention time. This process is less intensive than the hydrothermal process. The flours thus retain their baking characteristics. The heat acts particularly upon the gluten and the microorganisms.

The principle involved in the ‘thermal process’, which allows a throughput capacity up to 2000kg/hour of product. The process can be divided into the following discrete steps:

  1. Gentle heating in a current of hot air in thermopneumatic conveyors
  2. Temperature retention in heat retention screws
  3. Moisture addition to adjust the water content
  4. Screening and grinding to adjust the particle size

Unlike hydrothermally treated flours, thermally treated flours retain their baking characteristics. Such flours are applied as cake flour with strengthened gluten framework, for cakes with very high sugar and fat contents, plus soup flours with increased hot viscosity and low moisture content.

Overall process

System types:

The core components of all FHT systems (heat retention screws and thermopneumatic conveyors) for the ‘hydrothermal’ and ‘thermal processes’ are identical.

The two processes can be combined in one single system. This produces maximum production flexibility, since it is possible to produce flours with gelatinised starch, baking flours with strengthened gluten, dried flours and stabilised germ and bran.

A single system may also be designed to meet specific process requirements. The system capacities are related to the specific product and may vary according to the process used – thermal/hydrothermal – the heat retention time in the retention screws and the intensity of treatment.

The process and the system size are matched to the customer’s specific needs.

Sourced by Milling and Grain

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