Deep drying flour / starch

By deep drying flour or starch we mean drying further than what is required to obtain a product with a stable shelf life. By removing more water and making a very dry product, the cell structure changes and with that the product’s functionality. this opens a new range of possibilities and applications.

Deep dried flour

The process to deep dry requires accurately applied heat input to evacuate the captured water from the cell structure but to not overheat the product. As a result, due to the changed cell structure, the process is irreversible. The final product dissolves easier in cold water. Applications are for example instant soups and sauces.

Similar to flour drying can starch be deep dried too. Both processes are quite similar. The heat treatment of flour does not involve any prior chemical or enzymatic modification. Modification prior to deep drying is common for starch.

Apart from that, deep drying of chemically modified starch is the first thermal step in the dextrinisation process. Read further about the dextrinisation process on our web page Dextrin.



Most flours and starches are called semi-perishable products. Yet
they still require drying to preserve them. By drying the products,
the amount of ‘free’ water present in the cell is reduced to a point
which will inhibit the growth of the organisms such as bacteria,
yeasts, and moulds. In the case of starches and flours, that point
is around 11-13% of final moisture in the product. Few products
like potato starch permit a higher residual moisture to become
stable for storage.

A small portion of the total water content in the product does not act as ‘free water’. Those water fractions are strong interactions such as the hydroxyl groups of polysaccharides, and the carbonyl and amino groups of proteins. And there are also the hydrogen bonding and by ion-dipole bonds that hold water tightly. All these binding actions are referred to as the sorption behaviour of the food.



To dry a product such as flour or starch, its excess of free moisture needs evacuation. For this the water needs to migrate from the product to the carrier, which is normally hot air. As the ‘free’ water is not bound, it easily migrates to the hot air. It results in a relatively high evaporation rate. The energy required for the evaporation ‘cools’ the product.

The more constant the evaporation rate is, the better the product is kept at a constant temperature (cooled) during evaporation. This protects the product from peak temperatures. Peak product temperatures result in uneven product functionality changes. On top of that, Maillard reactions occur between amino acids and reducing sugars causing the product to become browner.

Deep dried flour from the drying process

Flour from the milling process

Once the water is removed from the product beyond the point that there is no more free, non-bound water, the migration of water to the drying air stops. This causes the evaporation rate to drop considerably. As the evaporation ends, so does the cooling effect on the product caused by a lack of evaporation. As a result, the starch or flour heats up by the hot air. Heating up of the flour or starch breaks up some or all molecular groups and bonds. The captured water is now released and can be transferred to the hot air. This process is non-reversible: The product has changed.

Even though this drying process may have gone beyond the gelanitisation temperature of the starch granules, the absence of water around the cells prevented swelling as you have with pre-gel starches. It means that deep drying of flours and starches is fundamentally different to making a pre-gelatinised starch.

Click here to go directly to the pre-gelatinised starch section of the web page Starch.



Factory for deep drying of flour

Factory for deep drying of flour


On the one hand requires deep drying higher temperatures to break open the bonds in the cells that capture the water. On the other hand the product temperature should be as low and homogeneous as possible to not create partially burned product and too much Maillard reaction, creating a brownish product.

Short, effective and hygienic heat treatment is very important for deep drying of flour and starch. Separately, deep dried starch with moisture levels down to the low single digits, requires substantially less ignition energy to explode. Safety is crucial for this process!


For deep drying processes, Ingetecsa uses the static Spiral Flash Dryer for the following reasons:

  Unlike any other technology, the evaporation has proven to be very constant across the entire drying chamber. It cools the product more while evaporating. This makes a superior end product.

Principle of operation of the Spiral Flash Dryer

The constant evaporation in the drying chamber cools the product as much as possible

  The Spiral Flash Technology is static technology. It makes the drying chamber most hygienic and feedback from our clients shows that virtually no cleaning is required

  The Spiral Flash Technology has no moving parts in the drying chamber. Any risk of ignition energy by metal contact is impossible. It is extremely safe.

The Spiral Flash Dryer is probably the safest and best technology there is for deep drying of flour and starch.




The originally strong water bonds in the product have been broken under presence of heat. These bonds released their water fraction. These have been removed from the product during the deep drying process. As the bonds are broken. the deep dried flours have now the capability to easier absorb cold water. Often, deep drying of flours occurs to a residual moisture content of 5-8%.

Spiral Flash Dryer, a compact, safe and hygienic technology

The static Spiral Flash Dryer for superior and safest deep drying

Deep dried flour finds its way in instant products such as soups or sauces.


Deep drying of the starch thermally modifies it as it is an irreversible process. Depending on the final moisture content, properties change. Starch can be deep dried to as low 1%, although 3-5% is a more commonly range and around 8% also.

Starch is also deep dried in the dextrinisation process, prior to roasting.

Additional information on the dextrinisation process can be found on our web page Dextrin.



Deep dried flour used to make a sauce

Deep dried flour used to make a sauce


Have a look at our Spiral Flash Dryer or the brochure at the download section for more information about this technology.

If you are interested how we can help you with setting up a deep drying process, just get in touch with us.

We look forward to helping you. We have experience with deep drying different products such as wheat, corn, potato, tapioca, etc. and we can conduct tests in our test centre to simulate or optimise your process.

How can we help with deep drying

How can we help you with your deep drying question?