Question and Flour Problems : Rheology & Falling Number

1.What is rheology?

Rheology is the branch of physics that deals with the elastic and plastic properties of systems and their flow characteristics. When combined with water, flour forms more or less viscous systems that solidify when baked. The science of rheology can provide information on quality in both states-baked and unbaked.

2. What are “basic rheological properties”?

Basic rheological properties are the parameters strength, viscosity, elasticity and plasticity. They are determined by measuring the effects of deformation forces on the dough. These forces may be of any magnitude, and the measurements are correspondingly large or small. For the rheology of dough the most important properties are viscosity and elasticity.

3. What am I to make of the “flowery” descriptions of the properties of dough and baked goods that are so popular with bakers?

The observations of experienced bakers and the resulting jargon are still very valuable for describing product attributes that may also be problematic. Examples : silky; shred.

Falling Number

1.Why is the stirring time included when the Falling Number is determined?

This was probably for historical and also practical reasons. The glass tube for determining the Falling Number was inserted into the boiling water bath and a manual stop watch was immediately started to monitor and control the stirring time. It would have been impractical – an extra step – to stop and re-strart the watch manually at 60 S. Note that there was, and still is, an initial pause of 5 S and then actual stirring for 55 S to make a total of 60 S before  the stirrer released from the top position. Presumably the operator started the watch, rapidly put down the tube with the stirrer in the bath, and then had 5 S to turn a lever over the tube so it became fixed in the bath, and thereafter started the stirring at 5 S.

2. What conclusions can be drawn from the Falling Number?

The Falling Number determines the viscosity of a flour-and-water suspension heated to just below boiling point by measuring the time a pestle takes to sink through the gelatinized starch. Low Falling Numbers indicate a degraded gel. The higher the Falling Number, the better ate the remaining viscosity and the processing characteristics. A low Falling Number is accompanied by a high level of amylases naturally present in the grain; it is therefore an indication of sprouting.

3. What influence do fungal amylases have on the Falling Number?

In the concentrations at which they are normally used in flour treatment, added fungal amylases have scarcely any effect on the Falling Number since they are heat-labile and inactivated by heating. Fungal amylase can be determined with a modified version of the Falling Number measuring device (in which the final temperature can be set).

4. What baking properties do flours with low or high Falling Numbers have?

Doughs made from flours with low Falling Numbers tend to have moist surfaces and low stability, but browning, flavour formation and the shelf-life of the crumb (softness) are good. If the enzyme activity is too low the products “bake dry”, i.e. the crumb is not succulent enough and its shelf-life is reduced.

5. How can I reduce the Falling Number?

Only enzymes with a certain heat-stability, e.g. cereal or bacterial amylases, have an effect in the conventional Falling Number method. Since most bacterial amylases would survive the baking process and therefore liquefy the crumb of the bread, cereal amylases in the form of malt flour or malt flour extracts have to be used. Although fungal amylases cannot be detected in the Falling Number tests they nevertheless enhance the baked products.

6. How can I increase the Falling Number?

By reducing the yield in order to remove those layers of the wheat kernel that have a higher amylase content, or by using a buffer to shift the pH into a range that is no longer optimal for the enzyme. Although a higher Falling Number my seem desirable to achieve certain specified flour properties, it is important to keep the bakeability of the flour and the attributes of the end product in mind.

7. Can I risk buying wheat with a Falling Number below 200 S?

Yes, if you can mix it with wheat with a higher Falling Number. You can estimate the Falling Number of a mixture by the following method :

a.Use the following formula to calculate the Falling Number Index (FNI) of the two flours to be blended (FNI_A and FNI_B) and the desired Falling Number (FNI_T) of the blend :

b. Calculate the ratio of the two flours in the blend with the aid of the FNI, e.g. using the rule of three (“blending cross”) or the following formulas :

P_A = [FNI_B – FNI_T]

P_B = [FNI_A – FNI_T]

PA and PB are the proportions (absolute values) of flours A and B in the blend, expressed in parts. Together, the parts make up 100%. The proportion of flour A in the blend, expressed in percent, would therefore be :

And that of flour B :

The blend thus calculated should be tested with the Falling Number device before being run at the mill.

8. Can I risk buying wheat with a Falling Number above 400 S?

Yes, in fact many wheat lots from Australia and North America do have an FN in this range. The reduced fermentation capability can easily be increased with enzyme preparations. But beware of lots from regions that do not normally supply wheat with a high Falling Number : the high FN may be a sign of heat damage.

9. Is it safe to buy wheat with an FN above 600 S?

Although they are fairly rare, Falling Numbers above 600 S can occur in sound wheat, especially in lots from Australia. Nevertheless,  attention should be given to the gluten properties : a very short or – worse still – a crumbly gluten would mean heat damage.

10. Does xylanase affect the FN ?

Yes, because the hydrolysis of pentosans also reduces the viscosity of the flour slurry. But the effect is far smaller  than that of amylase.