Table 2.2 Comparison of added water levels with different doughmaking processes (same flour).
Water addition
Process (% flour weight)
1-h bulk fermentation time 57 4-h bulk fermentation time 55
No-time, spiral mixer 58
CBP – atmospheric pressure 60
CBP with partial vacuum 62
CBP with pressure 58
Typical levels of water addition to the same flour processed by different breadmaking processes are given in Table 2.2.
In those breadmaking processes that require a significant input of en-ergy to the dough during mixing, e.g. the CBP, optimisation of water levels plays a part in the energy transfer mechanism. In particular, the rate of energy transfer is affected by the consistency of the dough. Soft doughs offer less resistance to the action of the mixing tool, and energy transfer rates are therefore lower. However, within the range of dough consistencies that would give doughs suitable for handling and process-ing, the differences in energy transfer rates are small and therefore have only a small effect on mixing times. If doughs are mixed to a specified energy input, as in the CBP (Cauvain and Young, 2006), the impact of changes in dough consistency on dough development is minimal, but when doughs are mixed solely to time, then the impact may be appre-ciable. In the latter case, softer doughs may receive lower energy inputs, yielding doughs with less development and poorer gas retention and ultimately bread with less oven spring and smaller volume and firmer crumb.
It is inevitable that some (mainly small) variations occur in the wa-ter absorption capacity of flours, and it is these changes that millers and bakers seek to measure and predict. While the water absorption capacity of a flour may be the subject of a ‘fixed’ specification agreed between the miller and baker, it is worth noting that the ‘correct’ water absorption is the one that provides the baker with a standard dough consistency that can be processed readily, and that the water absorption capacity of flour is therefore not an expression of a fundamental property of wheat flours.
Also, because of the viscoelastic nature of gluten structures (see below), we cannot simply take a measure of dough viscosity as an indicator of dough consistency or performance in any given breadmaking process.
These comments go some way to explain why different methods of de-termining the water absorption capacity of flours have been developed and continue to exist side by side in cereal testing.
For a given wheat, the flour water absorption capacity derived from it depends on the following properties:
r
Moisture content – the drier the flour, the higher the water absorption capacity.r
Protein content – the higher the protein content, the higher the water absorption capacity.r
Damaged starch – the higher the damaged starch level, the higher the water absorption capacity.r
Bran content – the higher the bran content, the higher the water ab-sorption capacity (wholemeal flour has a greater water abab-sorption capacity than white flour).r
Pentosan level – the higher the pentosan level, the higher the water absorption capacity.r
Enzymic activity – the greater the enzymic activity, the lower the water absorption capacity. This effect is seen most commonly in breadmak-ing processes with significant bulk fermentation (floortime) periods, and only when levels of enzymic activity are high with no-time bread-making processes.Largely because of the empirical nature of the assessment of the wa-ter absorption capacity of a given flour, there have been attempts to develop mathematical models to predict water absorption from flour properties such as those described above. The most common models (Farrand, 1969; Dodds, 1971) have linked flour moisture, protein con-tent and damaged starch. Cauvain et al. (1985) found similar correlation with those of earlier workers, and while they did not find that the best predictive equations included any measure of enzymic activity, they did find that their model over-predicted the water absorption for flours with low ‘falling numbers’ (i.e. high cereal alpha-amylase levels). Given the
very high water-absorbing capacity of flour pentosans, we could expect a term for this flour property to occur in correlations, but the relatively small variations in levels seen in pentosan quantity for different flours probably have too small an overall effect and are masked by the vari-ability inherent in the measurement of flour water absorption. A similar reasoning applies to variations in bran content within a given type of flour (e.g. white) and the effects become evident only when there is a major change in flour type, e.g. from white to wholemeal, or when sig-nificant quantities of bran (more than 2%) are blended into a white flour base (Cauvain, 1987). Zhang and Moore (1997) also found that additions of bran increased dough water absorption but that the particle size of the bran had no effect.
Given the difficulties associated with predicting the water absorption capacity of a flour from its other chemical and physical properties, it has become common to make a direct measurement based on an assessment of its performance in some form of a dough mixing test. The basis of such tests is to mix a dough and measure aspects of its rheology, either during mixing or afterwards. The ‘correct’ water absorption is identified when the dough meets a predefined rheological condition (e.g. resistance to deformation or viscosity), which has been set by calibration with an expert assessor who has judged the ‘correct’ dough consistency based on a sensory evaluation and experience in dough processing.
The most common method for determining flour water absorption is based on the use of the Brabender Farinograph (www.brabender.com).
With the Farinograph, the water absorption capacity is assessed by mix-ing a flour–water dough with known ratios of flour to water, and record-ing the resistance of the dough to the movement of the mixrecord-ing blades (e.g. CCFRA, 1991). Initially there is little resistance from the mixture, but as the proteins hydrate and form gluten the resistance increases (see Catterall and Cauvain, 2007). The results are recorded graphically and the operator is required to add sufficient water to reach a predetermined height on the graph. It may take the operator two or three attempts with freshly mixed doughs each time to determine the necessary level of water addition to meet exactly the required height on the graph.
There are several instruments suitable for the assessment of flour wa-ter absorption capacity which are based on the mixing of a dough to a standard or fixed consistency. They include the Rheologica Instruments Mixograph (www.rheologica.se) and the Newport Scientific Doughlab (www.newport.com.au; Bason et al., 2005). Near-infrared (NIR) tech-nology (Lindegren and Allvin, 2005) is now commonly used to measure the water absorption capacity of flours. This testing method is carried out on the dry flour and thus the mixing of a dough is avoided. How-ever, it should be noted that the values obtained by this method are based on correlations with methods requiring the production of a dough
(e.g. as with the Farinograph) and this may increase the size of the differences between the ‘predicted’ water absorption and the actual water level used in the bakery.
The value determined for the flour water absorption capacity should be taken only as a guide to the actual level of water to be added to the dough for mixing. Differences between the determined water absorption and the level of water used arise because it is common to determine water absorption based on a flour–water mix, while in baking other ingredients are present which will influence dough viscosity and its other rheological properties. The effects of some of these are discussed in subsequent sections in this chapter.
In the UK it has become the accepted practice to mix to a maximum viscosity on the 600 line of the Farinograph trace, but elsewhere the 500 line is still commonly used. Such differences arise from the use of different breadmaking processes and dough handling methods. If the same flour was used to make no-time and bulk-fermented doughs, the optimum water level to achieve the same dough consistency at the divider would have to be reduced with bulk fermentation in order to compensate for the enzymic softening that would normally occur during the prolonged fermentation period.