RHEOLOGY AND THE CONTINUOUS BREADMAKING PROCESS

Modern continuous breadmaking processes h a v e e v o l v e d f r o m a c o m m o n aim-elimination of the lengthy conventional bulk fermentation needed to mature dough proteins. The various ways in which this has been ach ieved , based o n m e c h a n i c a l development of the dough, are briefly traced and the rheological behavior of dough under intensive mixing conditions is discussed. with particular regard to 'optimum development. ' Aspects considered include mixer speed and geometry, rates of mechanical work input and total work levels applied to the dough. Rhcological methods for the control of mechan ica l d e v e l o p m e n t a n d d o u g h consistency are also reviewed, and a new computing dough mixer for research in to mechanical development is described. Finally, the different indications of 'optimum' development obtained f rom recording mixers and f rom the tcsting of rested doughb are discussed, and it is concluded that dough development is dependent on a complex relation between mechanical work and the action of chemical oxidiring and reducing agents. The elimination of bulk fermentation from bread manufacturing processes by the use of mechanical means to mature the dough is not new. As early as 1926 Swanson and Working ( I ) described a 'no-time' dough method based on a pin mixer running at moderate speed (60 or 120 rpm) the action of which was sufficient to satisfactorily modify the gluten proteins without bulk fermentation. Although provision was included for power measurement, no attempt was apparently made to quantify dough development in terms of work input and with some flours overmixing occurred (2). The lack of guidance in respect of the degree of mechanical modification required and its control in mixers of different design, together with problems in handling the resulting doughs (3), probably explains why commercial adoption of mechanical dough development was so slow to follow. Not until the experiments of J. C. Baker, 25 years later, culminating in the 'Domaker' continuous breadmaking process ( 4 3 , were the practical problems of high-speed developer design solved and accepted by the breadmaking industry. Neither the 'Do-maker' process nor the continuous sponge-and-dough 'Amflow' system (6,7), which followed 5 years later, made provision for automaticcontrol of work input during dough development, although it was implied in the original 'Amflow' patent (8) that an energy input of 40 kJ kg-' (0.4 HPmin/lb; 5 Whr/lb) should be used. Further investigations into the factors involved in the production of bread from mechanically developed doughs were undertaken a t the Flour Milling and Baking Research Association, Chorleywood, England. It was found that, irrespective of formulation, the best bread was produced when work expended on the dough fell between 37 and 46 kJ kg-' (9). The outcome of this was the definition of a batch mechanical development process known as the 'Chorleywood Bread Process' (10-14) in which a mixer of sufficient power was employed to expend 40 kJ of energy per kg dough over a period of time preferably not exceeding 5 min (i .e., an average rate of work input of 8 to 10 kJ kg-'min-I).