Aeration of Biscuit Doughs During Mixing

Biscuit manufacture can be viewed, like breadmaking, as a series of aeration stages, in which bubbles are incorporated into the dough during mixing, removed to some extent during sheeting, and the aerated structure modified and set during baking. Altering the aeration of biscuit doughs during mixing could potentially modify baked biscuit texture, provided that the mixing conditions change aeration significantly, and that these changes persist following sheeting. To investigate this, biscuit doughs were mixed under three different headspace compositions of varying levels of CO₂ and N₂, and at four different pressures, to investigate the effects on dough aeration and rheology, degassing during sheeting, and biscuit texture and physical characteristics. The void fraction of gas in doughs mixed under higher concentrations of CO₂ and at pressures greater than atmospheric pressure was significantly increased. By contrast, the gas content of the dough mixed under partial vacuum and 100% CO₂ was lower than that of the dough mixed under 100% N₂ and partial vacuum. Sheeting resulted in degassing of the doughs, the extent of which depended on the nature of the sheeting regime. Gentle sheeting (in which the final thickness was achieved after numerous small reductions) gave more degassing of the dough than Severe sheeting (in which the final thickness was achieved in a small number of large reductions). Increasing the gas content of doughs by mixing under higher positive pressure and a higher concentration of CO₂ resulted in a greater extent of degassing during sheeting. However, the more aerated doughs still retained significantly greater amounts of gas after sheeting compared to doughs mixed under atmospheric conditions. This indicated that initial differences in aeration were preserved sufficiently following sheeting that they could then potentially alter the biscuit texture. Biscuits obtained after mixing doughs under higher concentrations of CO₂ and/or higher pressures were significantly softer, and spread and lifted more during baking. Thus it has been demonstrated that mixing under varying headspace gas compositions and pressures affects biscuit characteristics and offers a route to produce biscuits with novel textures and enhanced consumer appeal.