Effects of seasonal and short-term changes during storage on the breadmaking performance of home-grown wheat

Abstract

Breadmaking wheat varieties, representing different protein quality classes, were milled as soon as possible after harvest before being stored at -18oC (control flour) or under controlled conditions of 15-20oC and 50% relative humidity (stored flour). The remaining wheat was held under an equivalent storage regime to the stored flour and at pre-determined time-points samples were removed for comparison of milling and breadmaking quality potential. This protocol was devised to permit separation of the effects of wheat storage after harvest and normal flour storage over the same period (c.8 months) on end-use quality.

Post-harvest changes in wheat quality have been documented since the beginning of the century, but seasonal differences in fundamental quality due to growing or harvesting conditions may also be responsible for observed variability in processing performance of home-grown wheat at crop changeover. The magnitude and biochemical basis of this variability required investigation to provide end-users, millers and bakers, with the necessary information to optimise product consistency.

Optimum milling performance in a laboratory Bühler mill was generally not achieved until wheat had been subjected to a period of storage prior to milling. In particular, the endosperm appeared to be easier to separate from the bran and a slight increase in flour particle size was observed after storage. Sieving problems have been perceived by millers when using new crop wheat and increased granularity would be expected to improve flour flow characteristics. Unfortunately, the Instron method used to test ease of flour movement and potential for bridging proved too imprecise to enable a firm conclusion to be made on this point. Effects on milling performance were generally overcome by storage for approximately six weeks, confirming the value of blending old and new crop wheat at harvest changeover.

Storage, as wheat or flour, had no significant effect on basic chemical and rheological properties of white flour. Any observed changes in flour quality characteristics could be related to milling differences, i.e. increases in flour extraction.

Wheat storage prior to milling had no consistent, significant effect on final quality in a standard Chorleywood Breadmaking Process (CBP). Prolonged flour storage (of up to eight months) generally resulted in a deterioration in quality as indicated by reduced CBP loaf volume. This decline in quality was associated with increased free fatty acid levels and reduced sulphydryl content of flour.

There was no evidence of varietal susceptibility to post-harvest changes, but seasonal variations had a major impact on quality for breadmaking. The magnitude of season-to-season differences generally exceeded any wheat storage effect and no solution to this natural, annual variation in protein content and protein quality could be recommended from biochemical studies.