Effect of Frost on Wheat at Progressive Stages of Maturity: Iii. Milling and Baking Quality

Abstract

The yield of flour from unfrozen samples of wheat cut at progressive stages of maturity increased until the dry matter of the grain at the time of cutting reached 58%, and thereafter remained constant. Frost exposure reduced the flour yield at all stages of maturity, the reduction being roughly proportional to the immaturity of the sample and the severity of the exposure. The yield from mature, frozen samples was slightly but definitely lower than that from comparable unfrozen checks.The baking quality of the unfrozen checks was relatively high, even when the wheat was cut while immature. Frost exposure reduced the quality of immature samples in proportion to the immaturity of the grain and the severity of the exposure, but had little if any effect on mature samples. Flour from immature, frozen samples deteriorated in storage more rapidly than did that from the unfrozen checks.Reduction in flour yield was proportional to reduction in grade but reduction in baking quality was, on the average, less than anticipated from the grading results.The earlier conclusion is confirmed that 58% dry matter represents a critical stage in the development of wheat, and that all samples harvested after this stage can be considered mature.

Effects of frost during grain filling on wheat yield and grain structure

“…Heavily frosted samples may be harder to mill than unfrosted samples owing to the tough and fibrous nature of the "middlings" (Newton & McCalla 1935). These mostly comprise the aleurone layer and possibly nucellar layer and seed coat, probably corresponding to the disorganised nature of the aleurone we observed under the SEM.…”

“…Blisters were observed in samples from the Southland crops in the present study, although blisters were masked by the extensive shrivelling of grains. Presence of blisters on the surfaces of grains can increase the bushel weight (Newton & McCalla 1935), but the reduction in grain volume experienced in Southland grains suggests that frost occurred at an earlier growth stage than usually occurs in Canada, with total effects being more severe.…”

“…The presence of blisters on the surfaces of wheat grains is considered diagnostic of frost damage in Canada (Newton & McCalla 1935); those where blistering is carried down into the crease are categorised as having experienced "heavy frost" whereas other blistered grains are categorised as "bran frosted". Blisters were observed in samples from the Southland crops in the present study, although blisters were masked by the extensive shrivelling of grains.…”

“…Marcellos & Single (1984) demonstrated disruption of membranes of recently emerged ears of wheat at temperatures below -4°C. Grains affected by frost during grain filling may be small, shrivelled, shrunken, or merely have a blistered appearance on the back of the grain (Newton & McCalla 1935). However, in every crop there are missing or shrivelled grains caused by factors other than frost.…”

“…data). Published studies of frost damage to wheat have focused on frost within 2 weeks of full maturity (Newton & McCalla 1935;Dexter et al 1985). In our study, the effects of frost at early grain fill are characterised.…”