The development of an integrated storage strategy for malting barley

Abstract

Practical significance

This project establishes useful guidelines for storing malting barley, but automated control and aeration is essential. The job is best left to specialists.

Summary

This report describes experiments to determine the best storage strategy to break dormancy, preserve germination and discourage infestation in malting barley. The objectives of this project were to establish a model for time/temperature combinations required to break dormancy in the most difficult variety (Triumph) and calculate subsequent germination loss during cool storage. These predictions were combined with calculations and experiments on insect increase to determine the infestation potential of different strategies during the phases of dormancy break and subsequent cooling The effects of sudden cooling on germination were examined to check for 'secondary dormancy' and the dormancy of the most troublesome varieties was compared to check that the model was representative. Information on current storage practices were collected, to see if these were compatible with the proposed strategy. Finally, commercial-scale trials in the north and in the south of the country were carried out, in order to validate some of the storage strategies for malting barley.

Predictions based on laboratory work indicate that dormancy can be broken so that germinative energy rises from 10% to 95% in 24 days at 30°C and 12% moisture content (m.c.) or 12 days at 40ºC and 11% m.c. Higher final germinative energies are achievable at lower temperatures but longer storage times. For instance, it takes 50 days to break dormancy at 20°C or 80 days at 15°C.

Calculations based on speed of insect development and fecundity show that lower temperatures gave greater safety margins between insect development time and break of dormancy. Saw-toothed grain beetles were the quickest developing insects at high temperatures with little margin for error between dormancy break and development times. Most strategies allowed theoretical insect development after dormancy break and during cooling. Rust red grain beetles were the greatest threat at 35°C, saw toothed beetles at 25-30°C with few insects developing at 20°C where grain weevils predominated.

Laboratory experiments at 20, 30 and 40ºC simulating times for dormancy break, cooling and subsequent storage showed that at 40ºC, no insects tested were able to survive. At 30ºC, moderate insect numbers developed during dormancy break and cooling but they failed to survive in subsequent storage. At 20ºC, few saw-toothed beetles developed during dormancy break and cooling and none survived storage but large numbers of grain weevils developed and half of them survived storage.

A sudden drop in temperature did not induce secondary dormancy and the prediction model for germination changes at steady temperature was effective during a change of temperature.

The varieties Triumph, Blenheim and Pipkin were identified as barleys more prone to dormancy. Triumph emerged from dormancy more slowly than Blenheim or Pipkin. For a given change of temperature the rate of emergence from dormancy increased by the same factor for all three varieties.

A survey of maltings storage showed that most storage has aeration but virtually none has automated control. Most grain was stored for over ten months, showing the potential to minimise carry-over stocks. Most grain was initially stored at the optimum temperature for insect development.

Experiments in cooling 1,000 t bins in the south of England showed that initial cooling to 15-20ºC in tall silos was as fast as expected and as fast as in flat stores but subsequent cooling to 10ºC was unexpectedly difficult. Hot barley cooled by upward aeration late in the year required special measures to avoid roof condensation. Neither grain weevils nor saw-toothed beetles survived the storage strategy at initial temperatures of about 22ºC but at just under 40ºC, there was development of grain weevils after three to four months.

Similar experiments in the north of England showed that monitoring grain temperature off the drier was essential to control the initial warm storage temperature. Although storage temperatures were higher than the recommendations based on laboratory work, maltable barley was still produced. A 'dryeration' effect reduced moisture contents to 10-11% during cooling, further protecting the barley from loss of germinative capacity. Higher differential settings on the fan control reduced moisture pick-up. The high temperatures (above 40ºC) at the northern site killed all insects. Downward air flow avoided condensation in the roof space but the disadvantage of downward air flow was that regions of low airflow between the vents at the base of the site were the last to be cooled and were also more difficult to cool.

Storage of malting barley between 25ºC and 35ºC to break dormancy before cooling is a high risk strategy which encourages infestation. This risk can be minimised by using the information on dormancy break, germination loss, cooling rates and insect increase that is contained in this report. Ultimately the data could be made available in the form of a decision support system for maltsters. Automated fan control, purpose built for the malting industry should be developed alongside such a decision support system.