Jim Scrimshaw, PGRO Principal TechnicalOfficer, advises on drying and storage of combining peas and field beans thisseason.
The quality standard forpeas, ex farm is usually 14% MC (moisture content) and 2% impurities – or acombination of the two should not exceed 16%.
The relatively largeseed size of peas makes drying more difficult than with cereals. Whilst damagedpeas are still acceptable for compounding, mouldy produce is not.
Considerable care must be taken not to over-dry peasas, at higher temperatures, a tougher texture or splitting of the grain mayresult. Whenthe moisture content is high, two dryings may be necessary. At least two daysshould be left between them to enable the moisture to spread evenly throughoutthe bulk.
The table below details the maximum recommended dryingtemperatures:
Max drying temperature
Floor-ventilated bins are easy and relatively safe to operate. When theinitial moisture content is high, the transfer of the peas from bin to bin andthe use of warmed air together with adequate ventilation may be necessary toavoid mould developing in the upper layers.
Radially-ventilated bins allow faster drying than floor-ventilated bins, butcare must be taken not to overheat the peas.
On-floor drying using ambient or warmed air can be used, and providedthere is sufficient volume of air and adequateventilation, peas of relatively high moisture content can be dried using thismethod.
Continuous flow driers designed to work on a short period/high temperaturebasis need more careful operation than other systems.
For safe storage, the maximum moisture content of peas depends upon themethod and the length of time they are to be stored. Peas may be safely storedfor up to 4 weeks at 17% MC, but if they are to be stored until the followingspring, the moisture content should not be above 15%. If the peas are in bulkwith forced ventilation or frequently moved, the moisture content can be 1%higher.
The quality standard,ex-farm is usually 14% MC and 2% impurities – or a combination of the twoshould not exceed 16%. Merchants may accept beans at 16% MC.
The large seed sizeof beans makes drying difficult as beans have a low resistance to air flow. Ittakes time to move moisture from the inside to the outside hence slow, gentledrying with ambient air is best. Mouldy produce is unacceptable for animal feedor other markets. The table below details the maximum recommended dryingtemperatures:
Maximum drying temperatures – Beans
Max drying temperature
34 – 38C
38 – 43C
43 – 49C
Floor-ventilated bins are suitable. When the initial moisture contentis high, transfer of beans from bin to bin and the use of warmed air togetherwith adequate ventilation may be necessary to avoid mould developing in theupper layers.
Radial-ventilated bins allow faster drying than floor ventilated bins, butcare must be taken not to overheat the beans.
On-floor drying using ambient or warmed air is also successful, butcare must be taken not to load beans too deep if moisture content is high andif lateral ducts are spaced wider than 1 m.
Continuous flow driers operated at high temperatures should be avoided wherequality is important since they may cause cracking.
Storagein dark areas is recommended for beans destined for the human consumptionmarket to delay the development of tannins which cause beans todiscolour. Beans must be dried down to 14%MC for long-term storage in bulk – this is important since beans are oftenstored for some time before they are sold.