Latest PGRO Pulse Crop Bulletin: Drying and storage tips for peas and beans.
Becky Ward, PGRO senior technical officer, advises:
Peas
The quality standard for peas ex-farm is usually 14% moisture content (MC) and 2% impurities – or a combination of both, which should not exceed 16%. Whilst damaged peas are still acceptable for compounding, mouldy produce is not. Care must be taken not to over-dry peas for human consumption or seed.
Drying temperature should not exceed 49C for human consumption, and 43C for seed if the MC is below 24%. If the MC is higher, 37C should be considered the maximum for seed and 43C for human consumption.
Any type of drier may be used for peas, but those operating at low temperatures are safer:
* Floor-ventilated bins are easy and relatively safe to operate.* Radially ventilated bins allow faster drying than floor-ventilated bins, but care must be taken not to overheat the peas.* On-floor drying using ambient or warmed air can be used and, provided there is sufficient volume of air and adequate ventilation, peas of relatively high MC can be dried using this method.* Continuous flow driers designed to work on a short period/high temperature basis need more careful operation than other systems.
Peas may be stored up to 4 weeks at 17% MC, but if they are to be stored until the following spring the MC should not be above 15%. If the peas are in bulk with forced ventilation or frequently moved the moisture content can be 1% higher.
Beans
The quality standard for beans is the same as for peas, but merchants may accept beans at 16% MC. Beans must be dried down to 14% for long term storage in bulk. This is important as beans are often stored for some time before they are sold.
The large size of beans makes drying difficult as beans have a low resistance to air flow. It takes time to move moisture from the inside to the outside – hence slow, gentle drying with ambient air is best. Mouldy produce is unacceptable for animal feed or other markets.
As with peas, any type of drier may be used, but those operating at low temperatures are safer:
* Floor ventilated bins are suitable. When the initial MC is high, transfer of beans from bin to bin and use of warmed air together with adequate ventilation may be necessary to avoid mould developing in the upper layers.
* Radial ventilated bins allow faster drying than floor ventilated bins but, as with peas, care must be taken not to overheat the produce.
* On-floor drying using ambient or warmed air is also successful but care must be taken not to load beans too deep if MC is high and lateral ducts are spaced wider than 1m.
* Where high quality is important, high temperatures in continuous flow driers should be avoided as they may cause cracking.
To delay the development of tannins which cause beans to discolour, storage in dark areas is recommended for beans destined for the human consumption market.PGRO is the non statutory levy body which promotes and carries out research and development in peas and beans. PGRO growing guides and recommended lists of varieties are the national references for growers. The PGRO publishes ‘The Pulse Magazine’ quarterly, the ‘Pulse Agronomy Guide’ annually, issues bulletins during the growing season, provides education and training courses, and runs grower / agronomist meetings around the UK.