Chapter 5 Temperature - Grain Storage Guide

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Chapter 5 Temperature - Grain Storage Guide Powered By Docstoc
					                                                                                                                         Grain will be relatively warm post-har vest – ideal for

5                           TEMPERA TURE                                                                                 insect breeding and activity. Grain is a good insulator
                                                                                                                         and loses heat very slowly.


BACKGROUND                                                                                                               ISSUE                                                 ACTION
Insect,mite,fungal and mycotoxin                                                                                         Temperature effects
development are controlled b y                                                                                           Cool storage extends grain storage life.It reduces    q Reduce grain temperature by low volume
temperature. At temperatures found in                                                                                    germination loss,maintains baking qualities and         aeration:
grain stores,biological activity of insects,                                                                             protects against infestation.                           – to below 15ºC within 2–3 weeks to prevent
mites,fungi and grain itself, doubles for
                                                                                                                         Cool storage permits grain to be stored at higher         saw-toothed grain beetles completing their life-
every 10ºC rise in temperature.
                                                                                                                         moisture contents.                                        cycle.
Insect breeding actually stops at lo w
                                                                                                                         Lowering the temperature lowers the relative            – to below 12ºC within 4 months to prevent
temperatures. Also,less moisture is
                                                                                                                         humidity in equilibrium with the mc.This                  grain weevils completing their life-cycle.
available for potential pests in cold g rain.
                                                                                                                         effectively increases storage time.                     – to below 5ºC by end-December to kill surviving
Therefore,as g rain comes into store it
should be cooled immediately to pr event                                                                                 – Hot air in a continuous dr yer is likely to             adult insects and to prevent mites increasing
insects breeding.                                                  Automated                                                 disinfest grain. As grain cools naturally it          (malting barley should not be cooled belo w
                                                                   temperature                                               becomes vulnerable to infestation.                    10ºC – a practice which may increase the risk
This will e ven out or equalise temperature g radients
                                                                   records                                               – Above 40ºC,most insects die within a day.               of infestation).
and so pr event moisture translocation.
                                                                                                                         – Most insects breed rapidly at 25–33ºC.Most            – when grain is moist,eg 15–18% mc,while it
                                                                                                                             insect species do not breed below 15ºC but            awaits drying due to har vest backlogs.
Temperatures fall more rapidly and to lower                                                                                  grain weevils can reproduce slowly at 12ºC.         EXCEPTION
levels when using automatic compared to                                                                                      Below 5ºC insects cannot feed and slowly die.         Dry high moisture content grain (at or above
manual fan control
                                                                                                                         – Mites and fungi can increase (although ver y            18% mc) immediately to prevent mycotoxin
                                                                                                                             slowly) down to 5ºC in moist grain.                   formation.
                                                                                                                         – Mycotoxin formation is most likely between          q Monitor temperature regularly (every few days
                                                                                                                             15ºC and 25ºC.                                      until target temperatures are reached,and then
                                                                                                                         Currently, targets can be achieved in given             weekly).
                                                                                                                         timescales.However, if autumns become warmer
                                                                                                                         this may become more dif ficult to achieve
                                                                                                                         consistently.


                                                                                                                         Causes of grain heating
                                                                Permanent probe arrays can be linked to record           When warm air from the centre of a bulk or bin        q Aerate grain immediately post-harvest to even
                                                                keeping software to identify potential problems.         meets cold grain at the surface,condensation may        out temperatures.
                                                                                                                         occur. Moisture at the surface or in damp pockets     q Check temperatures regularly across the bulk –
 Effect of different temperatures on insect and mite infestation risk                                                    in the bulk will encourage moulds,heating and           particularly areas furthest away from the duct in a
                                                                                                                         sprouting.                                              blown aeration system or closest in a suction
   Risk         ºC   Effects on insects                                Risk       ºC    Effects on mites                 Developing grain weevils may also generate heat.        system.
                60   Death in minutes                                             60    Death in minutes                                                                       q Cool intermittently, even when grain temperature
  Least              Death in hours                                    Least            Death in hours
                50                                                                50                                                                                             has fallen,to counteract ‘hot-spots’developing.
                     Development stops                                                  Death in days
                40   Development slows                                            40
                                                                                        No increase
  Greatest      30   Maximum development rate                                     30
                     Development slows                                 Greatest         Maximum development rate
                20                                                                20
                     Development stops but all stages survive                           Development slows
                10                                                                10
                     Insect death in months,movement stops
                 0                                                                 0    Lowest development rate
                     (fungi can still grow slowly in damp grain)
               -10   Death in weeks                                               -10   Death in weeks
  Least                                                                Least
               -20   Death in minutes,insects freeze                              -20   Death in minutes, mites freeze



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Description: Chapter 5 Temperature - Grain Storage Guide