Effect of temperature management methods on firmness uniformity of commercially ripened cannery pears

The effect of natural convection or forced-air temperature transition durin g commercial storage and ripening of 'Bartlett' pears (Pyrus communis L.) i nfield bins on fruit firmness uniformity following ripening was investigate d. Time required for natural convection or forced-air cooling of fruit to 0 degreesC and re-warm to 20 degreesC was profiled in standard wooden bins a nd in higher ventilated plastic bins. Firmness of fruit sampled throughout the bins was analyzed with respect to their position in the bins during sto rage and ripening. Pears experiencing natural convective cooling or warming in standard wooden field bins obtained seven-eighths temperature transitio n across the whole bin within 18 and 34 h of each other respectively. In pl astic field bins, seven-eighths temperature transition occurred within 11 a nd 10 h of each other respectively. Under a forced-air velocity of 0.41 m s (-1), pears in wooden or plastic field bins obtained seven-eighths temperat ure transition across the entire bin within 3.6 and 4.4 h of each other res pectively, for both cooling and warming. Firmness uniformity of sized, comm ercially ripened pears was not improved by forced-air cooling as opposed to natural convective cooling during the initiation of cold storage; however, forced-air as opposed to natural convective cooling of unsized pears impro ved firmness uniformity, possibly due to more consistent cooling times betw een adjacent large and small fruits. The variability in firmness of the rip ened, sized, and unsized pears in the bins increased due to firmer fruit in the bottom of both wooden and plastic bins, irrespective of their exposure to forced-air or natural convective cooling during cold storage initiation or warming at the initiation of fruit ripening. This increased firmness va riability was largely attributed to fruit temperature transitions resulting from unstable air temperatures during commercial ripening. Results indicat e the benefit of improved firmness uniformity in fruit sorted for size prio r to cold storage, and ripened under stable ripening room temperatures.