HEAT STORAGE OF ONIONS

New Zealand Journal of Agriculture, Volume 66, Issue 1, 15 January 1943, Page 27

HEAT STORAGE OF ONIONS

REPORT ON TRIAL

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A. A. POWELL,

Cool Storage Officer,

Wellington.

The approximate average annual loss of onions during harvesting and storage is estimated to be 1000 tons. The losses which were borne by the grower, retailer and consumer during the past season would probably be more than double this quantity. In an endeavour to assist in establishing improvements in the drying or curing of onions in bulk, directly following their harvesting, the Department of Agriculture is investigating a system of grading onions for long storage and heat curing, and thereby minimising losses and maintaining a continuity of market supplies during the season.

THE economic value of the Dominion’s onion production will be more fully appreciated when it is realised that 1100 acres are planted with onions yearly, and the average estimated production is about nine tons per acre, a total of about 10,000 tons. The main areas of production are North Auckland, 500 acres producing 4800 tons; Canterbury, 400 acres pro-

ducing 4000 tons; these two areas yielding 8800 tons. The average price obtained for onions in normal times is in the vicinity of. £lO per ton; but under the present emergency conditions where importation of onions is restricted, realisations have increased considerably. Except in the north, the 1942 season was generally unfavourable to the production of onions of good keeping quality, and rots developed during and following harvesting. This condition resulted in the crop being marketed comparatively early in the season. Many growers experienced exceptionally heavy losses during storage, and the markets were practically without supplies for . the last three . months of the season.

It is estimated that one-third of the production of the main producing areas is required to supply the markets during the last three months of the year. With a view to assisting producers to develop an improvement in storage conditions which should extend

the storage period and enable them to supply the full market requirements throughout the year, the Department of Agriculture, with the co-operation of Messrs. A. D. and D. G. McFadden, onion growers, of Marshlands, is conducting a commercial experiment with the use of heat, and air circulation, for the curing and storage of onions. Results of Trial The results of this season’s trial have proved—1. The selection of onions for longperiod storage is of vital importance to

their successful keeping, and to the conservation , and regulating the marketing of supplies. The best keeping variety grown in New Zealand is the Pukekohe Longkeeper raised by John Turbott; but only sound lines of this variety should be selected for long storage purposes. The other varieties, and grades should be placed in the market according to their condition and keeping quality. 2. Heat storage, and the use of an electric heating and air circulating system installed in an insulated chamber

have proved to be practical,, and economical for thoroughly, drying the skins, and stem-end, tissues- of onions. Under these conditions drying or curing is brought about by the relationship, between temperature and relative humidity, and the wide optimum temperature range, as compared with the narrow optimum humidity range. 3. To assist the drying or curing, and storage of onions,; a properly designed system of air distribution is essential, together with facilities which will provide for the ventilation of the storage chamber. The Storage Chamber The storage chamber, having 3024 cubic feet of storage space, and a capacity of 24 tons of onions was erected in one end of Mr. A. D. McFadden’s ordinary onion storage shed, and was ready for storage on July 3. An illustrated description of the experimental chamber and a statement setting out the objects of the trial were published in the September, 1942, issue of the “Journal of Agriculture.” As the onions available for the trial had been held in ordinary storage for approximately three months, much experimental work dealing with the state of'the maturity of onions for successful heat curing, and storage could not be undertaken. In addition the season was too far advanced when the experi-

mental chamber was ready for storage, to determine to what extent the development of stem-end rot can be controlled by forced drying or curing directly after onions are harvested. This work will, therefore, form an important part of the trials at the commencement of the coming harvesting season. -

Examination During Storage A heat storage trial was commenced on July 3, 1942. The onions were examined on September 15, and November 20, and replaced in the chamber for a further period of storage. The results of these two examinations are as follows: — The temperature of the experimental chamber was controlled thermostatically at 72deg. to 76deg. F., and the relative humidity at 70 per cent., after the humidity control equipment had been installed and put into working order early in November.

Don't

neglect disease and pests in the orchard. The Department of Agriculture will post you the free bulletin on the control of orchard diseases and pests by spraying.

TABLES SHOWING VALUE OF CAREFUL SORTING BEFORE STORAGE. The sorting was carried out before the onions were placed in storage in July, and the following tables show the losses in the two . sections when re-sorted during the first examination on September 15th. ' . . Section 1: Average method of sorting onions. ’ Section 2: A careful method of sorting for storage. Section 1: Average method of sorting.

A summary of this table shows that in Section 1, where average sorting method was aplied, the loss of onions from deterioration during storage was 1013 onions more than in Section 2,. in which a greater number of defective onions had been detected and rejected when they were more carefully sorted for storage. Storage Conditions The onions held for the trial were stored as follows: ’ (a) In the usual type of onion cental bags stacked three bags high. (b) In the cental bags placed in a timber rack to remove weight from the onions. (c) In a specially designed onion storage crate with dimensions 20in x 16in x 14in. Methods (b) and (c) gave good results; but in (a), where the bags were stacked one on top of the other, the onions, particularly in the lower two bags, became compressed so that the air circulating in. the chamber did not penetrate into the centre of the bags. Diseased onions in the centre of these bags did not dry out properly, as in the other two methods of storage, and caused the surrounding onions to develop root growth. Since the conditions for harvesting last season were unsatisfactory, it was impossible to obtain a perfectly sound line of onions suitable for storage. A careful selection was made from the lines available, but many onions were infected with incipient stages of dis-

ease, and these could not be detected during sorting. In (b) and (c)’methods of storage,, sprouting, root growth, and decay appeared to develop only' in unsound ■onions.The ' trial therefore indicates that with heat storage, sound onions can be kept over until the next season’s onions appear on the market. In the next trial it is hoped to obtain conclusive proof of this indication. Summary The results of the two examinations shows that from 26,800 onions placed in the experimental chamber in July, 21,400 of these were still in . excellent ■marketable condition on November 20. The weight lost during storage and sorting was practically all due to the faulty onions rejected at both examinations. These onions had dried out, and this accounted for almost all of the moisture and weight loss. • The seconds, totalling 1621 onions from the two examinations, are included in, the total onions rejected. ■ These seconds were fit for sale. The cost of erecting the experimental chamber, and installing the equipment was in the vicinity of £2OO. The cost of electric power for maintaining the required storage condition was 4s per ton per month, based on a full chamber, or 32s per ton for eight months’ storage. Arrangements for a further trial during the coming season are now under consideration.

* Onions not-'properly matured which had dried out or shrivelled during storage.

Weight of onions (in lb.) before storage on July 3 .. .. 4,272| Weight before sorting on September 15 3,928 Weight after sorting on September 15 3,4181 Original number of onions .. 26,861 Number of sound remaining onions after sorting on September 15 ' 23,119 Number of sprouts .. .. .. 1,087 Number of rots ■■■ .. 1,106 Number of root growth 56 Number of seconds* .. • 728 Total number of onions rejected on September 15 3,742 Total weight loss after sorting .. ' 853f ■

FIRST EXAMINATION, SEPTEMBER 15, 1942.

Weight (in lb.) on replacing in chamber on September 15 . ... 3,4181 Weight before sorting on November 21 3,102 Weight after sorting on November 21 2,896 Number of onions before sorting 2,896 23,119 ' Number of sound onions after sorting on November 20 ... .. : .. on 21,400 Number of sprouts 1,362 Number bf rots- .. < .. .. ". .. 161 Number of root growth 68 Number of seconds* 128 Total onions rejected ' 1,719 Total weight loss lb 5221

SECOND EXAMINATION, NOVEMBER 20, 1942.

Original number . of , onions, Total remaining sound onions, ... November 20. Total onions < rejected. Original weight, July 3. ; " Weight after ■. . sorting, b November 20. Total loss weight (lb.) ' Total seconds or saleable onions included in itotal onions rejected. 26,860 1 21,400 5,460 - 4,272-1 2,896 , 1,3761 ; 2,896 1,621 1,376 J 1,621

TOTAL LOSS AT BOTH EXAMINATIONS.

No. of onions when placed in storage in July. No, of sound onions following sorting in September. Total defective onions lost. Deterioration from Sprouts. Kots. Root growth. Seconds. 11,781 9,059 ' 2,722 660 1,143 Ill 808 Section 2: Careful method of sorting. 11,580 9,871 1, 709 404 585 12 708 Differences in losses between Sections 1 and 2 1,013 256 558 , . ' 99 100