The effect of Trellis Drying, Harvesting, Handling and Storage on Processability of Dried Vine Fruit.

DRIED FRUITS RESEARCH COUNCIL FINAL REPORT DAV 29F:

The effect of trellis drying, harvesting, handling and storage on processability of dried vine fruit.

Organisation:

Department of Agriculture and Rural Affairs

Project Supervisor:

Mr. R. J. Hayes Sunraysia Horticultural Centre

Time Span:

1987-88 to 1989-90

Objectives 1.

To improve the quality of trellis dried fruit by examining and modifyi ng the harvest and storage aspects leading to poor quality fruit.

2.

Assessment of the damage caused to fruit when harvested using a range of mechanical harvester types.

3.

Assessment of spray coverage and fruit dryin g rates obtained using up to six, highvolume, grower developed wetting machines.

4.

To produce a high quality publication detailing all aspects necessary for production of high quality trellis dried fruit.

Research Report

Year 1 The trial conducted during the 1988 harvest consisted of looking at the effects of different harvesting methods, moisture contents and fruit harvest times on dried fruit damage index levels. Trials were conducted on own rooted H5 sultana vines trellised to a Marshall tee o n the ADFA block at the Sunraysia Horticultural Centre. The trial design was a randomised block with five replications of eight vine plots. Treatments were laid out in a factorial and consisted of two harvest methods (mechanical or hand), three moisture contents for harvest (20%, 17% and 14%) and rwo harvest times (morning and afternoon). Maturity and berry weight were recorded when the canes were cut, as well as moisture content, crown g rade, damage index and hunterlab colour meter readings. Vines were sprayed with a commercial wetting machine on 25th/26th February, 1988 and all canes were cut as soon as spraying was completed on the 26th. It was not possible to

2 harvest fruit exactly at the desired moisture content of 14, 17 and 20 percent and the actual mean harvest moisture contents were 13.2, 14.8 and 17.1 percent. The dried fruit was harvested on the 17th March (13.2%), 21st March (14.8%) and 25th March ( 17.1%) using a Shaw harvester and finish dried on groundsheets in the normal manner. Samples were stored in sweat boxes for six months, processed and packed into 15kg cartons on the small scale CSIRO processing line and stored at ambient temperature for a further 12 months. Damage indices (Simmons and Lewis, 1978) were recorded after harvest, after six months storage, after processing and after a further 12 months storage. The result were analysed by analysis of variance to determine whether there were any significant interactions between harvest moisture content, time or method. Results and Discussion Some concern existed that maturities would vary between oial plots which may have caused variations between drying rates or final fruit quality. However, fruit maturity and berry size were quite uniform throughout the triaf (Table 1). Table 1

Soluble solids (0 Brix) and average berry weight at cane cutting for each trial plot. Means of 12, 100 berry samples.

PLOT 1

2

3

4

5

Soluble Solids 0 ( Brix)

23.0

22.8

22.5

22.7

22.0

Average Berry Weight (g)

1.75

1.65

1.62

1.60

1.48

Damage Levels: 1.

After Harvest As expected, damage index levels at harvest were all extremely low with most treatments close to the base damage index level of 33 (Figure 1). Machine harvesting always caused higher damage levels than the corresponding hand harvest treatment, with the differences being significant for early harvest at 14.8% m.c. and late harvest at 17.1 % (P=0.05). There were no significant differences between early and late harvest for either harvest method within any of the moisture contents or between moisture contents (P=0.05).

3 2.

After six months All damage index levels remained low after six months, and only increased slightly from the levels at harvest (Figure 2). Any increase in damage index is probably due to sugars leaching out of berries during storage. The only significant difference between treatments was with early and late harvest at 13.2% (P=0.05). The difference between these treatments was due to an increase in damage of the late harvest for bo th hand and mechanical treatments. There is no apparent reason for this increase being larger than for any of the other treatments. In practical terms, the damage index levels for any of the treatments either at harvest or after six months would be regarded as negligible by any dried vine fruit packers.

3.

After processing The damaging nature of dried vine fruit processing is clearly shown with the higher damage levels for all treatments after processing (Figure 3). While these figures are high it is also worth noting that damage index levels on commercially processed fruit frequently reach 80 and above. There is a definite trend toward higher damage levels for fruit harvested at higher moisture contents, despite the damage levels being similar for all treatments before processing. Once again the differences between hand and mechanical harvesting are small while the higher damage levels on fruit harvested at higher moisture contents would be expected due to softer skins on the berries making them more susceptible to damage.

4.

12 months after processing Damage levels increased again for all samples, presumably due to leaking of sugars during storage (Figure 4). The earliest harvested treatments at the lowest moisture content (13.2%), had significantly less damage (for hand or mechanical harvest) than any other treatment (P=0.05). While mechanically harvested treatments had higher damage levels than the corresponding hand harvest treatment in all but one case, none of the differe nces were significant.

Conclusions Based on this single year 's data, early morning harvest of frui t which was about 13% m.c. would give minimal damage, while the type of harvest system used would have no significant effect on the level of damage sustained. Mechanically harvested fruit almost always had higher damage levels than hand harvested fruit, however the differences were always small and s.hQuld not cause quality differences in processed dried vine fruit. '

40.0

V)

~ c:

3 0.0

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c

Late

Early

13.2% Figure 2.

Late

Early

17.1%

14.8%

Nean damage ind ex after six months storage for sultanas harvested at three different moistur-e cont.en l s, two diff e rent times and by two harvest meth ods. I = standard error of mean.

cv

01 0

E

50.0

0

0

40 .0

30.0

Ear ly

Late 13.2%

~ Hand Harvested Figure 1.

Early

Late

14.8% Hdrvest Time

Ear ly

12:3

La te

Machine Horv-ested

Mea n damage index at harvest for sultanas harv este d at three di[[erenl moisture content , two di[(erent times and by two Harvest n1et hods . 1 = standard error ol mean.

80.0

70 .0 l.{) ~

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60.0

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Ol CJ

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50.0

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a

40.0

Late

13.2%

bS:SJ Hand Harvested Figure 3.

Early

Late

14.8%

Harvest Time

Early

Late

17.1%

EZd Machine Harvested

Mean damage index for s ul tanas proc ess ed after six mont l1 s storage and ha rvested at thre e different moisture contents, two dirfe~ent times and by two harvest met hod s . I = sta ndard e rror of mea n .

80.0

70.0

11 c: ::J X

60.0

(l)

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01

0

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Early

Late 13.2.%

(.S3 Hand Harvested Figure 4.

Early

Late

14.8% Harvest Time

Early

Late 1'7.1%

EZl

Machine Harvested

Mean damage index [or su l tahas sto red Eor six months, processed and stored [or a furtl1cr 12 monLhs after initial l y being harves t ed at t h ree different moisture contents, two different times and by tHo harvest methods. 1 = stan dard error of mean.

4 The damaging nature of dried vine frui t processing on final fruit quality has been clearly highlighted.

Year 2: Work on this project was designed to repeat the 1987/88 trial as it was necessary to collect at least another year's trial data. However due to the poor drying conditions in the latter half of the drying season, this trial could not proceed as planned. Some fruit was harvested from the trial plots, but the amount of damage incurred due to the rain prevented any realistic comparison between treatments. Nevertheless, work was undertaken to assess the effect of different harvester types on damage levels 6f dried sultanas. The harvesters examined were Shaw, Upright and Mecca machines. All were harvesting fruit late in the season which was typically between 25-30% moisture content. Damage to most fruit was negligible at moisture contents below 26%. Shaw harvesters caused large amounts of damage to fruit harvested at about 30% (Table 2). The average moisture content is probably not as important as the moisture content of the wettest berries, which are easily damaged and spread sugar around. Table 2

Moisture content and damage index for trellis dried fruit harvested with five different mechanical harvesters (average of four samples).

HARVESTER TYPE

MOISTURE CONTENT AT HARVEST (%)

DAMAGE INDEX

Shaw l Hand

26 26

38 39

Shaw 2 Hand

30 31

45 37

Mecca Hand

27 27

44 44

Upright 1 Hand

26 26

37 36

Upright 2 Hand

23 23

37 37

:

~.

5 The damage index is useful in determining damage caused by harvesting, and should be used in conjunction with a count of the number of berries with leaf adhering as a means of assessing damage. From the limited observations undertaken it seems that Upright harvesters may be able to harvest fruit at a higher moisture content before damage occurs compared with Shaw harvesters. This may be because the Upright has two pairs of beaters and so dissipates energy over a wider area, with a consequent lower maximum force on berries.

Year 3: Work on this project was limited due to the resignation of Mr. R. Mattschoss. Mr. Mattschoss had been appointed project supervisor when Mr. R. Hayes became Leader of . the Viticulture Section at Irymple. Because of Mr. Mattschoss's resignation, project work on the assessment of spray coverage using high volume, grower-developed wetting machines did not proceed, and funds were returned to the DFRC. The major work area proceeded with in year 3 has been towards the production of a high quality publication on trellis drying. This focuses on trellis drying as a total production management system and also on trellis drying as a salvage measure. There has been an increase in demand for information on trellis drying in recent years, partly due to difficulty in obtaining harvest labour and also due to rainfall experienced during harvest. This publication is currently being rewritten to focus more on the Shaw Trellis system (S.T.S.) and will include chapters on installing the S.T.S.: conversion options to the S.T.S.; managing the S.T.S., and a list of components .and prices for variants of the S.T.S. The publication should be available in June or July 199 1.

Reference Lewis, W.J. and Simmons, I.D. 1978. A test for skin damage of dried grapes. Food Tech. Aust. 30, lQ, 391-2. 0023WN.036