11. HARVESTING

11.1 Production seasons and Productivity
11.2 Picking of fruits
11.3 Grading
11.4 Post-harvest handling
11.5 Processing of longan

11.1 Production seasons and Productivity

Flowering of longans is quite early in Thailand compared to those grown in other countries like China, Taiwan Province of China and Queensland (Table 2). In Thailand, flowering commences in late December to late February, while in China and Taiwan Province of China longan flowers from late February to early April. In the Southern Hemisphere such as in Queensland flowering commences in August to October and October to November, depending on location. Harvest in Thailand is from late June to late August whereas harvest in China is from late July to late September. In Queensland longan can be harvested from mid-January to mid-March and late February to early April, depending on location.

Table 2. Flowering and harvesting seasons of longan-growing locations

Country	Flowering Season	Harvesting Season
Thailand	Late December - Late February	Late June - Late August
China	Late February - Early April	Late July - Late September
Taiwan Province of China	February - April	July - October
Australia	August - October (North Queensland) October - November (Southeast Queensland)	Mid-January to Mid-March Late February to Early April

In Thailand the marcotted longan tree starts bearing in the fourth year after planting. The yield in the fifth year is about 2 - 5 kg per tree, and this yield increases to 20 kg per tree in the seventh year. In the tenth year, the yield is 60 kg per tree and this increases to about 100 - 190 kg per tree in the fifteenth season. After fifteen years, the yield is in the range of 150 - 200 kg per tree and this figure will last for the next ten years. The yield starts to decline when the tree is over thirty five years old. However, there is considerable variation in yield from year to year and biennial bearing occurs in most cultivars. For mature trees of 12 to 15 years of age, the yield averages one poor crop, one fair crop and one excellent crop over three years. Small fruited, inferior types are reputed to bear more heavily (300 - 400 kg) and consistently.

In term of productivity on a per hectare basis, yield ranges from a high of 7,325 kg/ha/year (1990) to a low of 2,512 kg/ha/year (1989). The productivity varies from year to year and the biennial bearing phenomenon is clearly seen in these yields (Table 3). For example, 1989, 1991, 1993 and 1995 were 'off years when productivity was low. These are alternated with 'on' years such as 1990, 1992, 1994 and 1996 when productivity was high.

Table 3. Productivity of longan as affected by years of production in Thailand

Year	1989	1990	1991	1992	1993	1994	1995	1996	1997	1998
Yield (kg/ha/yr)	2,512	7,325	3,756	6,137	3,375	6,269	4,137	6,175	5,500	5,730

Source: Subhadrabandhu and Yapwattanaphun (2000a).

Table 4. Productivity of longan as affected by locations in Thailand (1993)

Province	Lamphun	Chiang Mai	Chiang Rai	Nan	Phra Yao	Lampang	Phrae	Chanthaburi
Yield (ks/ha/yr)	3,712	6.837	5.194	8.400	4,512	6.287	3.006	2,625

Source: Subhadrabandhu and Yapwattanaphun (2000a).

· Inferior longan cultivars, although Thai material was originally derived from China,

· Greater emphasis is placed on lychee production over longan production, and

· Longan is grown on poor sites with shallow soils in hillsides and foothills, with no irrigation and little or no pest management; this is true for longan in Guangdong.

Table 5. Productivity of longan as affected by years and locations in China

Province	GUANGXI
Year	1987	1989	1991	1993	1995	1997
Yield (kg/ha/yr)	2,435	1,385	923	751	978	634
Province	GUANGDONG
Year	1987	1989	1991	1993	1995	1997
Yield (kg/ha/yr)	2,506	1,758	1,364	1,429	1,004	1,043
Province	FUJIAN
Year	1987	1989	1991	1993	1995	1997
Yield (kg/ha/yr)	1,650	1,700	1,559	1,023	1,301	1,160

Source: Liu and Ma (2000).

Productivity on a per hectare basis ranges from a high of 12,701 kg/ha/year (1995) to a low of 4,506 kg/ha/year (1996) (Table 6). These figures are far superior to those in China and comparable, if not much higher, than those in Thailand. Since the productivity on a per plant basis is comparatively low, the higher production on a per hectare basis can be explained by the higher tree density in Taiwan Province of China. Tree densities of 300 to 600 trees per hectare are found in Taiwan Province of China compared to the lower figures of 195-300 in China and about 50 in Thailand. Alternate bearing phenomenon is very clearly seen in the productivity figures in Taiwan Province of China. The 'off years (1994,1996 and 1998) alternate with the 'on' years (1995 and 1997).

Table 6. Productivity of longan as affected by years in Taiwan Province of China

Year	1994	1995	1996	1997	1998
Yield (kg/ha/year)	9,284	12,701	4,506	11,058	4,637
Yield (kg/plant/year)	26	36	14	32	14

Source: Yen (2000).

Yields of 40-50 kg per tree have been obtained for six to eight years old trees in Australia.

11.2 Picking of fruits

Longan takes about 5 months from blooming to harvest. The fruits are non-climateric and have to be harvested when ripe. Maturity is determined by fruit shape, skin colour and taste. Immature fruits are tasteless. The mature longan fruit has a dark, smooth skin, the inside of which is netted and tastes sweet. Longan trees should be picked twice at an interval of 7 - 10 days. Most cultivars lose flavour if harvesting is delayed, when fruits are mature. The whole panicle of fruits with one or two leaves is cut with a knife or scissors. Removal of too much leaves and wood with the fruit panicles at harvest reduces flowering in the next season. Panicles should not be dropped. They are sorted for size, insect damage and skin blemishes and bunched in a bulk tray. In Thailand, longan fruits with stalk intact (about 21-22 kg) are packed in 35 cm x 50 cm round woven bamboo baskets lined with longan leaves. Stalked fruits are reputed to remain fresher than separated fruits after harvest. Fruit for export, often detached from the panicles, may be packed in corrugated boxes or plastic baskets. It is recommended that fruit should not be picked during rainy weather as this increases the risk of breakdown after harvest.

11.3 Grading

The Thai farmers have established grading of longan fruits into Grades A, B and C. The Grade A fruits consist of 55-75 fruits per kg (14-18 g per fruit), Grade B consists of 76-80 fruits per kg (12.5-13.2 g per fruit) and Grade C consists of more than 80 fruits per kg which encompasses most small-fruited seedling types (Subhadrabandhu, 1990).

11.4 Post-harvest handling

Because of the high sugar content, longan fruit has a short shelf-life. Under ambient temperature (25°-31°C) harvested longan fruit rind turns brown within 3-4 days, and the aril turns rotten within a week and loses its commercial value. An extended few days of keeping is possible when temperature is lowered to 18°C. Prior to storage longan fruit can be subjected to hydrocooling or forced air cooling which can lead to longer storage duration when combined with low storage temperature. To prevent fungal growth on the fruit surface during storage, the fruit can be fumigated with sulphur dioxide. Short term sulphur dioxide fumigation combined with low storage temperature is currently considered to be the ideal and practical method of storage of longan fruit. Fumigation of sulphur dioxide for 20 minutes and storing the 'Shixia' longan fruits at 4°C produced 100 percent of good fruits after 28 days of storage without chilling injury (Han et al., 2000). However, improper handling can cause high sulphur dioxide residue and reduce the flavour of the aril. Sulphur dioxide fumigation can affect both the external as well as the internal qualities of the longan fruit.

In a study on the shelf-life of cold-stored longan fruits, Lin et al., (2000) reported that longan fruits which have been fumigated with sulphur dioxide and then packed in polychloroethylene (PE) film (0.03 mm thick) bags and stored at 3°C for 46 days are able to retain the original skin colour and aril eating quality when moved out of cold storage to room temperature for as long as 78 hours. When the fruits were moved out of cold storage an oxidation retardant was added to them.

Sulphur dioxide injury to the rind depends on the application concentration and the fumigation period (Tongdee, 1992). Injury to the rind occurs at intermediate concentrations. There is an important balance between the amount of sulphur dioxide applied, the sorption of the fruit and the residual sulphur dioxide detected on the fruits.

Recent studies showed that modified atmosphere storage (50 percent air + 50 percent nitrogen) of longan fruits treated with antifungal agent resulted in a 92.3 percent marketable fruit ratio and high percentage of nutrient composition in fruits stored at 24° - 26°C for seven days (Liu and Ma, 2000).

11.5 Processing of longan

Due to the short shelf-life of fresh longan fruits, their uses can be extended by processing them into various products. In Thailand, the longan fruits have been processed into canned longan, dried 'longan nuts', longan nectar and frozen longan (Subhadrabandhu, 1990). There are substantial canning factories for longan in Thailand, China and Taiwan Province of China. Large fruits are generally used for canning. The cultivars 'Biew Khiew' and 'Daw' are preferred for this purpose in Thailand. Due to the high brix content, little sugar additive is required as the fruits are canned in their own juice. It is believed that canned longan retained their individual flavour better than 'rambutan' and lychee.

Subhadrabandhu (1990) has described in detail the processing of longan into dried fruits in Thailand. According to him longan fruits are dried either intact or with pericarp removed. Small and medium fruits are used for drying. The process of drying longan fruits can be done by boiling the fruit for five minutes, followed by sun or oven drying at 55°C. When the fruits start to dry the temperature is raised to 70°C until they are completely dried. The total drying period is 19-20 hours. Dried intact fruits can retain better their flavour and aroma when compared to fruits which have been dried without the pericarp. The dried longan fruits contain moisture of about 18-19 percent and have very high sugar content of 60-65° brix.