The Sugar Line

Until 1 October, Jeju growers who wanted to ship ultra-early tangerines had to pass an extra test. City inspectors picked ten fruit, and at least eight had to read 8.5 brix or more, a measure of the sugar in the juice. Now the fruit goes straight to the packing houses, and to the test every Jeju tangerine faces there.

There is plenty to test. The province's agricultural research service expects about 443,300 tonnes of open-field tangerines, 7.8 percent more than last year, and rates the fruit's quality the best since its surveys began.

Commercially, a tangerine is whatever a rule says it is. Jeju's citrus ordinance fines anyone who ships or sells fruit that misses the province's product standard; processors buy that fruit at a price set each year. The standard sets a size window and a sugar floor, and sugar can now override size: a tangerine too small to sell counts if it is sweet enough. This is how the line is drawn, who enforces it, what it is worth and what is pushing on it.

For the climate forces redrawing Korea's fruit map, read The Orchard Moves North.

What the rule says

Under the enforcement rule's annex, last amended in October 2024, onju (satsuma) tangerines, the island's main crop, must measure 49 to 70 millimetres across, or weigh 53 to 135 grams, in five classes from 2S to 2L. The sugar floor depends on how the fruit was grown: 8.5 brix for ultra-early open-field fruit, 9.0 for the main open-field crop, 10.0 for greenhouse fruit and fruit ripened through winter under rain shelters. Peel may not stand away from the flesh over half its surface, and no fruit may carry a serious defect, such as rot, artificial colouring or a sunburn scar 1 centimetre wide.

Then comes the clause that changed the rule's character: whatever the size limits say, onju of 10 brix or more count as product when the governor announces it after consulting the growers' citrus committee. On 14 September the committee set the 2026 terms. Fruit from 45 to 49 millimetres may ship if an optical sorter or handheld meter reads 10 brix or more, as may export fruit from 70 to 77 millimetres, and fruit that size grown over reflective ground sheets such as Tyvek if a sorter passes it. In Jeju, a tangerine 47 millimetres across is processing fruit at 9.9 brix and a boxed tangerine at 10.

Hybrid citrus, the late-season fruit sold as hallabong and its relatives, is judged on sugar and acid instead: at least 11.5 brix and at most 1.1 percent acid for hallabong, cheonhyehyang, redhyang and karahyang, 10.0 brix and 1.0 percent for hwanggeumhyang. Those limits apply only once a variety covers 100 hectares on the island.

From size to sugar

The sugar clause is the newest layer of a rule built to keep weak fruit off the market. Today's ordinance dates from 2006. Since 2021 the province has tested ultra-early fruit before harvest, because under-ripe fruit shipped early, it says, drags down trust in all Jeju citrus. In 2022 it changed what happens to rejects: after four years of an on-farm isolation programme, which left an image of 'discarded tangerines' and complaints about the look of tourist areas, it began buying them for processing. In October 2024 the sugar override entered the rule. The island now grades more on taste and less on size.

What the line is worth

Failing has a set price. For 2026, processors pay ₩210 a kilogram for fruit that misses the standard. The province's tables put the average return on the 2025 open-field crop at ₩1,701 a kilogram, so by Ag Digest's arithmetic, fruit below the line earns about an eighth of the average. That crop of 410,965 tonnes grossed ₩699.0 billion.

Ag Digest's archive of settled wholesale auction prices shows the calendar growers sell into. At Seoul's Garak market, mandarins averaged ₩2,854 a kilogram in December 2025, when 11,245 tonnes sold, and ₩8,537 in June 2026, the greenhouse season, when 316 tonnes did: every grade pooled, as retrieved on 5 October 2026. Current prices are on our mandarin and hybrid citrus pages.

Sugar is also how a grower beats the market average. One Seogwipo grower who ships rain-shelter fruit at 16 to 18 brix explained:

Where the trees went

The line shapes planting, too. The province's tables show open-field onju shrinking from 16,775 hectares for the 2015 crop to 13,972 for 2025, and its growers from 22,659 farms to 19,983. More than half of that loss came in one step, between the 2016 and 2017 crops, that the tables do not explain. Over the same decade the four biggest hybrids doubled, from 1,917 to 3,834 hectares: cheonhyehyang from 260 to 1,071, redhyang from 145 to 932, hwanggeumhyang from 76 to 368, with hallabong steady near 1,450.

Hybrids earn more per kilogram (₩3,657 for hallabong and ₩4,801 for redhyang in 2025), but most have been grown under cover, the province says.

Heat raises sugar and scars peel

Weather pushes fruit across the line from both sides. This summer helped sugar: July and August ran 2.0°C and 1.8°C warmer than normal, with far less rain and more sun, and the August survey found sugar at 8.5 brix, 1.4 above the five-year average. It also found more fruit per tree than usual, 909 against 813, and smaller fruit in Jeju City, the island's northern half: 41.9 millimetres, 2.6 below normal.

Heat also scars, and a sunburn mark 1 centimetre wide makes even a sweet fruit a serious defect. The Citrus Research Center of the Rural Development Administration (RDA), as reported by Agriculture, Fisheries & Livestock News, says fruit skin can run 16°C hotter than the air and that the risk climbs once it stays above 46°C for three hours; in its trials, misting at midday cut sunburn from 4.0 to 1.9 percent.

On our reading, a crop of many small fruit leans harder on the 10-brix clause, while heat marks count against even the sweetest. November's survey gives the final volume and defect rate.

Field note: reading a box of Jeju tangerines

• Look for the inspection mark, with variety, origin, weight, size class and shipper.
• Read the size class: 2S to 2L is 49 to 70 millimetres; smaller onju need 10 brix.
• Know the floor: 9.0 brix for the main open-field crop, 10.0 for greenhouse and winter-harvest fruit.
• Check the variety: a hybrid grown on under 100 hectares is outside the hybrid sugar standard.

The Citrus Expo runs from 19 to 23 November in Seogwipo. A question to take there: when every fruit's sugar can be measured, how long should size decide what counts as a tangerine?