Spend enough time around tea in Northern Thailand and two numbers begin appearing everywhere: 12 and 17.
Oolong No.12 and Oolong No.17 are now familiar names across the tea-growing mountains of Chiang Rai. They appear on farm signs, factory bags, tea menus and product labels, and both have become closely associated with the modern Northern Thai oolong industry. Yet they are distinct cultivars with different parentage, characteristics and processing potential.
The proper name of TTES No.12 is Jin Xuan, 金萱, while TTES No.17 is Bai Lu, 白鷺, usually translated as White Egret. Both were developed by Taiwan’s official tea research programme, now known as the Tea and Beverage Research Station. The station records No.12 as being formally named in 1981 and No.17 in 1983.
TTES No.12, Jin Xuan, was bred from Tainung No.8 and Ying Zhi Hong Xin. Taiwan’s research station describes it as a vigorous, high-yielding small-leaf cultivar particularly suitable for oolong and pouchong production. It also notes one characteristic for which Jin Xuan has become famous internationally: the finished tea can naturally display a milk-like aroma.
That is where the familiar term Milk Oolong comes from. Properly made Jin Xuan does not require milk flavouring to create that creamy impression. Some commercially flavoured teas certainly exist, but the natural softness and creamy aromatic quality associated with good Jin Xuan can come from the cultivar, growing environment and processing itself.
In Northern Thailand, No.12 has proved particularly versatile. It is commonly encountered as a tightly rolled, partially oxidised mountain oolong, where it can show floral, creamy and fresh vegetal characteristics, but that familiar expression is only one possibility. Our Mountain Spice Oolong No.12 GABA takes the same cultivar through GABA processing, while Thai Red Oolong No.12 Open Leaf demonstrates how far No.12 can move from the classic pale rolled-oolong style.
This leads to an important distinction: No.12 is a cultivar, not a tea type. The plant provides the raw material, but the finished tea depends on what happens after harvest. Withering, bruising, oxidation, rolling and drying can take the same cultivar in very different directions.
TTES No.17, Bai Lu, has its own identity. Taiwan’s Tea and Beverage Research Station records it as a cross between Tainung 335 and Tainung 1958. It is also a small-leaf cultivar, but the station describes No.17 as particularly early budding, vigorous, strongly drought resistant and notably rich in fine hairs on its young shoots. It is suitable for oolong production and other more oxidised styles.
Those agricultural characteristics help explain why No.17 found a useful home outside Taiwan as well. In Northern Thailand, it became one of the cultivars adopted as commercial tea production expanded and Taiwanese processing knowledge became more influential.
For the drinker, however, the comparison is more complicated than simply saying that No.12 is creamy and No.17 is stronger. Cultivar matters, but altitude, harvest season, weather, leaf maturity and processing can alter the cup dramatically.
Our Oolong No.17 shows the cultivar in a more recognisable Northern Thai oolong expression. But No.17 can also be pushed much further. Jungle Ruby Black Tea uses No.17 and No.12 material in fully oxidised black-tea production, producing something visually and aromatically far removed from the pale rolled oolongs many drinkers associate with the same plants.
This is why the cultivar number on a tea label should be treated as useful information, not a complete description of the tea. A comparison with grape varieties is helpful. Knowing the grape tells you something about the raw material, but not everything about the vineyard, vintage or winemaking. Tea works in much the same way.
No.12 and No.17 carry genetic characteristics that influence growth, leaf structure, aroma and processing potential. The tea maker then decides how those characteristics will be expressed.
Broadly speaking, Jin Xuan No.12 is particularly associated with softness, floral character and its naturally creamy aromatic quality. No.17 is an earlier-budding cultivar with strong growth, abundant leaf hairs and good resistance to drought and pests. Taiwan’s own research programme lists both among cultivars suited to partially fermented teas, while specifically noting that No.12 can also work well in fully fermented tea production.
Once these cultivars arrived in Northern Thailand, however, they entered a very different environment from the one in which they were developed.
Chiang Rai has its own altitudes, monsoon cycle, soil conditions, harvest seasons and factory traditions. The cultivars may be Taiwanese in origin, but the tea in the cup is increasingly a product of Northern Thailand.
That distinction is important to us at PRANIT.
On our own farm in Chiang Rai we are planting Oolong No.12 alongside Thai Assamica. The two represent very different parts of the region’s tea story: Assamica belongs to the older large-leaf tea landscape of the north, while No.12 represents the later arrival and adaptation of Taiwanese tea genetics and processing knowledge.
Across the wider region, that interaction has become increasingly creative. A cultivar originally selected for oolong production can become GABA tea, highly oxidised red oolong, or even black tea. What began as imported plant material is being interpreted through a different landscape and a different generation of tea makers.
This is also why talking about Northern Thai tea only in terms of whether it is “like Taiwan” eventually becomes limiting.
Taiwan provides the genetic and technical heritage behind cultivars such as No.12 and No.17. That history should be acknowledged clearly. But once those plants have been cultivated in Northern Thailand for decades and processed according to increasingly local practices, the finished teas begin to tell another story as well.
The most useful question is therefore not simply which is better, No.12 or No.17?
It is: what has the grower and tea maker done with them?
A spring Jin Xuan, a more heavily oxidised open-leaf No.12, a rolled No.17 and a fully oxidised black tea made from the same cultivar family can taste remarkably different.
That range is one of the defining characteristics of modern Northern Thai tea.
The numbers 12 and 17 tell us where the plants came from.
What happens next tells us where Northern Thailand is taking them.