As we approach the end of the first month of the new year, it is timely to look at the harvest seasons of tea and how it affects the taste and value of our favorite beverage.
To begin, it is useful to look at the 24 Solar Terms of the Chinese Agricultural calendar in the table below which was believed to be first in use during the Spring Autumn Warring states (722–481 BC). This was based on the position of the sun and provided useful markers for farmers.
The cells in yellow denote the start of each season in China, while the green cells denote the mid-point. These 8 markers form an accessible skeleton to view the entire calendar.
English Chinese Date Remark
Minor Chill 小寒
Jan-06
Temperature falls significantlyMajor Chill 大寒
Jan-20
Coldest period of the yearSpring Begins 立春
Feb-04
Beginning of springRain Water 雨水
Feb-19
Rain starts to replace snowInsects Awaken 惊蛰
Mar-06
Insects awake from hibernationVernal equinox 春分
Mar-21
Mid SpringClear bright 清明
Apr-05
Ample sunlight for plants to growHarvest rain 谷雨
Apr-20
Ample rain for grains to growSummer begins 立夏
May-06
Beginning of summerGrain full 小满
May-21
Wheat grains are plumpGrain in ear 芒种
Jun-06
Wheat is ready for harvestSummer Solstice 夏至
Jun-21
Mid SummerMinor heat 小暑
Jul-07
Temperature rises but has not peakedMajor heat 大暑
Jul-23
The hottest period of the yearAutumn Begins 立秋
Aug-08
Beginning of AutumnHeat’s Limit 处暑
Aug-23
Temperature starts to fallWhite Dew 白露
Sep-08
Temperature falls, morning dew accumulatesAutumnal equinox 秋分
Sep-23
Mid AutumnCold dew 寒露
Oct-08
Dew starts to crystalizeFrost Appears 霜降
Oct-23
Frost appearsWinter Begins 立冬
Nov-07
Beginning of WinterMinor snow 小雪
Nov-22
Snow fallsMajor snow 大雪
Dec-07
Snow accumulates on the groundWinter solstice 冬至
Dec-22
Mid WinterAs with virtually all the content on this site, this post is written with a Chinese and Taiwanese focus. Typically, teas harvested before ‘grain full’ is considered spring tea, those before the first ten days of August are summer teas, tea harvested before last ten days of October are autumn teas and thereafter, winter teas.
Impact of Harvest Season
Typically, spring tea is the most highly valued season for tea. This is not due to blind adherence to tradition or limited supply- in fact spring harvest forms the bulk of the annual harvest, for example 40-45% of all Tieguanyin- but an empirical superiority, as we will look at later.
The tea plant typically ceases budding at temperatures of 10⁰C and below, but during this time it continues to accumulate nutrients. Hence during winter through early spring, when tea plants cease budding, or even hibernate for northern areas, the accumulation of nutrients is higher.
In addition, plants need heat, rainfall and sunlight to grow. Take for example the average temperature climate of Hangzhou, home of the excellent Xihu Longjing, as shown in the table below
Annual Average Temperature of Hangzhou[1]
Avg Low Avg High Avg Precipitation
January 2°C 8°C 6.56 cm
February 3°C 10°C 6.49 cm
March 7°C 14°C 10.53 cm
April 12°C 20°C 8.87 cm
May 17°C 26°C 9.84 cm
June 22°C 29°C 17.06 cm
July 25°C 33°C 12.91 cm
August 25°C 32°C 13.11 cm
September 21°C 28°C 8.36 cm
October 15°C 23°C 4.4 cm
November 9°C 17°C 4.25 cm
December 4°C 11°C 3.99 cm
During spring, average temperatures are more moderate as compared to summer and autumn. Coupled with less intense sunlight, the tea leaves grow slower and accumulate more nutrients.
At the same time, the difference in temperatures during night and day is usually greater during spring than it is in summer. Consequentially, the plant grows slower during spring as the cumulative heat it receives in the summer night is higher, which accelerates its growth.
Accentuating the difference is that for most parts of China, other than south eastern China- i.e. Fujian, Guangdong and by the same token, Taiwan- teas are not harvested in winter. When the temperature falls below 10°C, the tea plant stops budding, but it continues to accumulate nutrients. Hence, a spring tea could have 4-6 months period of accumulating nutrients compared to 2 months for a summer tea.
When you add up these factors, the differential in the nutrients in the seasons is sizeable.
Let us look at a numerical illustration.
One of the most important factors in determining the taste of tea is the ratio of amino acids to Polyphenols. In a nutshell (if you want the details, read this), the sweetness and briskness of amino acids should be high enough to offset the bitterness and astringency of polyphenols to provide a pleasant, textured, refreshing drink.
The table below shows 1 bud 3 leaves stalks of a Longjing tea compared through the seasons:[2]
Season
L-Theanine
Others
Total Amino Acid
µg/g
%
µg/g
%
µg/g
%
Spring 8,019
100%
7,683100%
15,702100%
Summer 2,414
30%
3,30443%
5,71836%
Autumn 2,394
30%
4,79762%
7,19146%
As shown above, there is a stark contrast between the amino acid content of spring teas as compared to the other 2.
This is why teas such as Silver Needles which are reliant on L-Theanine for the brisk, sweetness is only made from spring teas.
At the same time, sunlight induces the accumulation of polyphenols (Catechins) in summer and autumn teas. The table below shows the content of various polyphenols of 1 bud to 2 leaves pickings over the different seasons.[3]
Mg/g L-EGC D,L-GC L-EC + D, L-C L-EGCG L-ECG Total %
Spring
8.26
3.93
7.86
50.66
28.52
99.23
60%
Summer
22.44
5.44
11.16
99.93
34.52
164.49
100%
Autumn
25.91
7.38
11.55
67.21
29.75
141.8
86%
For fragrance compounds, the story is the same. Researchers took 100g of leaves with 1 bud to 2 leaves ratios and tested the fragrance compounds in them. It was tested that spring’s harvest had 5.8 mg to 2.4 mg for summer and 4.0 mg for autumn.[4]
Hence, from the data given, it is pretty clear that spring tea is superior to autumn and summer rounds up the cellar. While it is true that there are mitigating factors, for example shading- such as surrounding trees or the slopes of the hills- can reduce the astringency in summer, and indeed all, teas, the base differential is not easily negated.
Exceptions
Summer teas typically fetch the lowest price- in fact the more reputable green and oolong tea producers generally use the summer pickings for tea bags or other low yield products instead of ruining their reputation with inferior products.
However, in recent years an interesting trend is that many producers start using their summer teas for making black tea. Black tea has a lower amino acid to polyphenol ratio as compared to others, hence the falloff in drinkability is not so marked. Furthermore, most of the Catechins are oxidized to compounds such as theaflavins (TFs) and thearubigins which are brisker and sweeter compared to polyphenols. This coupled with the fact that heat and humidity during summer accelerates the oxidation process in producing black tea, allows summer teas to be more palatable when used in black tea.
Another notable exception is autumn Tieguanyin. Interestingly enough, though fragrance compounds are generally higher in spring teas compared to others, certain compounds like linalool and phenethyl alcohol which elicits a floral fragrance, are highest in autumn harvest. This is why autumn Tieguanyin for is generally quite well-received by tea lovers, which together with its more limited harvest, gives it a higher value than other autumn teas.
Information in this article researched and obtained from the following excellent publications:
1) 茶叶生物化学edited by 宛晓春 published by中国农业出版社
2) 茶学概论edited by 周巨根 et al published by 中国中医药出版社
3) 乌龙茶审评 edited by张木树 published by厦门大学出版社
4) 名优茶叶生产与加工技术 edited by 骆耀平 published by中国农业出版社
[1] Table extracted from http://weather.sg.msn.com/monthly_averages.aspx?wealocations=wc:CHXX0044&q=Hangzhou%2c+CHN+forecast:averagesm
[2] Data extracted and translated from 茶叶生物化学edited by 宛晓春 published by中国农业出版社 page 143
[3] Data extracted and translated from 茶叶生物化学edited by 宛晓春 published by中国农业出版社 page 109
[4] Research data extracted and translated from 茶学概论edited by 周巨根 et al published by 中国中医药出版社page 100
