Food & Drink Magazine

Harvest Season of Teas and Its Impact

By Dchew78 @peonyts

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 significantly

Major Chill 大寒

Jan-20

Coldest period of the year

Spring Begins 立春

Feb-04

Beginning of spring

Rain Water 雨水

Feb-19

Rain starts to replace snow

Insects Awaken 惊蛰

Mar-06

Insects awake from hibernation

Vernal equinox 春分

Mar-21

Mid Spring

Clear bright 清明

Apr-05

Ample sunlight for plants to grow

Harvest rain 谷雨

Apr-20

Ample rain for grains to grow

Summer begins 立夏

May-06

Beginning of summer

Grain full 小满

May-21

Wheat grains are plump

Grain in ear 芒种

Jun-06

Wheat is ready for harvest

Summer Solstice 夏至

Jun-21

Mid Summer

Minor heat 小暑

Jul-07

Temperature rises but has not peaked

Major heat 大暑

Jul-23

The hottest period of the year

Autumn Begins 立秋

Aug-08

Beginning of Autumn

Heat’s Limit 处暑

Aug-23

Temperature starts to fall

White Dew 白露

Sep-08

Temperature falls, morning dew accumulates

Autumnal equinox 秋分

Sep-23

Mid Autumn

Cold dew 寒露

Oct-08

Dew starts to crystalize

Frost Appears 霜降

Oct-23

Frost appears

Winter Begins 立冬

Nov-07

Beginning of Winter

Minor snow 小雪

Nov-22

Snow falls

Major snow 大雪

Dec-07

Snow accumulates on the ground

Winter solstice 冬至

Dec-22

Mid Winter

As 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%

   7,683

100%

   15,702

100%

Summer    2,414

30%

   3,304

43%

   5,718

36%

Autumn    2,394

30%

   4,797

62%

   7,191

46%

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


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