Page 8 - Vol.37-No.2

CROP PROTECTION

ing out the chemicals into hot water (the
infusion) for assessment by expert tast-
ers. Results from this ultimate test can be
used to ‘pin-point’ the effect of growing
conditions including soil nutrient status.
This is exactly what has been done
at Tocklai, where tea agronomists, food
scientists and tasters have identified the
significance and exact role of sulphur in
tea quality. Field trials over a six-year pe-
Tea estate at Jorhat in Assam, North riod using a variety of sulphur sources, Picking tea under the hot sun on an
East India (Picture courtesy Omex) including gypsum (calcium sulphate), estate at Jorhat in Assam, North East
ammonium sulphate and micronized el- India (Picture courtesy Omex)
ing Kenya and to a degree that demands emental sulphur gave positive respons-
dedicated sulphur fertilizer. Sulphur was es but only up to a certain level. Sulphur strength, taste, odour and the bright am-
traditionally provided incidentally via up to 40 kg ha/year increased tea yield. ber/red colour of quality liquor, were
nitrogen and potassium fertilizers such A rate of 20 kg/ha/year was the most identified as keys to the quality status
as ammonium sulphate and potassium cost-effective treatment. of tea. They were found in higher con-
sulphate with the sulphur element in the centrations following sulphur applica-
molecule. With the need for sulphur rec- tion with 20kg sulfur/ha giving the best
ognized the fertilizer industry respond- overall result. And there were margin-
ed with design and development dedi- al increases in the flavonol glycosides
cated sulphur fertilizer based on pure such as rutin and quercetin and thought
elemental sulphur formulated as pas- to contribute to a brighter colour and
tilles and prills. The sulphur is degrad- Enhanced flavour of the infusion. The
ed in the soil by Thiobacillus bacteria to contribution of sulphur to the bright, am-
form soluble sulphate that is absorbed ber-red colour of quality black tea liquor
by the root system of the tea bush. is particularly interesting. Sulphur in its
common solid state is a yellow powder.
However, the selective use of tradition- On heating it melts to give bright, am-
al fertilizer with a sulfur component may ber liquid which crystallizes on cooling
still be important. Researchers at the to produce amber crystals with a colour
Tocklai Experimental Station reported and ‘shine’ and uncannily similar to that
how increased problems with sulphur of quality black tea liquor.
deficiency could arise. Problems may
occur when ammonium sulphate (a sul- Selective plucking of the terminal These findings can be related to orig-
phur-containing nitrogen fertilizer) and bud plus three youngest leaves gives inal concentrations of polyphenols in
single super phosphate (a sulphur-con- the highest yield of high quality tea fresh leaves, because theaflavins and
taining phosphate fertilizer) are re- (Picture courtesy Omex) thearubigins are produced by enzyme
placed by urea and rock phosphate, re- controlled oxidative reactions on poly-
spectively, neither of which have sulphur Colour, brightness, strength, body, phenols during fermentation. Polyphe-
in the molecule. nols are heavily concentrated in the
taste and flavour of the tea liquor are ad- youngest growth, terminal bud (28%),
Extra benefit from sulphur fertilizer versely affected by sulphur-deficiency, smallest (first) leaf (28%), second leaf
application comes from sulphur’s addi- but the Tocklai trials went further and (21%) and third leaf (18%). In summary,
tional role as a soil amendment product related changes in these parameters to sulphur deficiency hits hardest at young
to increase soil acidity during tea estate levels of specific chemicals in the leaves. growth (terminal buds and first three
rehabilitation. The tea bush requires an The tea was produced by CTC (crushing, unfurled leaves) selectively plucked for
acid soil with a pH between 4.5 and 5.5 tearing and curling), the most commonly finest grade teas. These have the highest
and will underperform in soils that are used method of ‘rolling’ in the Indian tea concentration of polyphenols converted
too compact or alkaline. industry. Key tea chemicals were mea- during fermentation by polyphenol oxi-
Sulphur and tea quality sured using biochemical analysis and dase enzymes into the all-important tea
HPLC (High Performance Liquid Chro- chemicals responsible for quality liquor.
Everyone knows that correctly dosed matography) of black tea liquors. Tasters
and balanced fertilizer improves crop from J. Thomas & Co Limited in Calcutta
yield and quality. The benefits are gen- were used to assess organoleptic quality.
erally difficult to ‘pin-down’, but tea is Tasters’ scores at 74.0 for tea produced
different. The fresh green leaves are put with 20 kg sulphur/ha were by far the
through a series of exhaustive process- highest, 13.7 higher than no sulphur and
es, including withering, rolling, fermen- a full 10.0 higher than 40 kg sulphur/ha.
tation and firing. This generates and Other objective quality factors showed
consolidates a group of all-important the same trend with brightness and total
chemicals that combine to determine colour responding positively to appli-
tea quality through flavour and aroma, cation of sulphur fertilizer. Two groups Sulphur is a key element in the tea
body, strength, colour and brightness of of chemicals called theaflavins and chemicals which impart colour and
the liquor. Tea processing ends by leach- thearubigins, and responsible for body, f avour to the tea infusion
Circle 5 on enquiry card
6 Vol. 37 No. 2