Transcript Curing

Curing Regimes for Optimum
Quality and Nitrosamine
Levels in Burley and Dark
Aired-cured Tobacco
Prepared by Christian de Roton
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Air-curing
Two stages
1 - Yellowing
2 - Drying
– Browning
– Stem Drying
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Yellowing
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Stage of leaf transformation
Keep the leaf alive :
– Optimum Temperatures 20 to 25 °
– Extremes T°C 16 - 38 °C
– Optimum relative humidity 80 -85 %
– Extreme RH %
–
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DAC 75% - 85 %
Burley 55% - 85 %
Yellowing
Temperature constraints
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If T°C < 16 °C :
– transformations slow down
– curing duration increases
– loss of quality
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If T°C > 38 °C :
– transformations are definitively stopped
– tobacco is not marketable
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Yellowing
RH% Constraints
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If RH % > 85 % :
– bacterial development
– leaves stick together
– loss of quality
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If RH % < 75 % light DAC
< 55 % Burley
– transformations are definitively stopped
– fixing of green or yellow coloration.
– loss of quality.
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Yellowing
Basical principles
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Favor warming :
– Close the barn nightly
– Use glasshouse effect in plastic
shelters
Open as little as necessary
– close tightly if outside air is too
dry
Clean the air if too wet
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Speeding up the yellowing
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Air-recycling using fan
– during warm hours
– barn slightly open
( sides closed, doors open )
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after fan is off
– remove excessive moisture if
necessary by opening the sides.
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Yellowing
if weather is too cold
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If RH % is sufficient
– Heating with air-recycling - 16 °C max
– fan in the barn
– barn with no air leakage
– excessively low RH % is dangerous .
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Drying
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Two steps :
- Browning of lamina
 - Stem drying
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Optimum RH %
• DAC 60 - 75 %
• Burley 50 - 75 %
Conditions to be complied with for 4 to 6
hours per day
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Drying
RH % Constraints

RH % > 80 % :
– development of moulds
– sticking of leaves
– fermentation of leaf tips
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RH % < 60 % light DAC
< 50 % BEY:
– transformations are stopped
– yellow coloration,if any, is fixed
– loss of quality
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Drying
Suitable conditions
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Open the barn early in the day
Close around 5:00 p.m.
Check curing around 1:00 p.m.
Mind the days with no wind.
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Drying
Bad outside conditions
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Heat and ventilate during 5 to 10 hours
air comes from outside
intervene whenever the day is wet.
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Air - curing
RH %
90
Bacteria
Moulds
85
80
75
Yellowing
70
% HR
65
Browning
60
Stem drying
55
50
Colour fixing
45
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55
53
51
49
47
45
43
41
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
40
days
Heater and fan on the ground
Wet air removal
Recycling
Polyethylen film
damper
Tobacco
Recycling
Heater and fan
Outside
air intake
Ventilation shafts
Length of barn : 50 - 60m max
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Heather and fan at the top
damper
Heater and fan
Outside air
intake
Ventilation shafts
Polyethylen film
Use of warm
air from the
dome
Tobacco
Recycling
Sides slightly
up
Wet air removal
Length of barn function of ventilation power and housing speed.
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Use of heating and
ventilation
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Heating :
– Barn is tightly closed,
– Air comes from inside,
– Monitor RH%.
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Drying :
– Sides closed,
– Wet air removal system open,
– Air comes from outside.
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