Curing Regimes for Optimum Quality and Nitrosamine Levels in Burley and Dark Aired-cured Tobacco Prepared by Christian de Roton

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Curing Regimes for Optimum Quality and
Nitrosamine Levels in Burley and Dark Aired-cured
TobaccoPrepared by Christian de Roton
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Air-curing

• Two stages
• 1 - Yellowing
• 2 - Drying
• Browning
• Stem Drying

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Yellowing

• Stage of leaf transformation
• Keep the leaf alive
• Optimum Temperatures 20 to 25
• Extremes TC 16 - 38 C
• Optimum relative humidity 80 -85
• Extreme RH DAC 75 - 85
• Burley 55 - 85

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YellowingTemperature constraints

• If TC lt 16 C
• transformations slow down
• curing duration increases
• loss of quality
• If TC gt 38 C
• transformations are definitively stopped
• tobacco is not marketable

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YellowingRH Constraints

• If RH gt 85
• bacterial development
• leaves stick together
• loss of quality
• If RH lt 75 light DAC
• lt 55 Burley
• transformations are definitively stopped
• fixing of green or yellow coloration.
• loss of quality.

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Yellowing Basical principles

• 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

• Air-recycling using fan
• during warm hours
• barn slightly open
• ( sides closed, doors open )
• after fan is off
• remove excessive moisture if necessary by opening
  the sides.

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Yellowingif weather is too cold

• 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

• Two steps
• - Browning of lamina
• - Stem drying
• Optimum RH
• DAC 60 - 75
• Burley 50 - 75
• Conditions to be complied with for 4 to 6 hours
  per day

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DryingRH Constraints

• RH gt 80
• development of moulds
• sticking of leaves
• fermentation of leaf tips
• RH lt 60 light DAC
• lt 50 BEY
• transformations are stopped
• yellow coloration,if any, is fixed
• loss of quality

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DryingSuitable conditions

• Open the barn early in the day
• Close around 500 p.m.
• Check curing around 100 p.m.
• Mind the days with no wind.

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DryingBad outside conditions

• Heat and ventilate during 5 to 10 hours
• air comes from outside
• intervene whenever the day is wet.

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Air - curing
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Heater and fan on the ground
damper
Outside air intake
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 Use of heating and ventilation

• Heating
• Barn is tightly closed,
• Air comes from inside,
• Monitor RH.
• Drying
• Sides closed,
• Wet air removal system open,
• Air comes from outside.