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