Flue-Cured Tobacco basic overview

[FmGrowit]

Curing

Immediately after harvest, the leaves are placed into metal racks or boxes for curing. Heated air is forced through the tobacco to cause it to first turn yellow or orange in color, and then to dry the leaves and stems. The initial temperature for yellowing the leaves is 95 to 100 degrees F, and is then increased incrementally to 165 or 170 degrees. Ventilation is part of the curing process and is varied as needed to remove moisture while retaining quality of the tobacco. It takes five to seven days to cure a barn of tobacco, and six to nine curings may be made in each barn in a season. After the tobacco is cured, moist but unheated air is forced through the tobacco to cause the leaves to become pliable enough so they will not shatter during the unloading process.


by; E. B. Whitty, professor emeritus, Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

 

[BigBonner]

I will be setting my last acre of tobacco today it will be mainly flue cured just to see if I can grow it .
I will have to figure out how Im going to cure it . Im not set up with the flue barns and heaters .

Any sugestions ?

 

[FmGrowit]

Larry, with the way the season has been going this year, I'd say it's still worth setting the plants. I spoke with a Broadleaf grower in Massachusetts and things are just as bad up there. They've had "no spring this year". If the supply of leaf is lower than what the industry needs, the price has to go up.

Check with Tobacco Quarterly, there might be portable curing barns available. The biggest problem with Flue curing is the need for a heat exchanger now...they test for exhaust gases on the leaf, so gas burners in the barn doesn't work anymore.

 

[FmGrowit]

Larry, This is another pretty big file, but it has the numbers for curing on page 60 - 63.

http://pubs.ext.vt.edu/436/436-048/436-048_pdf.pdf

Let me know when you're ready for some help.

 

[deluxestogie]

Here are two 1878 drawings of a flue-curing barn:

What's worth noting is that the flue(s) from the heat source are gradually sloped from near the bottom of the barn, and do not rise vertically until they exit the wall. The fire pits are bricked in. Flue-curing barn fires were, not surprisingly, common back then.

If you put a heat source directly inside the barn, then the heating would be too uneven, unless you did something really creative with multiple flues from one stove.

Bob

A diagram of a cheap, efficient, and durable flue is given in Plate I, showing the ground plan of a tobacco barn 20 by 20 feet and the arrangement of the flues therein- Plate II shows the elevation.

To construct flues on the plan given, it is first necessary to cut out two or three logs from the end of the barn; then build the walls of the flues 12 or 13 inches distant from the sills or walls of the barn, as at EEEE, in Plate I, and projecting outside the walls at AA 18 inches. Build the walls of flues 18 inches apart, and 18 to 20 inches in height at the openings AA, decreasing in height as they run back to 14 inches at CC. Put in sheet-iron pipes at CC, 10 or 12 inches in diameter, equidistant from the flues and from each other, and carry them through the body of the barn, out at DD, with the ends elevated at DD 3 feet higher than at CC. The flues should be arched with brick or covered with flat fire-proof stone for about 5 feet from AA to BB; then cover the flues from BB to CO with sheet-iron. Use No. 16 iron nearest the fire, commencing at BB, and thinner iron, No. 18 or 20, for the remainder of the covering.

A cheap flue is constructed by cutting ditches in the floor of the barn from 15 to 18 inches wide and as deep as necessary and covering them with sheet-iron, as recommended for the stone or brick flue. A better one is made of mud walls, covered with sheet-iron. The mud walls are built by placing two wide boards I; from 12 to 14 inches apart and packing moist clay between them, beating it down hard, in position and arrangement similar to the walls of stone, and covering with sheet-iron. Upon firing the flues the boards are burned away and the dirt walls are hardened. If the clay is of proper quality, such as is fit for making tolerably good bricks, these walls will last a long time. It is necessary with the ditch or mud-wall flue to attach furnaces of stone, brick, or iron.

 

[BarG]

Thats an interesting post deluxe, maybe by this time next year we can figure out an economical way to do this on a small scale. I,ll try to do more research into old fashioned ways of flue curing. It doesn't seem to be quite so quick and easy to do it properly the more i'm learning. I would still like for mine to be a temporary structure as it will only be used for a few weeks out of the year, and maybe not every year,depending on if and how well it works. Just for grins what if you bulit a large covered fire pit outside the structure with a covered coming out from ditch running inside through the middle with multiple flues spaced srategicly going from floor to ceiling with those butterfly gates or whatever you call them to control the flow of heated air and smoke. It seems to me the hardest temps to control would be the higher ones, the initial temps might not need any heat at all during the day in this weather with a metal structure. Thanks for the post I'll keep trying to learn more about flue curing and methods.

 

[Daniel]

I am looking at trying to flue cure nearly half of my crop this year. I am growing a total of nearly 1800 plants so will need to be able to flue cure nearly 900 of them.

I have several questions that if I had answers would be helpful in my planning.

First and most obvious would be how large a structure will be needed for this many plants?
Related to the above is how tightly can the plants be packed? I am familiar that tightly packed plants and higher heat causes rot faster.
I have also wondered as I thought this over if piling of the tobacco is just one other method of flue curing.

In the pdf linked to above there is a comment that once the leaf is dried no further change is being made in the leaf. This woudl mean by the simplified method of flue curing. 100 degrees until leaf is yellow then 130 degrees until leaf is dry. The additional stem drying woudl not make a difference and the period of 160 degrees to dry the stem is not really making any difference in the tobacco. If so I could omit the stem drying period completely and only need to worry about maintaining a 130 degree atmosphere until the leaf is dry.

I am looking at a Rocket Mass Heater as the heat source. It is also a good example of a horizontal chimney and how it will deliver it's energy to a structure. In order to heat a curing barn you would not cover the duct work in a mass. The burn box could be located outside the structure with the burn tunnel passing under the wall and the heat riser and duct inside. The duct eventually passes back through a wall to vent. A gas fuel source controlled by a thermostat and you have some failry decent control over temperature. If I am correct you only need to operate this for 3 to 4 days if you do not go through the stem drying portion. and the max temperature becomes 130 rather than 160. As I see it once the leaves are dry they can be removed from the stalks and there is no need for the additional use of fuel. If the stem they refer to is the mid rib they can be air dried without effecting the final product.

Mainly what I am looking for is a temporary structure that I can maintain at 130 degrees for at least a couple of days in late summer. Keep the humidity at acceptable levels which should not be any problem in my location. Then be able to take down and store the parts.

I am also not sure on just what they are talking about by racks or boxes for packing the tobacco in.

Is the tobacco cured whole stalk or are the leaves removed from the stalk to cure it? If it is the leaf only that reduces the space needed by a great deal. Even if the leaf is in hands or stacks or hung individually on racks.

 

[deluxestogie]

Daniel,
I'm certainly not an expert at flue-curing, so I'll just give you my take on it, for what it's worth.

What you are proposing seems to be simply accelerated color curing. You may be able to dry the leaf at your desired color, but without raising its temp above 149ºF, the primary enzymes of the leaf will still be intact, and will continue to age the leaf fairly rapidly (compared to "Bright-cured" leaf), and allow it to darken, and go into a sweat if the conditions permit. If what you are after is "Bright-cured" leaf, which is what commercial flue-cured is, with its stable lemon color and typical cigarette acidity, you'll have to take the temp higher than 149ºF.

The tobacco is often leaf leaf-primed. The original goal of flue-curing (pre-1850s) was to allow it to be safely and quickly stored, without risk of decaying or going into a sweat in the hogshead. So lower temperatures, like those you suggest, were used, though for a longer period, to allow the stem to dry. Without even drying the stems, you'll be setting yourself up for a heap of stemming with every batch.

Once the high-temperature "Bright-cure" was accidentally discovered, the goal became producing lemon-colored tobacco that retained that color. Your plan won't accomplish that, even though you immediately stem the leaf.

Last September, I noticed that the temperature of a closed, galvanized garbage can fairly predictably rise to 100-110ºF in direct sunlight. That's how I initially yellowed my leaf prior to fire-curing, but it required a couple of weeks to yellow. (It was Shirazi, which otherwise tended to dry green. In this case it all fully yellowed.) I had no wet-bulb, so it probably should have had the lid ajar more of the time.

Roanoke Flue-Curing Barn. This one, and 13 more, are for sale, used, for $1200 each (in SC).

Commercially today, flue-curing structures look like semi trailers (e.g. the Roanoke barn), and are designed to hold leaf on sticks much like a traditional barn. You'll need space between the leaves to evenly carry out the flue-curing process. Some modern flue-cure structures have automated chain-driven racks, so you can load all the tobacco while standing at the door, and a computer controller into which you load a program of heat and humidity vs time, and just flip the switch.

So probably hands of leaf would not work so well (poor ventilation). Piling leaf will cause it to go into a sweat (ferment), which flue-curing endeavors to prevent.

I would suspect that you need to run the whole heating/drying routine up to 150ºF+, to end up with the product you have in mind.

Bob

 

[BarG]

Bob, Last year I primed a large batch of leaves of mc and left piled in shade on my porch for quite a few days,I noticed that a lot of the leaves at bottom of pile started yellowing, any longer and I think they would have begun to rot or mildew. The yellowing was much brighter than the leaves already hung to air dry . I guess the question for me is would hard to air cure varietys benefit from this.

edit, outdoor temp was 95-100 degrees in the shade.

 

[BigBonner]

I used a small cooking stove with every burner going even the oven , In a building , I put up plywood sides and left the top open for the moisture to escape . It was hard to adjust the temperature and it took alot of LP gas .
The last batch I did I was out of gas for a while before the company brought more . I had tobacco there to flue cure . It laid in a pile for quite some time . I would flip the tobacco every now and again . The tobacco is still laying on the rack and I never got to flue cure it . The leaves turned a dark red , but the smoking part is really good . I mix some of it in for my own use .
I have some whole stalk cured flue tobacco it is a fairly good smoke . These were a test run .
Out of all the ways to cure flue tobacco its best Heated , but to me pile and whole stalk is just about as good .

I see the price for the Roanoke Flue-Curing Barn is $1200 . I would like to have one but I would say shipping it to me would cost more than the barn cost .

Flue barns also have fans that draws air through the tobacco to bring out the moisture . First primings most usually are lemon colored and the rest are most usually a darker brown to red in color .

One thing to remember about green tobacco is that left piled for a day it will heat up by itself and smell like peaches ,Flue may smell a little different .

If I load a load of tobacco on a wagon when Im harvesting it and leave it on the wagon for a long period of time , it will heat up and smell bad .

We cut burley tobacco and it is placed on a tobacco stick and let it wilt in the sun for two days if possible , its according to the weather , rain , etc .We load tobacco and unload during the day . At late evening just before dark we load all wagons to have for unloading early the next morning . If the tobacco sits on the wagons to about lunch the next day they will be hot and smell like peaches .This leaves the tobacco a color cured green .

 

[johnlee1933]

Thats an interesting post deluxe, maybe by this time next year we can figure out an economical way to do this on a small scale. I,ll try to do more research into old fashioned ways of flue curing. It doesn't seem to be quite so quick and easy to do it properly the more i'm learning. I would still like for mine to be a temporary structure as it will only be used for a few weeks out of the year, and maybe not every year,depending on if and how well it works. Just for grins what if you bulit a large covered fire pit outside the structure with a covered coming out from ditch running inside through the middle with multiple flues spaced srategicly going from floor to ceiling with those butterfly gates or whatever you call them to control the flow of heated air and smoke. It seems to me the hardest temps to control would be the higher ones, the initial temps might not need any heat at all during the day in this weather with a metal structure. Thanks for the post I'll keep trying to learn more about flue curing and methods. Here's a pretty cool video of a wood fired curing barn in operation, ignore the promo at beginning http://www.myfox8.com/videobeta/697...a26e/News/Roy-s-Folks-Wood-Fired-Tobacco-Barn

FYI I tried the URL and got a "Sorry page not found."

John

 

[Daniel]

Bob, Thank you. Your point on the temperature was one concern on my mind. I could not recall what temperature you had mentioned before that the enzyme action was stopped. For this year at least I am looking for the higher sugar content tobacco. What I am really looking for is what produces more of a "Cigarette" tasting tobacco. I chose to try and flue cure when I read a post mentioning how well Larry did with Flue Cured Virginia.

After my previous post I did some searching. There are several places that give everythign from very brief explanations to very details as to flue curing. I found a University report for 2011 like the one in the link above from Georgia. still they did not go into detail as to the facilities involved.
Eventually I came across a reference to "Bulk Curing tobacco" so I searched that. I came across this company.
http://www.bulktobac.com/index.html
searching through the items they manufacture has answered a lot of my questions.

Today it is common for the leaf only (No stalk) to be loaded on racks like these. (Scroll to bottom of page)

This is copied from their page about the box.
[SIZE=-2]The box size is 116" wide x 32" deep x 65" high and has 140 Ft.[SUP]3[/SUP] (4m[SUP]3[/SUP]) of holding capacity and includes 72 pins to hold the tobacco in place[/SIZE]

Reading further it says that as much as 2200 lbs of green leaf can be packed in that box.

Now the question is how many lbs of green leaf can I expect to get from 720 plants?

 

[deluxestogie]

The little snippet of an article that can be viewed here: http://pubs.acs.org/doi/abs/10.1021/ie50506a021, suggests that 82% of the green weight is lost during flue curing. If you low-ball the whole cured leaf weight at 1/4 pound per plant, you end up with an original green weight of ~1.25 pounds of green leaf per plant. If your yield of cured whole leaf is more like 1/2 pounds per plant (which is where mine came out, exclusive of Oriental varieties), then the estimate is ~2.5 pounds of green whole leaf per plant. It seems like 2 pounds of whole green leaf per plant is a good working figure.

Bob

 

[BarG]

FYI I tried the URL and got a "Sorry page not found."

John

They must have removed from their archive, It was an old wood building used to flue cure by a couple of old timers. I'll delete shortcut and try to find again.

pdf for flue barn construction http://repository.lib.ncsu.edu/coll...7/3/0003_Fluecuredtobaccobarnconstruction.pdf

 

[Daniel]

Thanks for that link BarG. It appears to me that building a Flue Curing chamber may not be as easy as say building a kiln. But does not necessarily require building a barn either. I am pretty sure it is going to require some detailed attention to making the air pass through the tobacco rather than around it. ALl I can do for now is make my best guess at teh size of the chamber and also be ready to make it to some degree adjustable. I suppose to large woudl not really hurt as long as you can control the temperature at what is needed.

If Bob's numbers above are reasonably accurate I need room for 1440 to 1750 lbs of green leaf. Given over size allows me to leave more air space between leaves then one box of the dimensions I listed before would hold my entire crop. If the tobacco is primed I could go much smaller than that since each batch of primed leaves would be cured before the next batch is harvested. I am thining of a box that has a fan blowing in from the top to a narrow chamber that allowes the air out through pvc or other pipe. this pipe will be perforated with holes so that the air flow is dispersed throughout the bulk of green leaf. THis or some other method of creating veins that force the air to pass more evenly through the tobacco rather than just create a river of air that flows around the leaves. I saw reference that even a 1/2 inch gap of free space will cause the air to travel around the tobacco rather than through it. care must be taken that the leaf is loaded evenly in the chamber.

 

[deluxestogie]

Here is an interesting concept design that I found on http://tobaccodocuments.org/, while searching BATco (British American Tobacco Company) for the term Latakia. The site broke down while I was trying to go back and get the complete reference.

(Sorry about the tilting. It's what happens when a bunch of lawyers use photocopy machines.)

The device seems to be just a closed circuit forced-air heater. Conceptually, it seems to be the same as the Roanoke Barns. With a suitable fan, I would guess that a discarded electric baseboard heater could do the job.

Bob

 

[Jitterbugdude]

Daniel, I'm not sure what it's going to cost you to build and fuel a Rocket Mass Heater, but you might want to look in your local paper (such as Craigslist) for a used mobile home oil furnace. Around here they typically go for $100.00. Add a 5 gallon pail of heating oil and you are all set to pump out copious amounts of heat.

Randy B

 

[leverhead]

I know this is kind of an old thread...... I've gotten a late start, about 100 Virginias are in the ground and about 70 slow pokes next week. I'm thinking I need to be constructing some kind of system for flue curing by the end of June. Is there anybody further along than I am? I still not certain I can identify the difference between mature, ripe and over ripe leaves, so this ought to be quite an adventure.

 

[Jitterbugdude]

Keep in mind you do not have to flue cure your tobacco. Only do so if you want to.

 

[Daniel]

Leverhead, YOu will get a feel of a ripe leaf as your plants progress. Different varieties show different signs the leaf is ripe. Here are the four thins I look for.

The leaf will start to develop yellow spots. This one is the hardest for me because leaf will start to yellow for several reasons so ripe is not necessarily the reason all leaf turns yellow.

The leaf gets a rough texture to it's surface. May call it the alligator skin and I also think that fits the description.

The leaf will become sticky, You will know what that means when you feel it.

Finally if you grasp the base of the leaf between thumb and finger or fingers and try to bend it downwards against the stalk. A ripe leaf will snap like a stalk of celery where an unripe one will be flexible and bend. If the leaf snaps the issue of ripe is pointless as it is now harvested.

There is also a range of ripe and from everything I have found harvesting sooner is better so don't kick yourself if you harvest a leaf that you didn't think was quite ripe. As you go you will develop a since of judgment.

As for the Flue Curing. It is a process that I have nothing more than idea for at this point. I will not have more than that until my harvest comes in for this year. Basically we kiln leaf after it has been cured. I am simply thinking of how to kiln tobacco while it is still green and bring it to much higher temperatures. So basically I am thinking of a kiln with the addition of a fan to keep air moving. also moisture control will be an issue. green leaf being dried quickly will give off a lot of water. that water will cause mold mildew and just plain rot if it is not removed. So far those are the issue I see for flue curing. I have a large kiln alerady. I am lookign at what it might take to adapt it to a flue curing chamber when I desire that ability. I am thinking it will serve for flue curing as my air cure tobacco is curing. and I will be done with it before that tobacco needs to be kilned. This way I get double duty from one machine and do not have to double the cost or the space needed for two containers.