Temperature versus relative humidity issue.

[Sigarz]

So I did a little wandering around "the google" and came across this nice little excerpt that really helped me understand that what humidity is good at various temperatures. I keep my humis at about 60F and have been wondering more and more lately if the 76-ish RH is where its supposed to be or not. well read this from Dr. David Patton, at the Department of Physiology, UCLA School of Medicine.

"There has been extensive discussion on A.S.C. concerning the effects of temperature on humidity and its application to proper cigar storage. Much of the confusion concerning these concepts comes from not understanding what is happening at the molecular level. My goal is to explain some of the revalent concepts and then to put the concepts together in such a way as to give an intuitive understanding of how they relate to cigar storage.

Cigars are made from tobacco leaves. Tobacco leaves (like most plant material) consist primarily of carbohydrates and proteins. Protein and carbohydrate molecules contain many binding sites for water molecules. A certain proportion of the water binding sites need to be occupied by water molecules in order for the tobacco leaves to be adequately pliable, to burn properly and to age properly. So when we think about humidity as it relates to cigar storage, the most revalent factor to consider is: are the correct proportion of water binding sites occupied? Water molecules bind to other molecules via hydrogen bonds. Van der Waals interactions also participate. This applies to water bound to protein and carbohydrate molecules (e.g. tobacco leaves) or to other water molecules (e.g. liquid water). For the purposes of this discussion, water bound to tobacco leaves will be treated like liquid water.

Temperature is the main factor determining whether a water molecule will be more likely to be in either the gas or liquid (or bound) phases. This is because at higher temperatures, water molecules (like any other molecule) will have more kinetic energy. The more kinetic energy a molecule has, the higher its probability of being in the gas phase. This is because it will have sufficient kinetic energy to break out of the hydrogen bonds and Van der Waals interactions that would otherwise keep it bound. At lower temperatures molecules have less kinetic energy so when they collide with a carbohydrate molecule, for example, its kinetic energy is insuficient to break away from it. The important point here is that at higher temperatures, a water molecule is more likely to be in the gas phase and less likely to be bound. At lower temperatures a water molecule is more likely to be bound and less likely to be in the gas phase.

Another point that needs to be explained here is the concept of relative humidity. Simply stated, relative humidity is the ratio of the concentration of water in the gas phase divided by the maximal concentration of water the air can hold (the saturating concentration) at a given temperature. Air holds more water at higher temperatures. Therefore, if you hold the relative humidity constant and increase the temperature, the concentration of water molecules in the gas phase will increase. If you think about this superficially you may think that because the concentration of water molecules increases in the gas phase as you increase the temperature (holding relative humidity constant)that your cigars will become over-humidified. This is WRONG. Remember, as you increase the temperature, the water molecules are less likely to be bound to the tobacco and more likely to be in the gas phase. Thus, to keep the same proportion of water binding sites in the tobacco occupied by water molecules, the concentration of water molecules in the gas phase must be increased when temperature is increased.

Again, cigars should be stored at 70 - 73% relative humidity, regardless of temperature. Period.”


So that set my mind at ease! here I was all set to write a little computer program to calculate "safe" ranges at various temperatures to equate to the 70/70 goal and this bit of information makes that no longer necessary.

I'm guessing there's been posts about this topic in the past but I thought a refresher might be in order.

[yzingerr]

It is food for thought as I too have been wondering what RH level my humi needs to be at. The general consensus on puff says 60-65%. Im even more confused after reading that (though I do understand what he is saying). Thanks for postin' that info!

[Cigary]

I have 70% beads and it works like a charm and when I know what cigars I am going to smoke I drybox them for 2-3 days which makes them burn straight. This works for me for the last few years and if it ain't broken I don't plan on trying to fix it.

[Delsana]

Not necessarily on topic however...

I mainly am in Arizona, and I really enjoy that place as well, however there is rarely any humidity (which is great for me) and a lot of heat (which is also great for me) and I'm curious if anyone had any tips or advice for humidification or such things for a more enjoyable experience when I'm over there.

Thanks in advance.

[e-man]

Originally Posted by yzingerr

It is food for thought as I too have been wondering what RH level my humi needs to be at. The general consensus on puff says 60-65%. Im even more confused after reading that (though I do understand what he is saying). Thanks for postin' that info!

Note that NOBODY ever states the temperature when they list their rH. Just more proof that it really doesn't matter that much. Just keep them from drying up or getting moldy.


My humidor fluctuates between 70% in the summer to 62% in the in the winter. My basement keeps a nice 65 degrees year round. I don't notice any difference between in the way they smoke between summer and winter. My "go to" smokes always taste great and burn straight.


People make a big deal over nothing. So long as you keep them in a relatively consistent environment they will smoke just fine. My buddy and I can smoke the same stick from the same humidor and he'll always have burn issues and mine will be straight.

90% of the time, it's not the humidity....It's the user.

[yzingerr]

Originally Posted by e-man

Note that NOBODY ever states the temperature when they list their rH. Just more proof that it really doesn't matter that much. Just keep them from drying up or getting moldy.

My humidor fluctuates between 70% in the summer to 62% in the in the winter. My basement keeps a nice 65 degrees year round. I don't notice any difference between in the way they smoke between summer and winter. My "go to" smokes always taste great and burn straight.

People make a big deal over nothing. So long as you keep them in a relatively consistent environment they will smoke just fine. My buddy and I can smoke the same stick from the same humidor and he'll always have burn issues and mine will be straight.

90% of the time, it's not the humidity....It's the user.

I'm Trying to digest your post cause I am anal and worried about mold.
I live in Northern CA where it is always 70°F.
I figured the lower the humidity in my humi (65%) is safe enough, but most humidifiers keep at around 70-72%.
Im not worried so much about the proper humidity as I am about having dry or moldy sticks.

[AlohaStyle]

Originally Posted by yzingerr

I'm Trying to digest your post cause I am anal and worried about mold.
I live in Northern CA where it is always 70°F.
I figured the lower the humidity in my humi (65%) is safe enough, but most humidifiers keep at around 70-72%.
Im not worried so much about the proper humidity as I am about having dry or moldy sticks.

You are just fine. A lot of people I've found prefer around 65% than 70% anyway. It is much better to be around 65% than 72%.

[e-man]

Originally Posted by yzingerr

I'm Trying to digest your post cause I am anal and worried about mold.
I live in Northern CA where it is always 70°F.
I figured the lower the humidity in my humi (65%) is safe enough, but most humidifiers keep at around 70-72%.
Im not worried so much about the proper humidity as I am about having dry or moldy sticks.

Keep your humidity below 80% and you will never need to worry about mold.

Keep your temp below 80 Degrees and you will never need to worry about beetles.

70% at 70 degrees is the common accepted "standard" for cigar storage. You may prefer something different. It may depend on your climate, your preferred cigars, how you cut the head, or personal smoking style.


The thing you need to take from this discussion is:

1) rH is NOT an absolute measurement like temperature. It is RELATIVE, hence the name.

2) Warm air can hold more water than cold air.

3) Relative Humidity measures how close you are to reaching the maximum amount of moisture for air at a specific temperature. The value changes as temperature changes.


Let's assume you are at a "perfect" 70/70, but for whatever reason, your temp drops 10 degrees. 60 degree air holds less moisture than 70 degree air. That means that your rH goes up, even though the total water content hasn't changed at all.

In other words, the rH value is NOT an indicator of the total moisture content of your cigar, unless you maintain a constant temperature.

Let's say you put some cigars in a plastic bag and freeze them. As the temps drops, your rH rises. As your rH approaches 100%, the water cannot stay suspended in the air anymore and starts to condensate and freeze as ice crystals. You can see how cold air hold less moisture than warn air. You can also see that the cigar still has most of it's moisture frozen inside of it, regardless of the rH value of the air.


So, we know that 65% at 75 degrees has more water content than 65% at 60 degrees. So, to say I prefer mine at 65% is a worthless statement if they do not include the temp. They could live in a desert or the arctic, which would make a huge difference. Maybe they live in the same area, but keep their homes at different temps.

65% at 70 degrees might be the same as 70% at 60 degrees (I don't know the calculations). So, one person may say they prefer 70% and another prefers 65%, but both may very well have the same water content based upon their ambient temperature.

To the point of the original post. If your temp is 60 degrees, then you need to maintain a higher rH to have the SAME WATER CONTENT as a cigar at 70/70. Period!!!


People get too caught up in the number, even though they use cheap/inaccurate devices to measure it. The important thing is to get your cigar to equalize somewhere in the ballpark, so you don't have a dry outer and a moist inner (or vice versa). Give them time to rest and equalize with their neighbors.

rH will shift with temperature and the seasons. Accept it. Don't worry yourself over nothing. It takes time to change the moisture content of a large mass of cigars. The rH of the air in your humidor can change overnight, but that doesn't mean that the moisture content of your cigars has changed that fast.


Now, to MY point. I keep my humidor in my basement with a year round 65 degree temp. I see a 6-8 point shift between summer and winter (62-70%) but they smoke just fine all year round. My favorite cigars smoke and taste the same year round. So long as they are in a suitable RANGE, you should be very happy smoking them. Now, my cooler is airtight, so it maintains 70% at 65 degrees year round. Something to consider if you're really anal.

With an rH of 80% and higher, mold spores can extract moisture in the air and start growing. Also, at that humidity, a slight temp change can cause condensation to collect and pool. So always keep your rH below 80% regardless of temperature.

If your rH gets too low, then oils will evaporate from your cigars and you will lose flavor (just as dried spices do not taste as good as fresh spices). Exactly what point that occurs is open for debate. It probably depends upon many factors. However, 60% (at "room temperature") is not a problem based upon experiences of members who prefer to smoke them in this range.

So, since your temp is a constant 70 degrees, you have a better benchmark than most people. Try to maintain a 70% rH for a couple months and see what you think. If you want an easier draw, then try 65% for a couple months and see if you like it better.

Relax and enjoy them

[InvokeMe]

Thank you for posting this information. Fascinating and enlightening.

[yzingerr]

Originally Posted by e-man

Keep your humidity below 80% and you will never need to worry about mold.

Keep your temp below 80 Degrees and you will never need to worry about beetles.

70% at 70 degrees is the common accepted "standard" for cigar storage. You may prefer something different. It may depend on your climate, your preferred cigars, how you cut the head, or personal smoking style.


The thing you need to take from this discussion is:

1) rH is NOT an absolute measurement like temperature. It is RELATIVE, hence the name.

2) Warm air can hold more water than cold air.

3) Relative Humidity measures how close you are to reaching the maximum amount of moisture for air at a specific temperature. The value changes as temperature changes.


Let's assume you are at a "perfect" 70/70, but for whatever reason, your temp drops 10 degrees. 60 degree air holds less moisture than 70 degree air. That means that your rH goes up, even though the total water content hasn't changed at all.

In other words, the rH value is NOT an indicator of the total moisture content of your cigar, unless you maintain a constant temperature.

Let's say you put some cigars in a plastic bag and freeze them. As the temps drops, your rH rises. As your rH approaches 100%, the water cannot stay suspended in the air anymore and starts to condensate and freeze as ice crystals. You can see how cold air hold less moisture than warn air. You can also see that the cigar still has most of it's moisture frozen inside of it, regardless of the rH value of the air.


So, we know that 65% at 75 degrees has more water content than 65% at 60 degrees. So, to say I prefer mine at 65% is a worthless statement if they do not include the temp. They could live in a desert or the arctic, which would make a huge difference. Maybe they live in the same area, but keep their homes at different temps.

65% at 70 degrees might be the same as 70% at 60 degrees (I don't know the calculations). So, one person may say they prefer 70% and another prefers 65%, but both may very well have the same water content based upon their ambient temperature.

To the point of the original post. If your temp is 60 degrees, then you need to maintain a higher rH to have the SAME WATER CONTENT as a cigar at 70/70. Period!!!


People get too caught up in the number, even though they use cheap/inaccurate devices to measure it. The important thing is to get your cigar to equalize somewhere in the ballpark, so you don't have a dry outer and a moist inner (or vice versa). Give them time to rest and equalize with their neighbors.

rH will shift with temperature and the seasons. Accept it. Don't worry yourself over nothing. It takes time to change the moisture content of a large mass of cigars. The rH of the air in your humidor can change overnight, but that doesn't mean that the moisture content of your cigars has changed that fast.


Now, to MY point. I keep my humidor in my basement with a year round 65 degree temp. I see a 6-8 point shift between summer and winter (62-70%) but they smoke just fine all year round. My favorite cigars smoke and taste the same year round. So long as they are in a suitable RANGE, you should be very happy smoking them. Now, my cooler is airtight, so it maintains 70% at 65 degrees year round. Something to consider if you're really anal.

With an rH of 80% and higher, mold spores can extract moisture in the air and start growing. Also, at that humidity, a slight temp change can cause condensation to collect and pool. So always keep your rH below 80% regardless of temperature.

If your rH gets too low, then oils will evaporate from your cigars and you will lose flavor (just as dried spices do not taste as good as fresh spices). Exactly what point that occurs is open for debate. It probably depends upon many factors. However, 60% (at "room temperature") is not a problem based upon experiences of members who prefer to smoke them in this range.

So, since your temp is a constant 70 degrees, you have a better benchmark than most people. Try to maintain a 70% rH for a couple months and see what you think. If you want an easier draw, then try 65% for a couple months and see if you like it better.

Relax and enjoy them

THANKS for the info. I am very well versed in Absolute and Relative humidity, but I wasnt so well versed in actual application of humidity vs. cigars.
Your post was about the biggest help I could ask for from here.
Thanks a bunch!

[bartolomeo]

my goal is 62-65RH and a temp of 65-67

Bart

[MiLKMD]

I have read this and other threads with great interest. However I must respectfully disagree with some of your points, sir. Please also note that I am drawing my conclusions from the quoted ASC article from the UCLA professor. He may be completely erroneous.

Originally Posted by e-man

3) Relative Humidity measures how close you are to reaching the maximum amount of moisture for air at a specific temperature. The value changes as temperature changes.

RH measures not how close one is to reaching the maximum amount water for air but rather vapor pressure of water compared to completely saturated air. RH will change if the absolute water content is held fixed in a given volume. I will concede the point that the absolute humidity required to achieve a given RH will change at varying temperatures, but RH is a ratio: both the numerator and denominator will change equally at a given RH as temperature changes. 70% RH means that the vapor pressure of water is 70% of maximum, therefore 70% RH at 50 degrees Farenheit means that the atmosphere is 70% saturated with water at 50 degrees and 70% RH at 80 degrees is 70% saturated at 80 degrees. Granted the amount of water needed to achieve this is different but the RH is the same.

Originally Posted by e-man

In other words, the rH value is NOT an indicator of the total moisture content of your cigar, unless you maintain a constant temperature.

This is where things get tricky. According to the quoted article from ASC RH does indicate total moisture of the cigar, albeit indirectly. Based on the article, cigars have an inherent equilibrium moisture content (ECM) which is dependent on RH not AH. I will concede the point that the ECM of a cigar may be temperature dependent (would someone please enlighten me) but I presume that it is very small. The often quoted number is that cigars should have 12-14% by weight moisture content. This ratio can be achieved by keeping RH at 70% which is irrespective of ambient temperature. As derived from the article, achieving the correct moisture content in cigars is dependent of a percentage of binding sites filled with water molecules. This percentage is a function of RH not of AH.
Think if you will of RH as the amount of push (pressure) the water vapor has into the cigar. The force of the push is dependent on relative humidity, not on absolute humidity and the water content of the cigar is dependent on the amount of push (RH) and not on how much water the cigar sees (AH). Which is why those tables with changing RH based on temperature are erroneous. If one puts a perfectly hydrated cigar (12% water by weight) from a 70/70 humidor into a warmer humidor with a lower RH as suggested, the cigar will release water to equilibriate with the new environment and will therefore have less than ideal water by weight if kept at a higher temperature but lower RH. Yes the warmer humidor may have equal or more water in the air by weight, but the cigar will release water to equalize with the lower RH.

Originally Posted by e-man

So, we know that 65% at 75 degrees has more water content than 65% at 60 degrees. So, to say I prefer mine at 65% is a worthless statement if they do not include the temp. They could live in a desert or the arctic, which would make a huge difference. Maybe they live in the same area, but keep their homes at different temps.

Again unless the ECM of cigars is extremely variable at different temperatures stating that one likes her cigars equlibrated at 65% RH is an adequate description because it indirectly tells us what percent by weight she prefers her cigars due to equilirbrium at a specific RH. To say that she likes her cigars at 70% RH means that she likes her cigars with 14% water. Her cigars will always have 14% water at 70% RH regardless at which temperature she stores them. Temperature has nothing to do with how much water her cigars hold.

Originally Posted by e-man

65% at 70 degrees might be the same as 70% at 60 degrees (I don't know the calculations). So, one person may say they prefer 70% and another prefers 65%, but both may very well have the same water content based upon their ambient temperature.

To the point of the original post. If your temp is 60 degrees, then you need to maintain a higher rH to have the SAME WATER CONTENT as a cigar at 70/70. Period!!!

I respectfully disagree. You will not have the same water content in the cigar as per the OP. You may have the same water content by mass in the air surrounding the cigar but the cigars will definitely have very different ratios of water content.
RH is the partial pressure of water at a given environment relative to a saturated environment. The pressure of the water vapor is what determines the water content of cigar not the absolute mass of water vapor in the air. Yes at high temperatures air can hold (or more correctly stated transport) more water but if the RH is very low, there is very little water pressure and therefore very little water content in a cigar.
Try this thought experiment. Let's say one has a small humidor at 70% RH with a cigar in it. That cigar has just the right amount of water. If you move that whole box into a much larger humidor and open the small box the RH would drop (same mass of water vapor in a much larger volume) and the cigar would release it's water to fill the new volume. The AH (amount of water in the air) is exactly the same but the amount of water that the air can hold is much larger. That is analogous to increasing temp: increasing temp increases the amount of water that warm air can hold, so you need to have a larger amount water in the air to keep the cigar from drying out. The RH vs temp table is advises you to keep the same amount of water in the air but changing the amount of water that the air can hold...wrong!


I welcome your comments and criticisms.

Originally Posted by e-man

Relax and enjoy them

This FTW.

[e-man]

Originally Posted by MiLKMD

I have read this and other threads with great interest. However I must respectfully disagree with some of your points, sir. Please also note that I am drawing my conclusions from the quoted ASC article from the UCLA professor. He may be completely erroneous.

I welcome your comments and criticisms.

.

I have been reading up, trying to fully understand what you have said, but I must admit that I cannot respond intelligently to your comments at this time. Maybe you can enlighten me.


Here is a chart that I found from a recent post. If this is one of those "Erroneous" charts, then could you please explain the conceptual breakdown or why it is misleading? The full document can be found at the following link:

Cigar Storage/Humidity Requirement


Temp-----Water Vapor Pressure----Relative Humidity Required
------------for 100% saturated-----to equal 70% RH at 70 degrees (13.15mmHg)

60----------13.26-------------------99.17%
61---------- 13.73-------------------95.78%
62---------- 14.23-------------------92.41%
63 ----------14.74-------------------89.21%
64---------- 15.27-------------------86.12%
65---------- 15.81-------------------83.18%
66---------- 16.37-------------------80.33%
67---------- 16.95-------------------77.58%
68---------- 17.55-------------------74.93%
69---------- 18.17-------------------72.37%
70---------- 18.79-------------------70.00%
71---------- 19.45-------------------67.61%
72 ---------- 20.11-------------------65.39%
73---------- 20.81-------------------63.19%
74---------- 21.51-------------------61.13%
75---------- 22.25-------------------59.10%
76---------- 23.00-------------------57.17%
77---------- 23.78-------------------55.30%
78---------- 24.59-------------------53.48%
79---------- 25.40-------------------51.77%
80---------- 26.67-------------------49.31%

I apologize. The chart didn't render preperly, since this site won't display multiple spaces. I replaced them with hyphens so the table would line up.

This chart claims that the Vapor Pressure changes with temperature as would be expected for a relative measurement. It also suggests that you would need to hold 83% humidity at 65 degrees to have the same moisture content as 70/70. The author also claims that you cannot keep cigars below below 60 degrees, as you would need more than 100% saturation to equal the moisture content of 70/70.

How does this fit into your statement that the total moisture in the cigars is not affected by temp, so long as the rH is constant? Could you expand on your example of moving a cigar to a lower RH at a higher temp?

Also, what is the relationship and effect, if any, between Vapor Pressure and Atmospheric Pressure?

[MiLKMD]

Thank you for reformatting the table. I understood the gist from your explanation and reading from the link.

From the link:

Relative humidity is an easily measured value, that relates the measured humidity to the maximum humidity that is possible at that temperature. Thus, 70% RH at 70 degrees F is not the same as 70% RH at 80 degrees F and neither is the same as 70% RH at 60 degrees F.

This is a false statement because it is incomplete. RH is a ratio: the numerator being the actual amount of water in a given volume and the denominator being the maximum amount of water in a given volume before condensation i.e., saturation. So 70% RH at 60 degrees means that the air is 70% saturated; 70% RH at 70 degrees means that the air is 70% saturated and 70% RH at 80 degrees means that the air is 70% saturated. The absolute amount of water in the air (AH) at the different temperatures for the same volume is different, but the maximum amount of water that the air can hold also changes and the ratio stays the same for equal RH values.
Think of a small glass that's half full. It's at 50% capacity. Take a large glass that's also half full. The larger glass is also at 50% capacity. Both are at 50%. Granted the first glass holds much less water, but both are at the same ratio which is analogous to RH.

From the link:

Remember, we are aiming to maintain the same amount of water (mgm/liter) around our cigars as seen at 70% RH at 70 degrees F (which is 13.15 mmHg water vapor pressure).

This is what I believe to be erroneous. We do not want to maintain the same amount of water around our cigars. We want to maintain the same ratio of water to saturation around our cigars.

Cigars are hygroscopic. And as quoted from the article posted by the OP:

Cigars are made from tobacco leaves. Tobacco leaves (like most plant material) consist primarily of carbohydrates and proteins. Protein and carbohydrate molecules contain many binding sites for water molecules. A certain proportion of the water binding sites need to be occupied by water molecules in order for the tobacco leaves to be adequately pliable, to burn properly and to age properly. So when we think about humidity as it relates to cigar storage, the most revalent factor to consider is: are the correct proportion of water binding sites occupied?

As the temperature increases, the kinetic energy of the water molecules in the cigar increases and they will want to break their chemical bonds (hydrogen and van der Waal forces) and evaporate off of the cigar. We want to keep a certain proportion of binding sites filled with water to keep the leaves supple and soft.
To continue the analogy: we have two glasses of water that are both half full. We want to keep them half full the same way we want to keep our cigars at 12-14% water by weight. Over-hydrate the cigars and they will burn awfully and harshly and under-hydrate them and they will burn hotly and quickly.
Now we take the two glasses and put them into separate humidors. The RH in the humidors is 100%, that is the air is completely saturated so the water level in each glass does not change. (I know, I know, evaporation and condensation are in dynamic equilibrium.) In the first humidor we put in a humidification device that always maintains 100% RH. In the second humidor we put nothing.
Then we raise the temperature of both humidors. What happens in the first humidor? The humidification device works to maintain an RH of 100%. No water evaporates from the glass; it is still half full and at perfect hydration. What happens in the second humidor? The RH drops because the warmer air can hold more water (the denominator of RH ratio increases because the saturation point increases). The water in the glass starts to evaporate to bring the RH back to 100% and the water level drops. We have a less than half full glass and a dried out cigar!
The inverse is also true. If we decrease the temperature in the humidors the RH becomes greater than 100% because the saturation point decreases for colder air. Cold air cannot hold as much moisture so water must condense out. We use beads in our first humidor so as water condenses the beads absorb the excess water and our RH returns to 100% and the glass stays half full. In the second humidor water condenses as the RH returns to 100% and without anything to absorb the extra water the water level in the second glass rises; we have a wet cigar!
The table advises us incorrectly to change the RH based on temperature. We do not want to decrease RH in warmer air: that would make our cigars too dry. Similarly we do not want to increase RH in colder air: that would make our cigars too wet. Maintaining cigars at 70% RH keeps the cigars at 12-14% water by weight regardless of temperature and one should not vary RH versus temperature.

The table states that it is impossible to keep a cigar adequately hydrated below 60 degrees because one would need to exceed 100% RH.
Should one be able to sacrifice a few sticks or dog rockets, try the following:
Keep one cigar at 50 degrees Farenheit at 70% RH. Keep another at 60 degrees at 99% RH. I predict that the first cigar will not be dried out and will smoke just fine while the second will be soggy as a sponge and be a terrible smoke. Similarly keep one cigar at 90 degrees at 70% RH and another at 80 degrees at 50% RH as the table suggests. Beetles aside the first cigar will be just fine (and age faster) while the second will be dry as a bone.

In regards to vapor pressure and it's relationship to atmospheric pressure, atmospheric pressure has no relationship on water vapor pressure. Although we say that warm air "holds" more water it is more correct to say that warm air "transports" more water. Air does not have any thermodynamic effect on water vapor and water is not "soluble" in air. Both water vapor and air can be approximated to behave as independent ideal gasses.

I realize in my previous post I used the word pressure to describe the effect of RH. The above is a misnomer and I should not have used the word pressure since we are discussing the partial pressures of water vapor i.e., concentration of water vapor or AH.

And finally the caveat regarding the equilibrium moisture content (which I incorrectly abbreviated ECM. It should be EMC.) I am assuming that EMC of cigars does not change with temperature or changes very little. My assumption is based on the quoted ASC article and from other sources about EMC of organic materials. EMC is the amount of moisture a given substance has at equilibrium given a RH and temperature and for wood it is much more dependent on RH than it is on temperature.

I cannot post links yet but please see Table 1 at owic.oregonstate.edu/pubs/emc.pdf
The EMC table is for wood but we can substitute cigars for wood as an organic material. The EMC or water content of a cigar at 70/70 is 13%. Right in the sweet spot for what we said we wanted for our cigars. If you vary the temp by 20 degrees up or down, the water content of the cigars changes very little if you hold the RH at 70% (it is still within 12-14%). However if you change RH, the water content of the cigar changes drastically. According to the RH vs temp cigar table we are advised to store our cigars in 60 degree weather at 99% RH which would mean that our cigars would absorb water until equilibrium was reached at 24% water by weight. That's a soggy cigar!

I welcome the discussion.

[Cletus]

.
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All this science talk is making my head hurt.....