Cigar Storage: Temperature-Humidity Psychrometry

[Qrash]

All cigar enthusiasts recognize the importance of properly storing, conditioning and humidifying their precious possessions. However, almost without exception, I see debate only discussing HUMIDITY levels … completely ignoring that hygrometers measure RH (Relative Humidity) and reading threads as people obsess about 65% or 70% or 75% or whatever … but completely ignoring the “R” (Relative) in RH. I have seen several references that report the “ideal” cigar storage / aging condition is 72F at 67%RH … and that closely approximates the conditions of the mantra commonly expressed as 70/70 or 70F at 70%RH.

It is imprudent to discuss hygrometers and humidity levels, devices, beads, foam, absorbent polymers (my preference), propylene glycol, etc., etc., etc. and only mention an RH reading … without recognizing the critical role that TEMPERATURE has on RH. I am including (below) a Psychrometric Chart that displays the relationship between Temperature, Relative Humidity and the weight of water content in humidified air. Just a quick summary of a few data points …

All at Relative Humidity of 70%:
At 60F air contains 55 grains of water per pound of dry air.
At 70F air contains 80 grains of water per pound of dry air.
…. Note: A whopping 45% more water is in 70F versus 60F air at 70%RH
At 80F air contains 110 grains of water per pound of dry air.
… Note: A whopping 38% more water is in 80F versus 70F air at 70%RH
… Note: A whopping 100% more water is in 80F versus 60F air at 70%RH

I am always amazed, entertained and even a little dismayed by discussions about “my humidor has (or my cigars have) this problem or that problem, but dammit, my storage humidity is just fine.” Let’s consider two fictional cigar aficionados with “humidity” questions or complaints. In fact, let’s say Messrs. X and Y even have identical humidors … ABSOLUTELY IDENTICAL including equipment, humidification devices (… for our discussion, 70%RH beads) and cigar contents. The only difference is Mr. X keeps his humidor in a nice, cool basement at a nice, steady 60F temperature. On the other hand, Mr. Y keeps his humidor in a comfortably warm closet at a nice, steady 80F.

Again … Note particularly that BOTH gentlemen are using identical storage apparatus including 70%RH beads … and both gentlemen are puzzled by their “problems” because they are tickled that their hygrometers (that they religiously monitor) read spot-on at 70% RH. All should be good … yes? Sorry … NO!!! The sample data presented above provides the ANSWER.

Cigars from Mr. X’s 70%RH humidor (at 60F) will contain only HALF as much water (moisture) as cigars from Mr. Y’s 70%RH humidor (at 80F) due to the ambient storage temperature differential … and when both select an “identical” cigar, they will have VERY different smoking experiences … with one cigar being way too “dry” and one being way too “wet” when compared to “ideal” storage conditions of 72F at 67%RH (equivalent to 70F at 70%RH).

Okay … just trying to summarize and reinforce: There seems to be persistent discussion and dialog (obsession?) about HUMIDITY without consideration of the EQUALLY important parameter, TEMPERATURE. I’m just urging awareness that any humidification / storage methodology will be problematic unless EQUAL care and attention are applied to keeping BOTH Relative Humidity AND Temperature in a steady (narrow) range (… and probably most importantly …), a range that provides cigars YOU consistently like to smoke … Qrash

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[cmiller]

By Jove your right.

However most of your reasoning is wrong.

Temperature is important but not because of the change in absolute humidity with temperature. Temperature is important because at too high of a temperature tobacco Beatles start to hatch and higher temps would encourage mold growth. Too low temperatures slow down or stop the aging process which we like in our fine cigars.

That said, I'm going to borrow a few salient points from http://www.cigargroup.com/faq/#5.0a which you can go read at your leisure.

Originally Posted by http://www.cigargroup.com/faq/#5.0a

The modern myth of varying humidity with temperature is based on an entirely false premise. Cigars don't care about absolute moisture content. They need just enough moisture to keep the tobacco pliable, but not so much to swell it. This occurs at 70-73% REGARDLESS of temperature.

Tobacco should be kept at a relative humidity which just keeps the leaves pliable without swelling them. Since that pliability is based on the interaction of the cellular membranes with the air surrounding them, *relative humidity*, not absolute moisture content is what's important. This isn't chemistry, it's mechanics - on a cellular level. Ideally, the correct point is 70-73% regardless of temperature. At 70% relative humidity (a measure which by definition is independent of temperature) cigar leaves become pliable without swelling. at 75% or higher, the cells begin to swell. at 68% or lower, they can become brittle. These points are regardless of the ambient temperature or the absolute moisture content.

So basically yes at a higher temperature the air holds more water but what you fail to realize is that at a higher temperature fewer of the water molecules will bind to the tobacco because the kinetic energy is higher.

Originally Posted by http://www.cigargroup.com/faq/#5.0a

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

Edit: Oh, and welcome to the jungle, interesting first post.

Edit 2: Oh, and some folks here prefer 65% RH

[xrundog]

Temp. is important. Unfortunately, unless one lives in a climate controlled house (Gotta love central air) one is at the mercy of the seasons. The hygrometer is all one has to go by.

[quote=Qrash]. I’m just urging awareness that any humidification / storage methodology will be problematic unless EQUAL care and attention are applied to keeping BOTH Relative Humidity AND Temperature in a steady (narrow) range

[quote]

ergo, the reason some of the LLGs use frigdadors, controls temp and humidity within narrow ranges. Coolidors that are left closed for long periods of time and not stored in direct sunlight also tend to control temp and humidity.

I see the reasoning in both yours and in Cmiller's posts. I do know from personal experience that the humidity in my humi tended to flucuate wildly when my humi was close to the A/C vent. Away from the vent (and the cold/warm cycle), it is a lot easier to maintain a consistent RH.

In any event, I tend now to go more on feel as I get more used to my collection. I seem to also be leaning more to 60-65% RH range than the 65-70% range I used to run. Lower RH seems to involk less tunneling in all my cigars (C & NC).

[joed]

So, actually there is a third point that you might consider - especailly if you are interested in what causes mold growth. As a certified mold remediation specialsts-American Indoor Air Quality Council, I have a little experience with mold. The dew point is very important and should also be introduced into your discussion. The RH of the air does not promote or support mold growth, but the surface moisture does. So, 70% RH, if the temp drops below the dew point - results in 100% surface - Moisture + food source - read as any organic material = mold growth. Temperature by itself in not a determining factor when considering mold. By the way mold samples are cultured in a laboratory at 70% which is an ideal temp to support growth.

A situation where the temperature is highly variable - as in the kids case - will cause your RH to move a lot - but - where did the water go?

[plexiprs]

[SIZE=3]Also absent from your theory is a discussion of the other variables, that being the equilibrium moisture content of the tobacco, same for the spanish cedar lining of most humidors, and the opening and closing of the humidor and release of humidified air.[/SIZE]

[SIZE=3]Yes, temperature is the part that makes humidity relative. Warmer air as a greater capacity for water and the reverse is true. Higher temperatures cause cigars problems with pests and molds and should be avoided, lest you wish to deal with those problems. But a humidor is really serving a purpose in maintaining the organic materials, tobacco, in an ideal range for their consumption through smoking. Tobacco in general has a moisture content of 14%-17% and this number is used by international carriers in their handling requirements for commercial tobacco products.[/SIZE]

[SIZE=3]Now in our humidor we have organic water-carrying cigars, that allowed to become too dry will then let essential oils and resins began to evaporate thus impacting in a negative fashion the flavors and smoking experience. The air in the humidor carries water and the amount is determined by the temperature of that air, as saturation point is changed with temp. Also, we have the cedar lining, which if properly condition will contain a given amount of water to be determined by the equilibrium point of the cedar, the volume of the cedar, the temp, and the rate of evaporation from the cedar to the air inside the humidor. Oh, and most people have a credo or other device that serves the purpose of buffering or maintaining the humidity of the humidor.[/SIZE]

[SIZE=3]All these variables are difficult to account for and calculate, especially evaporation, so the simpler approach is one of demonstrated practices resulting in a successful conclusion. Cigars are plants and as such contain significant amount of water. Tobacco is cured, removing some water and beginning a change in the plant matrix and balance of materials. Tobacco is then normally fermented or aged. This complex process again changes cellular distribution of resins, oils and other elements that contribute to overall taste. This process also causes changes and releases unpleasant elements as fermentation progresses.[/SIZE]

[SIZE=3]Now our cigar is made, mostly in a tropical locale and is manufactured according to blend recipe and sizing criteria. Once done, our cigar is in fact a cigar and contains a quantity of water in its organic materials. It is at equilibrium with its tropical environment and expected by the maker to be maintained close to these conditions for optimum enjoyment. Soak it with water and structural issues, burning issues and mold become problems. Dry it to much and flavor is lost, burning is too fast and in the end enjoyment is lost.[/SIZE]

[SIZE=3]70/70 has been arrived at as a simple and achievable storage criteria that most any person wanting to enjoy cigars can achieve. Taking its storage into the highly technical realms is a bit much and really involves so many variables that are expensive and difficult to monitor.[/SIZE]

[SIZE=3]History has shown that 70/70 is adequate, but fluctuations are expected, but extremes are unwanted. Cigar enjoyment isn’t a science, and the over-attention to the science of environmental controls in my opinion only hinders the enjoyment!![/SIZE]

[Dr. Stogie Fresh]

Some very interesting points you make Mr. Qrash. I am interested in hearing more.

I did a review of humidity beads recently on my Rating Blog. One of the things I found was that in at least one real-life situation, a warmer environment actually caused the RH to drop. Granted the two humidors were not the same size, but both had the same kind of beads measured out according to the sizes of the boxes. I postulated that the heat was leaching humidity from the box through conduction, convection, or both. I tested this by conducting a post review update and placing the box in the same part of the house that was cooler. I found that as the temperature decreased, the humidity increased. Hmmm interesting. You can read the review here.

But a humidor is not like the apparatus that produced the data on your psychrometric chart, which I assume is a vastly more controlled environment. A humidor has properties that make it more dynamic. The cedar absorbs and desorbs moisture, the inner and outer box of the humidor are subject to conductive heat exchange and the exterior is subject to both convective and conductive heat exchange. All to say that the humidor is more a living, breathing thing than it is a highly controlled climate chamber. That's because we live in the real world, where humidity and temperature change, sometimes rapidly and we need a device that can absorb some of the changes. I do agree with you that a constant environment is the primary goal in cigar storage.

Anyway, just some ramblings on your very spirited and thought-provoking post. As iron sharpens iron, so one post sharpens another. Keep em coming.

Doc

[plexiprs]

Originally Posted by Dr. Stogie Fresh

Some very interesting points you make Mr. Qrash. I am interested in hearing more.

I did a review of humidity beads recently on my Rating Blog. One of the things I found was that in at least one real-life situation, a warmer environment actually caused the RH to drop. ............
Doc

Doc, you are correct and that is displayed in the chart above. As air heats up its capability to hold water increases.

Example:
A 70 degrees F the saturated vapor density is 18.428 grams per cubic meter. 70% relative humidity at that temp and SVD would mean there is 12.9 grams of water per cubic meter of air.

Raise the temperature to 75 degrees. The SVD goes up to 21.669 and the new relative humidity is 59.53, but there is still the same amount of water in the air of that cubic meter, no other changes being made.

Beads would now take some time to compensate for the change in temperature. A case for using something that maintains temp and RH!!

[Qrash]

Doc:

Enjoyed your humidity beads review and have added your blog to my favs list. And I think plexiprs astutely addressed some of your questions and observations. There is another factor with Artsorb (your humidification beads) that may have played a minor role in some of your observations, and that is called hysteresis. Simply put, the beads are not linear in their adsorption and desorption behaviors across dynamic changes in temperature and relative humidity … although Artsorb is pretty darn good.

And, yes, as you correctly describe, one of the most important functions of our humidors is to act as a temperature and humidity “inertial bank” to buffer changes, particularly sudden changes accruing to openings and closings … and otherwise doing our best to implement as consistent and favorable an ambient environment as practicable … Qrash

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[Qrash]

Fantastic forum … glad I joined … !!! … and here’s a little more food for thought:

My intent was (and is) to keep the discussion fairly simplistic. A key (related) factor not originally discussed in consideration of the KISS principle is (indeed) the EMC (or equilibrium moisture content) of the substrate(s) (cigars for us) … more about that later. Now … to debunk some of the flawed feedback:

Let’s start with the prelude for section 5 of The Cigar Smoker FAQ reference:
“Cigars are naturally hydroscopic products. In common with many organic substances, they dry out in the absence of humidity in the air, or absorb moisture from the ambient air. They establish an equilibrium with the atmospheric humidity which surrounds them.”

Suspicions of incompetence from the get-go: No such (science-applicable) word as “hydroscopic.” The correct terminology is “hygroscopic” … as in “hygrometry” … more familiar to many of us via our “hygrometers.” And yes, cigars are naturally HYGROSCOPIC products … and then the two sentences that followed are absolutely correct. In fact those two accurate sentences contradict most of the balance of the argument(s) … and following those two sentences it was all downhill.

Among the most ludicrous statements are:
“Cigars don't care about absolute moisture content.”
Cigars may not care about absolute moisture content … but cigar manufacturers and cigar smokers sure do. Just think about the absurdity of the declaration. Absolute moisture content (ultimately EMC at equilibrium) fluctuates to every one of an infinite number of points (primarily) driven by the second law of thermodynamics and in conjunction with the parameters on the Psychrometric Chart.
... and …
“Again, cigars should be stored at 70 - 73% relative humidity, regardless of temperature. Period.”
If the premises that “Cigars are naturally HYGROSCOPIC products. In common with many organic substances, they dry out in the absence of humidity in the air, or absorb moisture from the ambient air. They establish an equilibrium with the atmospheric humidity which surrounds them.” are true, and they are, a quick glance at the Psychrometric Chart debunks the “regardless of temperature” declaration. Note particularly the conjunction of the Relative Humidity isohume curves as temperature falls … to the point where very little moisture is supported by air in the gas phase (… no matter what the RH level). At lower temperatures there is less water vapor in the air … driving the ECM (equilibrium moisture content) of the substrate (cigar) down to a level where you ultimately end up with an embrittled, dried out stick (given sufficient time to actually reach equilibrium … and more time is generally required to reach equilibrium conditions at lower temperatures due to kinetics).

Some of the information provided by Dr. Patton does address factors that impact substrate EMC. However, please note Dr. Patton’s expertise is in Physiology, not chemical engineering or even chemistry. He (incorrectly) addresses simplistic terminology taught to anyone who attended Chem 101 classes, and stumbles badly with thermodynamics (the “major player” at conditions under discussion) and, with all due respect, I suspect Dr. Patton wouldn’t know the second law of thermodynamics if it jumped up and … oh well.

While cigar storage and aging parameters can be modeled definitively by fairly simple science, there is no need IMHO, nor was there intent, to complicate matters beyond urging a general understanding of the importance of Temperature-Humidity interrelationships to enhance consistency in our collective enjoyment. Once again, my primary (and simple) intent was to emphasize … “There seems to be persistent discussion and dialog (obsession?) about HUMIDITY without consideration of the EQUALLY important parameter, TEMPERATURE. I’m just urging awareness that any humidification / storage methodology will be problematic unless EQUAL care and attention are applied to keeping BOTH Relative Humidity AND Temperature in a steady (narrow) range (… and probably most importantly …), a range that provides cigars YOU consistently like to smoke” … !!!

Oh … since The Cigar Smoker FAQ reference seems to tout “credentials,” I own two firms: One an international engineering consulting firm and the other a nanotechnology research and product development firm. In the latter I have the privilege of leading a team of renown academicians from Penn State and Cornell … all with doctorates and post-docs in disciplines covering chemical engineering, chemistry, civil engineering, engineering physics, wood science and polymer science. While I may lead the team, I am the comparative “dumbass” holding only B.S.ChE, M.ChE and M.B.A degrees from Cornell University … Qrash

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[SeanGAR]

Interesting discussion, thanks.

So what is important? The absolute moisture content in the cigars? How will that relate to the absolute or relative humidities at different temperatures?

[NCRadioMan]

I have no idea what you have written. (way over this ole boys head). Welcome to CS!



NCRM

[plexiprs]

Originally Posted by SeanGAR

Interesting discussion, thanks.

So what is important? The absolute moisture content in the cigars? How will that relate to the absolute or relative humidities at different temperatures?

Yes! Bingo! That is it!

Cigars must contain water, and at a minimum 14-17% of water. Keeps them from losing oils and resins and from burning like cigerette tobacco (flash!).

RH of the AIR is the most variable condition in a humidor. Air changes water content much quicker then the cigars or cedar do, or can. Open the lid, whoosh! Wet air replaced by dry air and now the credo/beads must make up for it.

Why? Cause when the air gets dry enough (below 60%RH) the air will draw water from the cigars (and the cedar).

Less air is better. Big walk-ins are a biatch to keep the RH stabile cause the door opens and closes all day and the HUGE amount of air to try to keep at a set RH.

Fill a container FULL of properly moist cigars. Seal it air tight. Store below 70 deg to keep pests at bay and they will last almost forever! Put them in a perimiable wooden box, that some guy/gal opens every 30 minutes to sniff and drool over, and you must now concern yourself with maintaining the environment.

Temperature changes the EMC and evaporation conditions. Steady reasonable temp and RH = good smokeable tasty treats.

Knew I should have studied harder in chemistry! Interesting discussion, at least the 50% or so that I am able to keep up with. I don't know all the dynamics involved, but I do know from a practical standpoint that when I keep temp close to constant, I don't get near the RH bounce I do when temp is bouncing all over the place. Just a common man's observation.

Now, on with the class. I'm enjoying the discussion, really, I am. Not understanding doesn't equate to not enjoying!!

Kid

[plexiprs]

Kid, you grasped the important part. Since RH is temperature dependant, keeping temperature constant HELPS maintain a steady storage state.

If you have the humi's and sticks try an experiment I did years ago. Two identical humi's, in internal capacity at least. Say two 100 capacity humi's. Season both if needed.

In #1 put 25 cigars, hygro and credo/humidifier/beads. 70% or your choice.

In #2 fill it to capacity with cigars, hygro, credo, etc. Same humidity as #1.

Make sure the cigars ALL came from the same storage conditions. Put both humi's in same location and monitor humidity by opening each once in the morning and once in the evening for a 5 minute viewing.

I found that humidity was so much more consistent in #2. Why? Because the water in cigars move out in AIR very very slowly. With #2 full, the mositure was all in the cigars, not in the air.

Ties back to having a HUGE cabinet humi that requires one heck of a humidification system. Peaks and valleys, don't chase perfection things will equalize, just watch for drastic changes.