John Paul’s Cigar Humidity Guide



This is my attempt at a comprehensive, but easy to understand guide to understanding humidity as it pertains to cigars. It is probably more information than most cigar smokers need but it is something that I wish I had when I started storing cigars. Anyone not interested in excess information, this guide may not be for you.



Humidity



Humidity is the amount of water vapor in the air. That is water in a gas state, as opposed to being liquid or ice. There are three common ways at quantifying that humidity; absolute, relative, and specific. Specific humidity is not useful to cigar storage so I will not attempt to explain it.



Relative Humidity

With cigar storage, relative humidity is what is most useful to us. So what is it? The technically correct definition as provided by Wikipedia is “Relative humidity is the ratio of the partial pressure of water vapor in an air-water mixture to the saturated vapor pressure of water at a prescribed temperature.”



If that left you scratching your head I will put it in simpler terms. Only so much water can exist as a gas at a specific temperature and pressure. To simplify things we are going to ignore pressure. One hundred percent relative humidity (RH) is the maximum amount of water vapor in the air possible before it starts to condense back to liquid water. Zero percent RH has no water vapor in the air. Since warm air allows for more water vapor quantity (absolute humidity) than cold air, in a closed system, humidity will go down as temperature goes up and vice versa.



Absolute Humidity

Absolute humidity (AH) is simply how much water vapor is in the air irrespective of temperature or anything else. One might think that it would be more beneficial to keep track of AH so cigars would be kept in constant volume of water vapor vs. RH where the amount of water vapor would change depending on temperature. Some people actually do this. I however, believe that is wrong.



I have read various explanations on why cigars might not care about AH, and have understood some of them. I have also read about experiments various people have done, most of which came to the same conclusion as I did when I experimented with it a couple years ago. Whatever the reason, cigars don’t care about AH.



Temperature

The common logic for cigars storage is to store them at 70º F. Personally I think there is a much wider acceptable range as long as you keep a few things in mind. Tobacco beetles are known to be able to hatch in temperatures in excess of 70º F (some say 65º F.) If you properly freeze your cigars this becomes a non issue. I believe at some temperature the tobacco can kick into some sort of a fermentation stage and become “sick” developing ammonia. What temperature this is I don’t know but my personal experience has shown it being somewhere north of 80º F. As for a lower limit to temperature this is simply limited to being able to maintain humidity. The cooler the air, the slower water evaporates, so the harder it may be to maintain the desired RH.



I think what is much more important to cigar storage is temperature consistency. Small changes in temperature cause big changes to RH. If you can keep your temperature stable, or at least so the changes are gradual, then it makes it much easier for the humidifier to keep the RH stable. A simple demonstration is to put a hygrometer in a clear sealed container and put it in a window. The RH will drop as it heats up during the day and rise again after the sun goes away.



Correct Humidity for Storage

Just about any retailer or magazine is going to say that 70% RH is the proper humidity for cigars. Any cigar message board is going to show recommendations from its members anywhere from 50% - 70% RH. The truth is that it is all personal preference. It is pretty much universally agreed that above 70% RH cigars start tasting bad and usually have poor draw. On the lower end the only thing you really need to be aware of is that the lower the humidity the more brittle and easier to damage a cigar becomes. Many retailers purposely over humidify their cigars to prevent damage in shipping.



Measuring Humidity



Analog Hygrometers

Analog hygrometers are generally either cheap or very expensive. The cheap ones use a piece of salt impregnated paper to measure humidity and are very unreliable and should never be used. The expensive ones use hair (natural or synthetic) and are usually accurate and reliable. The only downside to them really is cost. You have to pay a lot more for a good hair hygrometer than you would for a digital.



Digital Hygrometers

Digital Hygrometers can vary quite a bit but I’m going to generalize the problems inherent with them in general. There are different types of electronic humidity sensors but they all have the problem that the sensor has to be open to the air in order to measure humidity. Because they are open to the air they are susceptible to contamination which can cause drifts in the readings. The physical properties of the sensors themselves have a tendency to slowly drift over time as well. Some digital hygrometers can be sensitive to changes in battery voltage. Button batteries do not have a steady voltage their entire lifespan. Alkaline batteries have a slow voltage drop toward the end of their life and silver and lithium oxide usually have a slightly higher voltage for the first few percent of their use. The point I am trying to make is that all digital hygrometers will drift and they are incapable of staying calibrated over time. This is not a flaw in manufacturing but a limit to the technology.



Hygrometer Calibration

If you want an accurate calibration don’t calibrate at 75% RH. Very few hygrometers can read accurately outside of about 20-80% RH. Many are fairly inaccurate above 70%. What happens when you calibrate near the usable range of the meter is that you are setting your baseline on an unpredictable target. A meter can be off by 3-4% RH at 75% but be dead on from 60-70% RH. If you calibrate that meter it will make it less accurate in the range you are using.



What I do is calibrate at 65% RH with a large Boveda 65% bag in a small clear air tight container. Simply put the Hygrometer and the Boveda in the container for 6-24 hours and then record the reading. I use a small sticker and just write the offset and put it on the front of the meter. It may not be the most attractive but it is the most accurate. Some Hygrometers les you dial in an offset making the sticker unnecessary.



Humidifiers



Fruit Based Humidifiers

Some people put a cut apple in their humidor to add humidity. Seriously, I’m not kidding. It is an old practice that should have been forgotten a long time ago but still crops up occasionally. It is not a practice I recommend.



Propylene Glycol Based Humidifiers

Propylene Glycol (PG) is a food safe (in smaller quantities) compound that is commonly found in many foods and medicines. It has the ability when mixed in a 50% solution with water to regulate close to 70% RH. Other ratios will raise or lower the humidification point. It is most commonly used on humidifiers containing floral foam and is the type that most low cost humidors include. The Floral foam is used to give a large surface area to allow for faster evaporation of water. There are also Gel humidifiers that are PG and water solution in a gel form factor. They work the same way but have a smaller surface area which makes them slower to humidify. Although technically PG solution is a two way humidity regulator (will both absorb are release moisture) its absorption abilities are very poor and it is commonly considered just a humidifier.



The main problem with PG based humidifiers is that the ratio of the PG to water is constantly changing as the water evaporates faster than the PG so the regulation point changes over time. It is also not uncommon for the floral foam to start breaking down over time and mold to grow on it. Their main benefit is that they are very low cost. My personal opinion on these types of devices is that they are not worth messing with.



Active Humidifiers

Active humidifiers are electronic devices that contain a reservoir with either water or PG solution and a fan that turns on when it needs to raise the humidity to its set point. They have the ability to release a lot of humidity very fast and that makes them very well suited to large humidors. They are generally one of the most expense options, but they are also very low maintenance and easy to use. It should be noted that they are not well suited to small and very well sealed environments as they will leak humidity even when the fan is not on, and the fan needs headroom for the air to mix. If the fan is blowing directly on something, that something is going saturate with moisture and eventually grow mold.



Silica Based Humidifiers

The most common Silica based humidifiers are Heartfelt beads and crystal kitty litter (always use unscented litter). Both of these work on the principle of equilibrium. The exact science is kind of hard to understand but basically they are a buffer that wants to be at the same RH as the air. As the humidity in the air raises or falls the silica will absorb or expel water to become in balance. This balance point (RH) is entirely dependant on how much water you put in the silica so you have the ability to choose the RH. Heartfelt is basically the same as the crystal kitty with an added salt treatment that they claim helps maintain a specific set point. My experience is that the salt treatment changes little to nothing.



Silica based humidifiers can work very well and are extremely cost effective especially for use in coolidors and wineadors. It is important to note that they are not really an active regulator at all but only a big buffer. You will have to actively monitor the RH and learn how much water to add to maintain it. Some instructions will tell you to wet the silica until half of it is clear. My experience is that this is almost never true and that is usually too much water.



The only negatives I have found with the silica is that it breaks down and dusts off over time (kitty litter much faster than Heartfelt) and personally I don’t care for the smell of the dust.



HCM beads

HCM (also known as Shilala beads) are a clay based bead that work in the same way as silica. The difference is that the HCM is a small bead that has been fired into a ceramic in such a way as to make thousands of very tiny holes. This gives the HCM bead the ability to hold a lot of water and have an extremely large surface area to evaporate from very fast. Also due to them being ceramic they do not break down and are expected to last forever. They are a bit pricy but for the performance I would consider them reasonable. They also work great in conjunction with an active humidifier or Boveda packs. You should never use them with PG though as it may clog them up and reduce their ability to work correctly.



Boveda

Boveda packs are a salt solution based humidity regulator. They are the most accurate regulator on the consumer market (usually within half a percent). They are at least four times as accurate as most good hygrometers. They consist of a salt/salts, water, xanthan gum, and, depending on the RH level, some have Glycerin and/or Citric acid. This solution is contained inside of a reverse osmosis membrane that only allows pure water to escape. They are so safe to use you can keep them in direct contact with cigars with no ill effect.



So how does it work? It is basically the same thing as the salt test many use to calibrate their hygrometers. A solid salt acts as a desiccant (absorbs moisture). Completely saturated salt water (no undissolved solids) acts as a humidifier. When there is both a solution and solid salts then two way active regulation will occur at a level dictated by the salt/salts used. For example table Salt is Sodium chloride which regulates to 75.4 % RH (at 70º F if you want to get technical, Temperature does shift it a bit). Other salts can be used for other RH points such as Potassium citrate monohydrate that regulates to 62% RH. Unlike PG the regulation point does not change as the ratio of salt to water changes so it stays accurate as long as you have both water and salt in the bag (the salt crystals are large enough you can feel them).



The down side to the Boveda packs is that they are slow to regulate. That means that they are not effective in large or leaky humidors generally. Also any of the smaller bags are useless for cigar storage so you should stick to the large bags. You also have to make sure you are using enough of them to make up for the slow transfer. There is a way to make up for this by combining them with a buffer instead. A Boveda bag in a sealed container with some HCM beads gives perfect humidification with a fast response and no headaches, maintenance or hygrometer.



Although Boveda says their product is non refillable (rechargeable?) this is not true. All you have to do is put them in a sealed container with water (a wet sponge works well) and they will refill on their own over the course of a week or so. You just want to make sure that you do not over fill them. If you cannot feel the salt inside the bag anymore they will not properly regulate until you dry them out a bit. Also if you let the bag get too low before you recharge it the performance may be reduced (regulates slower than when new).



Conclusion

I hope this guide was helpful. If I got something wrong, or there is other information that should be included or expanded on, please let me know so I can update the guide. I will try to keep this post updated so digging threw the thread will not be nessasary.

Last update on March 11, 6:33 pm by John Paul.