If you’ve begun collecting cigars, you’ve probably heard of the 70-70 rule. If you haven’t, it says cigars should be stored at 70 degrees Fahrenheit and 70 percent relative humidity. This is one of the most important rules in cigar storage, but not enough people understand the science behind it.
What is Relative Humidity?
Relative humidity is the ratio between the amount of water actually in the air (actual vapor density) and the amount of water the air can hold before it condenses into dew (saturation vapor density). The formula is below.
If the actual vapordensity was 10g/m3, for example, and the saturation vapor density was 20g/m3, then the relative humidity level would be 50 percent. When relative humidity is 100 percent, the water vapor becomes dew.
How Does Temperature Affect Relative Humidity?
As air heats up, it expands. The added energy forces air molecules farther apart. This means that as air temperature increases, saturation density increases and relative humidity decreases. The water vapor gets spread out over a greater area and has to fill more volume in order to condense into liquid water. As air temperature decreases, the opposite occurs, saturation density decreases and relative humidity increases. The air molecules get closer together, so the water vapor gets compressed into a smaller space and it has to fill less volume in order for it to condense into liquid water.
How Do Humidity and Temperature Affect Cigars?
Cigars exchange moisture with the air, like living, breathing things. As humidity drops, they lose moisture. As humidity rises, they gain moisture. At 70 percent relative humidity, cigars won’t gain or lose moisture. They’re in equilibrium. In a cigar cooler, this occurs at about 70 degrees, which is why cigar aficionados emphasis the 70-70 rule so strongly.
Are There Any Exceptions to the 70-70 Rule?
In most circumstances, following the 70-70 rule will preserve your cigars just fine. However, even the best cigar humidors are not impervious to outside temperatures. If they’re stored in a particularly hot room, they may begin to absorb heat from the surrounding air. If they’re stored in a particularly cold room, they may lose heat to the surrounding air. This is why placing your cigar cooler in a stable environment is so important, but, depending on where you live, not always be possible. Some parts of the country experience large temperature fluctuations during the year, which may make it impossible to maintain a steady 70 degree temperature in your humidor, regardless of how well it’s stored.
If you live in an area where it gets very hot in summer and very cold in winter, check the humidity levels in your cigar humidor regularly. If it is set to 70 degrees and the humidity level starts dropping, it’s gaining heat from the environment. You’ll either want to add more water to the humidor or decrease the temperature until the humidity level rises to 70 percent again. If it is set to 70 degrees and humidity starts rising, it’s losing heat to the environment. In that case, you’ll want to either remove water from the humidor or increase the temperature until the humidity level drops down to 70 percent.
Why are Humidity and Temperature So Important for Cigars?
Cigars contain a small amount of moisture when they leave the factory, normally 12-15 percent and cigar companies work hard to maintain that same level of moisture right up to when you buy the cigar and take it home. That’s because cigars with 12-15 percent internal humidity provide the best smoke. They won’t burn too hot or too cold and allow you taste and enjoy the interplay between the oils, sugars, resins, and tobaccos in the cigar. Click this link if you’re interested in learning more about how moisture levels affect the quality of your cigar.