Why Do Cigars Develop Mould in Your Humidor?

Maintaining your humidor in perfect condition is simple but requires attention to ensure everything is in order. Otherwise, issues like mould can arise. Mould on cigars stored in your humidor is primarily due to excess humidity.

Therefore, achieving the optimal environment inside the humidor is essential to preserve the quality of the cigars and avoid mold growth or other issues. Here are some key points to help you manage your humidor and prevent problems such as mould.

Mould on cigars

Mould are microscopic organisms that live on animal or plant matter. Mould grows and multiplies under the right conditions, which include high humidity (very high humidity, condensation, or direct water) and organic matter (in this case, tobacco). Cedar, the wood used inside humidors, can also develop mould as it is organic matter.

Relative Humidity in the Humidor: The Key Measure

The first thing to understand is that the humidity considered for preserving cigars is relative humidity. This is the ratio between the actual amount of water vapor and the maximum amount of water vapor that the air can hold at a given temperature. Its value is expressed as a percentage (%).

A relative humidity between 68% and 70% and a temperature between 20ºC and 23ºC are generally recommended for storing cigars in the humidor. This is because temperature affects humidity levels.

In cooler environments, the air’s capacity to hold moisture is lower, meaning it becomes saturated more quickly. This triggers condensation, which can appear as microdroplets (dew) inside the humidor, providing the excessive humidity environment needed for mould to grow.

This is known as the dew point, the temperature at which water vapor in the air begins to condense into water droplets (dew) if the temperature is sufficiently low.

For example, at a relative humidity of 70% (within the recommended levels for cigar preservation in the humidor) and an ambient temperature of 25ºC, the temperature at which the air will saturate and moisture will start condensing into water (dew point) is 18.6ºC.

However, with the same relative humidity of 70% and a temperature of 20ºC, the dew point at which the air can no longer hold more moisture will be 14.2ºC. At a higher temperature, like 30ºC, the dew point with that same humidity increases to 23.3ºC.

Adjusting Humidity Levels Based on Temperature

We want to emphasize that the recommended relative humidity of around 68-70% for cigar preservation should be adjusted based on the climate you live in or the ambient temperature of your home or establishment where the humidor is kept, regardless of the humidification system.

Humidors usually work with natural humidification (sponge tray) or electronic devices (like our HR6 model). In both cases, adjustments need to be made considering the ambient temperature. It is not advisable to overly wet the sponges, as they can release excess moisture. Similarly, the electronic humidification system levels should be adjusted to the ambient temperature.

Therefore, it is advisable to regularly monitor the conditions inside the humidor (humidity and temperature) and modify or readjust them if necessary. Using a hygrometer to measure humidity and even a thermometer to know the temperature can be very useful to manage the proper levels and avoid problems.

In any case, humidity should be kept below 72% inside the humidor, especially if the ambient temperature is low. It is advisable to maintain a stable and not too low temperature to reduce the risk of condensation and avoid sudden temperature changes. As we have explained in previous articles, ventilating the humidor helps avoid moisture buildup.

As a final conclusion, it should be noted that mould will grow on the cigars or on the cedar wood in the humidor when temperatures are quite low (below 18°C) or when there are very sudden temperature changes of more than 6-7°C difference.