How High is Too High? Humidity and Produce Safety

, Produce Safety Technician


Many crops thrive in high humidity settings, both in growth and storage. It’s no surprise, then, that many produce growers intentionally create high humidity environments on their farms for growing or storing produce, such as in storage rooms for apples or indoor growing rooms for mushrooms. Keeping humidity high in key areas on the farm can be a good thing – but are there food safety risks to consider, as well?

The answer depends on whether humidity is allowed to create condensation and drip onto produce. There is nothing in the Produce Safety Rule to stop a grower from using practices that increase the humidity in areas where covered produce is being grown, harvested, packed, or held. However, when the humidity of a space is allowed to reach 100%, water vapor condenses, and dripping occurs. This dripping, or condensate, could be a source of contamination for any produce it comes into contact with, and is a food safety concern.

Condensation is problematic for food safety because bacteria or germs that may be on surfaces that would normally not touch produce and therefore not pose an immediate concern – such as ceilings, ducts, fixtures, or walls – now have the opportunity to contaminate produce and food contact surfaces through dripping. If condensation is allowed to form and drip from any surface in a covered area, those surfaces should be maintained in a sanitary condition, as indicated in section 112.126(b), subpart L, of the Produce Safety Rule. Condensate from surfaces that have not been cleaned and sanitized will render any produce it touches as suspected of adulteration, and therefore unsalable and must be thrown out.

Compared to cleaning and sanitizing the ceiling of an intentional high humidity room, preventing drip or condensate in the first place may be preferable – and more manageable and better for business. Remember, the key is to avoid humidity from reaching 100% so that vapor cannot condensate. Here are the top three considerations for managing humidity:

  • Measure humidity levels. A hygrometer is the easiest way to measure humidity. There are many options available, from analog to digital, wireless to plug-in to wall mounted. There are even smartphone apps to connect with devices to keep track of humidity from anywhere. Knowing the current humidity level is essential for being able to control it.
  • Control humidity levels. A hydrostat can keep the humidity within a preset range. Having a hygrometer with an alert system if humidity dips below or rises above a desired range can be helpful in knowing when to take action to prevent condensation.
  • Choose the right humidifier. Some humidifiers may create droplets, or atomize water, defeating the purpose of trying to avoid condensation. Fogging humidifiers may be better suited for use in covered areas. MSU Agrifood Safety has DIY guides for building a fogging humidifier available free of charge.