Introduction

Condensation in your microgreen packaging is both unsightly and bad for the product's shelf life. Today we’re going to discuss how to minimize condensation in the most efficient way possible. Many people online propose methods for minimizing condensation that could work better than what we’ll discuss. However, what I propose is the most efficient and cost-effective method because it’s based on the science of temperature, humidity, and condensation.

Too Long, Didn’t Read (TLDR)

Condensation appears in your packaging because you’re trapping moisture-laden air inside with the microgreens. When you put the sealed container in your fridge, the air inside it cools. Cold air can’t hold the same amount of moisture as warm air. The water vapor condenses into drops, preferring the least insulated surface - the underside of the lid. Mitigating condensation is as simple as packing the microgreens in a smaller container. Don't pack the microgreens too tight, or you'll damage them. Less trapped air means less moisture.

Defining Terms

Let’s define a few words to cover our bases.

• A measure of temperature reflects the average kinetic energy of the particles in a substance. As temperature increases, the motion of these particles also increases. Absolute zero is the theoretical point at which molecular motion ceases.
• Humidity is the concentration of water vapor present in the air. Humidity plays a crucial role in how we perceive temperature.
  • Absolute Humidity - Measures the actual amount of water vapor in a given volume of air, usually expressed in grams of water per cubic meter of air.
  • Relative Humidity - Expressed as a percentage, indicates the current amount of water vapor in the air relative to the maximum amount that the air can hold at a specific temperature. For example, if the relative humidity is 100%, the air is fully saturated with moisture, leading to conditions such as rain or fog.
  • Specific Humidity - The ratio of the mass of water vapor to the total mass of air - including both dry air and water vapor. Expressed in grams of water vapor per kilogram of air.
• Condensation is the process by which a substance transitions from a gaseous state to a liquid state. The transition occurs when the gas cools and loses heat or thermal energy, causing its particles to slow down. As the particles slow down, attractive forces among them increase, leading to the formation of liquid droplets.
• The dew point is defined as the temperature at which air must be cooled to become saturated with water vapor, leading to condensation. When the air temperature drops to the dew point, the moisture in the air condenses into liquid water, forming dew. At the dew point, the air cannot hold any more moisture in vapor (gas) form.

Basic Assumptions

Like defining the above terms, I’m going to make a few assumptions here to make the ensuing explanation easier. I’m going to assume you’re using packaging that’s airtight and waterproof. Waterproof generally means it’s made from plastic/petroleum or a plastic-like substance. A primary example of a plastic-like substance is polylactic acid (PLC). PLA packaging is made from plants and it’s commercially compostable. However, PLA is indistinguishable from PET and other petroleum-based packaging to the average consumer. PLA has almost all the same features as PET, like being waterproof.

Why are we assuming these two things?

This blog focuses on how to minimize condensation inside your packaging. Condensation can’t form, at least not effectively, when the packaging is not airtight. Vented packaging will also dry out the microgreens because of the constant air exchange. Constant air exchange is a greater detriment to microgreen shelf life than condensation. Why waterproof? If the packaging is not waterproof, the condensation that does form, even in the optimal scenario, will degrade the packaging. Degradation of the packaging is also a greater threat to shelf life than condensation.

So, we’re going to assume your packaging is airtight and waterproof.

How Does Condensation Form

Now that we’ve defined important terms and established the initial conditions, let’s talk about how condensation forms. We’ll start with a scenario we’re all familiar with. You take a cold bottle of Coke out of the fridge on a warm day to drink. Perplexity, an AI-powered research and conversational engine, describes what happens to the Coke.

• Initial Conditions:
  • The Coke bottle is cold (4°C or 39°F) from being in the refrigerator. The surrounding air is warm (30°C or 86°F) and has a certain amount of water vapor in it.
• Temperature Difference:
  • When you take the bottle out, there's a significant temperature difference between the cold surface of the bottle and the warm surrounding air.
• Relative Humidity:
  • The warm air has a certain relative humidity, let's say 60%. This means the air is holding 60% of the maximum amount of water vapor it can hold at that temperature.
• Air Cooling Near the Bottle:
  • The air immediately surrounding the cold bottle begins to cool rapidly when it comes into contact with the bottle's surface.
• Increase in Relative Humidity:
  • As this layer of air cools, its relative humidity increases. Remember that cooler air can hold less moisture than warmer air. The relative humidity of this cooling air layer around the bottle rises quickly, approaching 100%.
• Dew Point:
  • When the air reaches 100% relative humidity, it's at its dew point - the temperature at which water vapor begins to condense into liquid water.
• Condensation:
  • Once the air in contact with the bottle surface cools below its dew point, water vapor in the air condenses into liquid water droplets on the bottle's surface.
• Visible Effect:
  • These water droplets are what you see forming on the outside of the Coke bottle.

This process continues as long as the bottle remains colder than the dew point of the surrounding air. As the bottle warms up, the condensation process will slow and eventually stop.

Thanks, Perplexity! Well said.

In summary, condensation forms when the air cools to a temperature where it can no longer “hold” the moisture in a gaseous form as water vapor. This happens because the air molecules lose energy. The space between the air molecules gets smaller, leaving less room for the water molecules. Okay, let’s bring everything together now for the real discussion. What happens inside your packaging when condensation forms, and how do we minimize the condensation?

Minimizing Condensation

The air in your farm is not perfectly dry. The air likely has a relative humidity of 40-70%, which means it’s holding a certain volume of water as a gas. The air is likely between 65-80°F. You cut the microgreens and place them in your container. You close the airtight container, trapping that moisture-laden air along with your microgreens. Based on how many microgreens you put in that container, you’ll have more or less trapped air. If you put two ounces of microgreens in a 16 oz. container, there won’t be much space left over for air. If you put the same two ounces of microgreens in a 32 oz. container, there’s going to be significantly more trapped air. More trapped air means more trapped water vapor. As we learned from the Coke example above, when you put the container in your refrigerator, you change the conditions. The air inside the packaging cools to 34-40°F. 36°F air can’t hold onto the water vapor like 72°F air. The moisture in the air condenses, but where? On the underside of the lid, blocking the consumer's view of your microgreens. Why the underside of the lid? Even if you don’t push down and pack in the microgreens when filling the containers, they’ll settle into the bottom. Gravity compresses the microgreens slightly. So, the bottom 90% of the container is mostly microgreens, and the top 10% is mostly air. With all the moisture-laden air near the top of the container, the most accessible and least insulated surface is the underside of the lid. This explanation helps us understand two strategies for handling condensation. One is smart, free, and looks good to consumers. One is costly and looks bad to consumers. Let’s start with the latter.

Paper towels, silicone packs, and any other form of moisture-wicking product are all ill-fated attempts to control moisture. First, they cost money. Objectively, we want to avoid unnecessary purchases whenever possible. Second, regardless of whether you place these items at the top of the packaging or the bottom, they’re not appealing to the consumer. If you must use them, place them on top of the microgreens. That's where the condensation forms - the underside of the lid. Unfortunately, the moisture-absorbing device will also be much more apparent and unsightly for the consumer than when placed at the bottom. The alternative option? Pack your microgreens into the smallest container possible, for their volume. Don't go so far that you damage the microgreens. When you put the microgreens in the smallest possible container, you leave the least amount of room for the moisture-laden air. Less air equals less moisture.

Other Strategies

I’ve seen a handful of other strategies mentioned online for reducing condensation. Let’s explore each one.

• “Pack the microgreens, but don’t close the lid. Place the container in the refrigerator, and then seal it later, after the air has cooled.” This method gets points for accuracy. If you close the container before putting it in the fridge or after, you’re trapping the same volume of air. If you trap cold air, though, you trap less total moisture. Less moisture equals less condensation. However, there are two problems. First, refrigerators create airflow within the unit to prevent warm spots. An open container of microgreens exposes the fragile plants to constant air movement. It will dry out the product and reduce their shelf life. Second, you’re adding a ton of labor to the packing process. Instead of packing the product, sealing the lid, and placing it in the fridge, you now have three more steps. Take the container back out of the fridge, seal it, and place it back in. It sounds trivial for 5-50 containers, but it’s going to skyrocket your labor costs as you scale. Also, if you’re taking the container out of the fridge to finish sealing it, you’re still sealing in high-moisture air.
• “Pack and seal the microgreens. Place the container in the fridge, and then ‘vent’ the lid later.” In other words, pack the product as normal, but briefly open the lid after the product has cooled in the fridge. Going back to open and reseal the lid won’t do much for condensation. By the time you vent the container, any moisture will have condensed. You would also need to use a paper towel to wipe off the existing condensation. This method is even more labor-intensive than the last.
• “Harvest the microgreens into a bin. Place the bin in the fridge to cool down the product, and then take the microgreens out to pack later.” We do this sometimes at Piedmont Microgreens, but it's not to reduce condensation during packing. We will harvest blends into big totes, put a lid on the tote, and place it in the fridge. We do this only when the packing team can’t keep up with the harvesting team. We want to keep the product cool while the packing team catches up. Otherwise, this method also doesn’t do anything for condensation during packing. If you take the bin out of the fridge to pack the product, you're still sealing the container with the farm's high humidity air.
• “Don’t water your crops 24 hours before harvest.” Again, it's a sound approach. However, it's general farming advice as much as it is advice for preventing condensation. Moisture is the enemy of shelf life. Packing wet microgreens will reduce the shelf life. Packing wet microgreens will add moisture to the container, which will worsen your condensation problems. You don’t need to stop watering 24 hours in advance of harvest. You simply want your microgreens to be well hydrated without being externally damp.
• Advice I’ve never seen suggested, but could help, is to reduce the relative humidity (RH) levels in your farm. My farm is far too humid right now - 60-75% RH. If we could lower the RH levels near our pack table to 50%, the air trapped in the packaging would have less water vapor. I'd like my farm to be between 45-55%, but it has been a challenge.

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