When fresh fruits and vegetables are harvested, they embark on a journey through the supply chain—from farms to markets to your table. However, this journey comes with challenges: keeping the produce fresh, maintaining its quality, and minimizing losses. While much focus is placed on temperature management, relative humidity (RH) often gets overlooked. Yet, it plays a critical role in reducing weight loss and preserving the post-harvest quality of fresh horticultural produce.
Weight loss due to water evaporation is one of the primary causes of post-harvest deterioration. This blog explores how humidity impacts weight loss, shares data-driven insights for different crops, and outlines practical strategies to optimize humidity during storage.

Understanding Relative Humidity

Relative humidity (RH) is a measure of the amount of water vapor present in the air relative to the maximum amount the air can hold at a given temperature. In the context of post-harvest storage, higher RH levels help retain moisture in fresh produce, slowing the rate of water loss.
Fruits and vegetables are made up of 70–95% water, and after harvest, they naturally lose moisture through their skin. If the surrounding air is dry (low RH), water loss accelerates. High RH slows this process, keeping the produce fresh and marketable for longer.

Effects of High Humidity on Fresh Produce:

1. Prevents Shriveling: High humidity maintains the water content of produce, preventing visible signs of drying such as shriveling and wilting.
2. Retains Market Quality: Texture, appearance, and nutritional value are better preserved.
3. Minimizes Economic Losses: Reduced weight loss translates to more produce available for sale and better profitability.

The Data: How Humidity Affects Weight Loss

Extensive research has shown the relationship between RH and weight loss for various horticultural crops. Below are key findings from the FAQ document:

Commodity	Storage Temperature (°C)	Storage Humidity (%)	Storage Duration	Weight Loss (%)
Tomato	15	41-52	16 Days	7-9.3
		88-92	16 Days	2.6-4
Cabbage	1	75	4.5 Months	20.2
		85	4.5 Months	14.9
		100	4.5 Months	2.6
Lettuce	0-2	70-72	2 Days	12.4
		95-98	22 Days	4-5

Key Insights:

• Tomatoes: At low humidity (41–52%), tomatoes lose up to 9.3% of their weight in 16 days. At higher humidity (88–92%), this loss is reduced to just 4%.
• Cabbage: At 75% humidity, cabbage loses 20.2% of its weight over 4.5 months, but at 100% humidity, the weight loss drops drastically to just 2.6%.
• Lettuce: At 70–72% RH, lettuce loses 12.4% of its weight in just 2 days. However, at 95–98% RH, it stays fresh for up to 20 days, with only 4–5% weight loss.

These numbers demonstrate the importance of maintaining optimal RH levels for each type of produce to minimize water loss and extend shelf life.

How Humidity Impacts Different Types of Produce

Different fruits and vegetables have varying tolerances and requirements for RH. Here’s a closer look at how humidity affects key categories of produce:

1. Leafy Greens (e.g., Lettuce, Spinach)

• Leafy greens are highly sensitive to water loss due to their high surface area and thin outer skin.
• RH should ideally be between 95–100% to prevent wilting.
• Low RH leads to rapid wilting, discoloration, and loss of crispness.

2. Root Crops (e.g., Carrots, Potatoes)

• Root crops tolerate slightly lower RH levels, around 90–95%, but still benefit from high humidity.
• High RH reduces weight loss and helps maintain texture.

3. Fruits (e.g., Tomatoes, Peppers)

• Fruits like tomatoes require RH levels of around 85–90% to maintain their water content without encouraging mold growth.
• Excessively high RH for fruits can cause surface condensation, which may lead to fungal infections.

4. Brassicas (e.g., Cabbage, Broccoli)

• Cabbage and broccoli require very high humidity levels (95–100%) to prevent dehydration.
• Prolonged storage at low RH can cause outer leaves to dry out and lead to weight loss.

Economic and Quality Impacts of Humidity

Weight Loss and Revenue

Weight loss directly translates to financial losses for farmers, distributors, and retailers. For instance:

• A 10% weight loss in a shipment of tomatoes can significantly reduce the quantity available for sale.
• High RH storage ensures that more produce reaches the market in sellable condition.

Quality and Consumer Appeal

Humidity not only impacts weight but also affects appearance and texture:

• Wilting or shriveling due to water loss makes produce less appealing to consumers.
• Proper RH storage maintains the vibrant colors, firmness, and crispness of fruits and vegetables.

Best Practices for Humidity Management

1. Maintain Optimal RH Levels

• 85–100% RH is ideal for most fruits and vegetables.
• Use humidifiers or misting systems in cold storage facilities to maintain high humidity levels.

2. Monitor Humidity Regularly

• Install hygrometers or RH sensors in storage areas to track and adjust humidity levels as needed.
• Use automated systems for consistent humidity control.

3. Use Appropriate Packaging

• Perforated plastic films can help retain moisture without causing condensation.
• Wax coatings on certain fruits (e.g., apples) can reduce water loss.

4. Combine Humidity with Temperature Control

• RH works best when paired with optimal storage temperatures. Low temperatures slow respiration, while high RH prevents water loss.

5. Manage Humidity During Transit

• Ensure that trucks and transport systems are equipped with cooling and humidification mechanisms.
• Avoid exposing produce to dry air during loading and unloading.

Challenges of High Humidity

While high RH is beneficial, there are potential challenges

1. Condensation: Excessively high RH combined with poor ventilation can cause condensation on produce surfaces, encouraging fungal growth.
2. Fungal Infections: Certain crops are prone to mold at very high RH levels.
3. Energy Costs: Maintaining high RH in cold storage can increase energy consumption.

These challenges can be mitigated through proper ventilation, regular monitoring, and careful calibration of RH and temperature settings.

Conclusion

Humidity plays an essential role in preserving the post-harvest quality of fresh produce. By minimizing weight loss and maintaining water content, high RH levels ensure that fruits and vegetables remain fresh, nutritious, and marketable for longer periods.

However, achieving the right balance between humidity, temperature, and ventilation is key to success.

For farmers, suppliers, and retailers, investing in proper humidity management is not just a way to reduce losses—it’s an opportunity to deliver better-quality produce to consumers while maximizing profitability.

Sources

• Chilson et al., 2011. "Shelf Life of Cluster Tomatoes Stored at a Non-Chilling Temperature and Different Relative Humidity Levels." Proc. Fla. State Hort. Soc.
• Pendergrass & Isenberg, 1974. "Effect of Relative Humidity on Cabbage Quality." HortScience
• M.V. Agüero et al., 2011. "Lettuce Quality Loss Under Conditions that Favor the Wilting Phenomenon." Postharvest Biology and Technology, Vol. 59, Issue 2.