Dry on the surface but wet at the core – A persistent problem in drying and the solution from SUNSAY technology.

In the production of food, medicinal herbs, or dried agricultural products, drying is not only a process of reducing water content but also a crucial step in determining product quality, shelf life, and value. However, many production facilities still face a common but serious technical error: the product is dry on the surface but wet inside . This is not only a sensory issue but also poses significant risks in storage and commercialization.

So what causes this phenomenon? How can we completely resolve it while preserving the quality and natural value of the product? This article will help you understand the nature of the phenomenon and why the SUNSAY freeze dryer is the comprehensive solution for effectively addressing this problem.

Dry on the outside, wet on the inside – Why does this happen?

The phenomenon of a dry surface but a wet core occurs when a product is put into drying, but the moisture removal process between the outer layer and the core is uneven. Scientifically, this is the result of an imbalance between the rate of evaporation and the rate of moisture diffusion from the inside to the outside.

In the initial drying stage, high temperatures or strong airflow cause the surface layer in direct contact with the drying environment to lose water rapidly, becoming dry and hard, forming a solid crust. Meanwhile, the moisture inside has not yet escaped, being trapped by the outer crust, resulting in the core remaining wet. This process is often referred to as the “moisture barrier” phenomenon – a technical error that many traditional agricultural product drying facilities encounter.

Serious consequences will result if the problem is not addressed thoroughly.

At first glance, the product appears dry – but it actually retains high levels of moisture inside, and this leads to a series of problems:

• Post-packaging damage: When packaging while the core is still damp, the moisture inside will continue to escape, condensing into water droplets inside the packaging, creating conditions for mold and bacteria to grow.
• Inventory and export risks: Products are easily rejected by markets with strict moisture content standards, especially the EU, Japan, and the US…
• Poor user experience: The product is crispy on the outside but soft and wet on the inside, giving consumers a “falsely dry” feel, making them feel unnatural and easily suspicious of its quality.
• Loss of nutritional and sensory value: In the core, where moisture remains for a long time, fermentation or denaturation of micronutrients may occur if not treated promptly.

Where does the cause come from?

This phenomenon commonly occurs in traditional heat drying systems such as gas ovens, wood-fired ovens, and convection electric dryers… The main causes stem from:

• The drying temperature was too high from the start: This caused the outer layer to evaporate too quickly.
• Failure to control air humidity in the drying chamber leads to an imbalance in the dehumidification process.
• The hot air flow is unevenly distributed, or the manual control system is unstable.
• The product has a thick texture or is rich in sugar/starch, making it difficult for moisture to move from the core outwards.
• The drying tray design is unsuitable, limiting the contact area between the material and the airflow.

In traditional workshops, it is difficult for operators to precisely control each of the aforementioned factors. This is why SUNSAY freeze-drying technology was developed as a solution to this problem.

SUNSAY – A solution for controlling moisture loss from root to tip.

Unlike thermal drying methods, SUNSAY cold dryers use a stream of dry air at low temperatures (25–50°C) to naturally remove moisture from the product without causing thermal shock to the surface. The drying process is slow and steady, allowing sufficient time for moisture in the core to move outwards without forming a hard barrier on the outside.

This is the core difference that allows SUNSAY food heat pump dryer to completely solve the problem of surface dryness – core wetness:

• The precisely controlled flow of dry air is evenly distributed across the trays, ensuring uniform moisture removal across the entire surface and core.
• The intelligent PLC-HMI control system allows for programming temperature and humidity in stages: light dehumidification stage, stable temperature maintenance stage, and final stage.
• The closed-loop air circulation process prevents re-moisture absorption and helps reduce temperature fluctuations within the drying chamber.
• Depending on the thickness and texture of the material, the machine can be calibrated to maintain uniform moisture levels from the inside out, ensuring the product is completely dried and safe for long-term storage.

The benefits go beyond simply drying.

When the phenomenon of surface dryness but core wetness is thoroughly addressed, it results not only in an aesthetically pleasing batch of dried products, but also a comprehensive improvement in product quality and business efficiency. Products dried evenly from inside out minimize the risk of post-drying damage, thereby saving costs and shortening the error handling process.

Furthermore, achieving the optimal moisture level during drying improves packaging efficiency, prevents condensation inside the packaging, and naturally extends shelf life without the need for preservatives. With tightly controlled dryness, the product easily meets stringent export standards, paving the way for businesses to expand into international markets.

More significantly, with consistent and stable quality, your brand will gradually be positioned in the minds of customers as a reputable, professional manufacturer with products of real value.

And most importantly, it’s about peace of mind – peace of mind when delivering products to distributors, when packaging large quantities, when shipping overseas, and even when receiving feedback from end consumers. No more worries about technical errors causing reputational damage or economic losses – that’s the solid foundation for long-term growth.

SUNSAY – Maintaining quality, controlling dryness down to the millimeter.

With over 10 years of experience in researching, manufacturing, and applying drying machines in Vietnam, SUNSAY not only provides drying equipment – ​​we build the most suitable solutions for each material and each production model.

From fresh fruits, medicinal herbs, and vegetables to premium seafood, SUNSAY has partnered with hundreds of businesses to successfully address common drying issues – including the phenomenon of surface dryness while the core remains wet – to produce products that meet international standards.

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With more than 15 years of research and innovation, SUNSAY’s team of talented engineers has crafted a perfect solution for enhancing the value and preserving Vietnamese agricultural products. SUNSAY not only helps drying become faster and more efficient, but also opens up new opportunities for the sustainable development of the agricultural industry.

With competitive prices and outstanding quality, SUNSAY has affirmed its position as the ideal partner for those who love to improve the quality of agricultural products. SUNSAY’s freeze dryer not only preserves the flavor and nutrition, but also preserves the freshness and appeal of the fruit. Not only that, SUNSAY also demonstrates perfection through the design of the fruit drying factory to meet the growing needs of customers.

Come to SUNSAY to experience our difference and professionalism. We are committed to providing completely free product sample drying services, helping you feel completely secure about the quality and effectiveness of SUNSAY cold dryers. We not only contribute to enhancing the value of Vietnamese agricultural products but also promote the development of the domestic agricultural industry.

For detailed advice, please visit website: kynghexanh.com.vn or immediately contact Hotline (Zalo): +84 935.995.035 or switchboard number: +84 94.110.8888 for support.

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