For drying lettuce, centrifuging this product is the first thing that comes to mind. This is undoubtedly a good method that can be used for many products, provided the right technique is used.
However, there is an increasing market demand for delicate leafy vegetables. Moreover, lower moisture contents are desired to improve the shelf life of these products. A centrifuge cannot always meet these demands.
Sormac air drying tunnel
For these products, Sormac developed a so-called drying tunnel many years ago. This allows processing of products without damage and, if desired, moisture contents lower than 1% are possible. The result is an attractive, fresh looking product that can be kept a few days longer thanks to the low moisture content. Due to the dramatically increased demand for drying tunnels, this technique is currently enjoying a revival. Sormac has therefore developed a series of tunnels with belt widths of 400, 1,000 and 1,400 mm and lengths up to 11 metres.
How does the Sormac drying tunnel work?
Before the product enters the drying tunnel, any adhering moisture is removed on a pre-de-watering belt. This is done by suctioning, tapping and blowing. The product passes the drying tunnel as it floats between two mesh belts. The air flowing top-down is each time cooled to condense the absorbed water. Then the air is reheated to be able to absorb moisture again.
What makes the Sormac drying tunnel unique?
The Sormac drying tunnels have generous dimensions, so that the air never needs to be heated above 28°C. The evaporating moisture keeps the product very cool. Moreover, in the last part of the drying tunnel, the product is cooled back to a temperature of about 3°C if desired.
Because all air remains in the drying tunnel, the temperature of the production room is not affected and no additional room cooling is needed. And no less important: because there is no air exchange with the environment, the air in the drying tunnel remains much cleaner microbiologically. And this has a positive effect on the end product!
How is an air-dried product different?
A product dried in a drying tunnel to about 1% of adhering moisture is different in many ways:
- It looks fresh and attractive;
- Water will condense in the packages on the refrigerated shelves;
- The product is both physiologically and microbiologically in a better condition, resulting in an extended shelf life of a few days.
Does the drying tunnel only have advantages?
A superior product comes at a cost. A drawback is that the energy consumption of a drying tunnel is higher than that of a centrifuge. In addition, the tunnel requires more space and a higher investment.
Therefore a processor needs to consider whether his product needs such high-quality drying and whether his customer is prepared to pay more for a better product.