Drying Alfalfa / Lucerne: Protein, Leaf and Colour
Two types of dryers are used for alfalfa (lucerne) drying: drum dryers and horizontal dryers (often referred to as conveyor dryers, although this is not always accurate). These dryers differ fundamentally in their drying technology, but the key distinctions lie in the quality of the final product and its market value.
Drum Dryers for Alfalfa and Hay
Drum dryers have stricter requirements for the quality of the raw material at the inlet. For example, while a horizontal dryer can process alfalfa chopped to 20 cm, the product fed into a drum dryer should ideally not exceed 5 cm in length.
Additionally, the quality of alfalfa after drying in a drum dryer may be somewhat lower compared to horizontal drying technology.
Nevertheless, drum dryers remain in demand because they are less expensive than conveyor dryers and represent an older, well-established technology.
Conveyor Dryers for Alfalfa with a Stirring Mechanism
Conveyor dryers deliver significantly higher alfalfa quality. This is why, in Europe, they have virtually replaced drum dryers, despite their higher cost.
Furthermore, conveyor dryers are far more versatile than drum dryers.
Although these dryers are equipped with a stirring mechanism, there is no cause for concern. They are engineered specifically for gentle alfalfa drying, ensuring maximum preservation of quality and protein content. The stirrer features specially designed paddles that rotate to guarantee careful handling of the product and optimal results.
Comparison of Drum and Conveyor Dryers for Alfalfa
Let us look more specifically at the advantages of conveyor dryers over drum dryers.
1. Drying Temperature
Drum dryers dry alfalfa at temperatures of 250–300°C and above, which adversely affects product quality and organoleptic properties. High temperatures not only degrade the composition of alfalfa but can also alter its colour.
Conveyor dryers operate at temperatures up to 120°C, providing a far gentler drying regime that is optimal for forage production. The lower temperature prevents localised overheating and preserves the structure and nutritional content of the crop.
This alone is a compelling argument in favour of conveyor dryers — but there are further advantages, described below.
2. Degree of Chopping
For drum dryers, the product must be chopped to 5–10 cm, depending on initial moisture content. In conveyor dryers, the allowable fibre length is twice as long — up to 20 cm.
The less the product is chopped, the more protein it retains.
3. Heat Recirculation and Recovery
Some conveyor dryers, such as the Scolari 2T series, feature a two-level design with dual conveyors. Hot air, after passing through the lower conveyor, is reused to preheat and partially dry the product on the upper conveyor. This reduces gas or other fuel consumption.
Scolari also produces three-level dryers in the 3T series, which are highly popular among alfalfa exporters. The 3T models make maximum use of hot air — a particularly important advantage when drying with expensive fuels such as liquefied or natural gas.
Drum dryers are typically not equipped with heat recirculation or recovery systems, making them less energy-efficient.
4. Versatility
As already noted, conveyor dryers are suitable not only for alfalfa but also for a wide range of other products, including:
- Grape seeds and seeds of other fruits
- Pulp and peels of fruits and vegetables
- Various herbs (medicinal, aromatic and others)
- Mushrooms
- Digestate from biogas plants
- Sewage sludge
These are just a few examples of their applications.
In addition, conveyor dryers are fully adapted for drying all types of grain crops. When drying grain, a full hot-air recirculation system is implemented, ensuring low drying costs — including for maize.
5. Nutrient Retention
The decisive factor is maximum preservation of nutrients in dried alfalfa. Losses arise not only from the operating principle of drum dryers — which subject the product to continuous mechanical stress throughout drying — but also from their high-temperature regime.
By contrast, conveyor dryers dry alfalfa at lower temperatures (a gentle drying mode), which significantly improves the quality of the final product.
To illustrate this, consider the comparative analysis conducted by the University of Bologna (Italy). The data clearly show that low-temperature dehydration preserves far more nutrients than high-temperature drying in drum dryers. Furthermore, the level of digestible protein not only remained stable but actually increased.
The University of Bologna took the analysis further by comparing alfalfa dried under near-ideal laboratory conditions against alfalfa dried in a Scolari dryer. The results show that at the same moisture level of 9.84%, the content of all beneficial nutrients was very close to the ideal. Moreover, certain parameters — such as iron content and feed units — even exceeded the results obtained under laboratory conditions.
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6. Power Consumption
Drum-type dryers must not only generate a high airflow but also rotate a massive drum. As a result, both the installed and consumed power of such units is substantially higher compared to modern conveyor dryers.
7. Controlled Material Throughput
In a drum-type dryer, the product travels from inlet to outlet inside an inclined rotating drum under the force of gravity. If a portion of the product with non-standard moisture content or physical properties enters the dryer, it may move faster or slower than the bulk of the material.
In conveyor dryers, the product rests on the conveyor belt and moves at a constant, uniform speed.
Alfalfa Dryers We Supply
We supply both types of alfalfa dryers – drum dryers and conveyor dryers from Scolari (Italy), Alvan Blanch (UK), and Herbas (Croatia).
Scolari Vibratory Dryers
Italian Scolari vibratory dryers create an artificial boiling layer of the material being dried, which allows it to be blown through from all sides and effectively remove surface moisture. Suitable for materials with surface moisture, granulated products, or flowing powders.
Scolari Dryer With Movable Conveyor Belt
Horizontal dryers feature perforated steel or plastic movable floors designed for drying various materials. Airflow can be configured from top to bottom or vice versa.
Alvan Blanch Conveyor Dryer
British universal conveyor dryers for non-grain agricultural and industrial products. Thanks to their horizontal design, built-in distribution and stirring systems, they can dry a wide range of materials.
Further Reading
All our articles on drying and processing equipment
Whether you are planning a new drying facility or already operating one, this section provides useful guidance on drying and processing equipment — its characteristics, selection, maintenance, and operation.
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