For proper animal nutrition it is essential that the cereals are treated and stored in a safe and respectful way of the different organoleptic properties. To increase digestibility and the ability to better assimilate proteins and fats of vegetable origin, as well as to remove germination and any anti-nutritional component, roasting of grains is essential. Thanks to the roasting the cereal acquires quality and flavor. Not only trypsin inhibitors that interfere with protein digestion are minimized, but, in the case of polygastric animals, additional bypass proteins are also generated.
To achieve best quality results it is essential to have a quality roaster in order to feed your animals with only highly nutritious and healthy cereals. But what are the aspects to take into consideration to choosing the roaster? In this article, Mecmar offers an important overview of the operation of the machines on the market, comparing the fluid bed roaster with the drum roaster, to guide you in the best choice according to your needs.
Drum roaster operation
Drum roasters represent a relatively inexpensive solution for the purchase price, but now are also the most obsolete. In fact, being the first technology invented for this type of treatment, they have a relatively simple design and operation: consisting of a rotating cylindrical drum, the heat is generated directly under the drum or through a duct. A similar type of roaster was built in Mecmar more than 15 years ago, now they have been replaced only by fluidized bed roasters.
In this machine, the grains are transported from the inlet to the outlet by rotating inside a cylinder, and absorb 25% of heat by conduction, that is from direct contact with heat, and 75% by convection, through the air flowing into the drum. Temperature measurements can be made using two indicators: one measures the actual flame temperature and the other measures the temperature of the grain inside the drum. One of the main reasons why this technology has been abandoned in Mecmar is because of the difficulty of guaranteeing a homogeneous roasting process: if too much heat is applied, overheating of the metal can lead to excessive combustion of the grains, but also to excessive speed of rotation can push the beans against the hopper and transfer too much heat to a section of the bean. In the initial part of the cylinder the grain is subject to a high heat wave (in some cases it passes through the flame produced by the burner at very high temperatures), while the beans leaving the cylinder are subject to lower temperatures, hence the difficulty of guarantee homogeneity of treatment.
Fluid bed roaster operation
The fluid bed roasters work thanks to a completely different system compared to the drum ones: they consist of a high cylinder that allows the hot air to flow evenly through a chamber, the heat is generated through convection. Grains are roasted evenly and all at the same temperature. During the roasting process cereals never encounter the flame, consequently there is no risk of carbonizing the product on one side.
The fluid bed roasters bear this name because they use a flow of hot air capable of circulating and rotating the lying grains that flow horizontally towards the outlet, in this way grains are always in motion and receive heat at 360°, in this way the roasting takes place in a controlled and uniform way. The ability to manage parameters such as the thickness of the product to be treated, the drying temperature and the residence time in the roaster allow flexibility to further optimize the roasting process.
In the comparison between fluid bed and drum roasters, the first difference is the method of heat diffusion. Drum roasters use conductive heat: in which grains are exposed directly to the flame (therefore a volume still burning) and are in contact with the hot steel of the drum, the radiative heat propagated by the overheated steel and the iron of the drum, and with convective heat, in which grains are immersed in the combustion fumes. Fluid bed roasters use only convective heat generated by a flow of hot air that passes through grains in the roasting chamber and mixes them.
The second difference concerns the movement of the cereal during roasting. The drum roasters mix the cereal by rotation, in which they are in contact with the wall for a long time and then fall vertically. The fluidized bed roasters let the hot air move the cereals stretched out and away from the flame.
A final consideration concerns costs and maintenance. The drum roasters, due to the large drum and the heating of the rotating body, can be subject to frequent maintenance, while the fluid bed roasters are simpler for cleaning and maintenance as there are two main moving parts which do not perform any effort, as the belt must accompany the product to be toasted from the inlet to the outlet. Along the way, the cereal “floats” on the fluidized bed, so there is no mechanical transport effort and electricity consumption is very low.
In comparison, it is undeniable how much fluid bed roasters represent the most innovative and safe solution for those who want to toast in a safe and advantageous way, and feed animals with quality food that, when dosed in appropriate feeding recipes, allow them to grow healthy and without requiring the use of protein supplements.
Mecmar fluid bed roasters are designed to carry out a delicate, very homogeneous and rapid treatment on any type of cereal, but also in an automated way thanks to sensors that allow you to control and optimize the roasting process. Depending on the needs, the heat can be generated by oil, gas, LPG burners or by a heat exchanger. The advantage of this solution is also contained in the ability to reduce energy costs thanks to the recovery of the hot air coming out of the machine to preheat the air that will be used for roasting.
Whatever your roasting needs, Mecmar has the right machine for you: contact us! Our team of experts will be able to advise and guide you in choosing the best roaster.