After the yerba mate trees have reached 4-6 years old, they are ready to begin being harvested. At this point, cultivated yerba mate trees are around 4-5 meters tall and of almost the same diameter, native yerba mate trees may reach up to 15 meters tall and 3-4 in diameter. The harvest occurs once every 2 years, in a rotating system, where only a part of the plantation is harvested at a time, providing a constant supply of leaves and giving the yerba mate trees 2 years to replace the growth lost in the pruning. The native yerba mate trees may be harvested at any time of the year, but only every 3 or 4 years, unlike the cultivated yerba mate trees which are harvested at the end of winter.
The workers that gather the yerba mate leaves are from experienced families, being trained to harvest the yerba mate, pruning the trees the right way, a skill that has been passed down in these families for many years. They spread a white nylon tarp or sheet on the ground around the yerba mate tree to prevent prolonged contact with the ground and cut the branches. They then cut out the larger sticks leaving only the smaller branches and bundle them up in the tarps, loading them for transport to the processing plant.
Special care is applied so that the tree is not hurt during the harvest. Shortly after harvest the yerba mate trees put out new shoots, which is the growth harvested 2 years later. The harvest time does determine the flavor of the yerba mate, as well as its nutritional properties, especially its stimulant content. Yerba mate leaves gathered in February and March tend to have a notably higher stimulating effect than the leaves gathered in September, but they also tend to have a bitterer flavor, as the new buds are then emerging.
When they arrive at the yerba mate processing plant, the branches are spread on a conveyor belt that carries them to the hopper of what is called in Portuguese a Sapecador (Saw-pa-caw-door). There the branches fall through the leaping flames of a fire. This fire is made our proprietary Cleanheat System, so that the yerba mate leaves do not come in contact with the dense smoke that results in traditional wood fires. This process heats the surface of the leaf to 400C for fractions of a second, breaking a thin film of protective enzymes that coats the surface of the leaf. These enzymes, peroxidase and polifenoloxidase would otherwise hinder the evaporation of the water content and cause oxidation in the leaves during the remaining drying process, rendering it useless. This process also removes microorganisms that could otherwise cause fermentation and contamination in the product. The process does not superheat the inner part of the yerba mate leaf, leaving the nutritional properties intact.
The yerba mate leaves and branches then roll through a spinning cylinder through which Cleanheat is blown, maintaining the leaves under a controlled temperature to initiate the dehydration. When they leave this first cylinder the leaves and branches are crushed to reduce them to a size that will quicken the dehydration. They then enter the dehydration cylinder, a triple spinning cylinder where they travel back and forth three times, all the while being drafted with warm air from our Cleanheat. The temperature in this cylinder is lower than the previous one, enabling an even drying of the yerba mate leaves.
After running the dehydration system the yerba mate leaves are cut, sifted and remixed to match the specific cuts specifications of leaf size, leaf powder percentage etc. We combine percentages of native yerba mate and cultivated yerba mate to reach the desired flavor.
The yerba mate then sits for at least 24 hours to let the rest of the humidity evaporate. It then is packaged in 2.5kg and 340g triple layer bags for prolonged freshness, or in larger bags for the bulk market. In our triple-layer bags, the yerba mate can be maintained in a stable condition for more than two years, maintaining intact the nutritional properties. The triple-layer package serves as a barrier to oxygen and light, the main sources of oxidation.
Studies have shown that the properties of yerba mate suffer little variation during this process; the mineral percentage actually concentrates due to the evaporation of the water. There were variations observed in yerba mate that had been exposed to the smoke of the traditional log fires used to dry yerba mate. These we have stabilized with our Cleanheat system, in order to preserve the full nutrition of the original leaf.
Note: This description fits the yerba mate grown and processed by Mat Factor only and should not be considered fitting to describe processing or cultivating of yerba mate by other companies or groups.