In the summer of 2015, I traveled to Argentina and spent a week traveling through the region that produces most of the world's yerba mate visiting a many producers as possible. One of the first things the folks at Monte Carlo told me was "we are not cheap", and after touring their production I found out why.
The company, Monte Carlo Limitada, is a cooperative that supports many small farmers in the central growing area of yerba mate, and they have been at it for over 85 years. There is a lot of community pride that goes into belonging to this remarkable group.
The yerba mate is always naturally stationed for at least 18 months. Most producers today "speed station'" the yerba mate in large heated buildings from four to twelve weeks, and they will tell you there is no difference in the taste. I totally disagree, I tasted everybody's brand over that week and the Aguantadora was the best. It was not as dry, or bitter, the flavor lasts a very long time, and it gets sweeter the longer you drink it.
The milling process is the most sophisticated I have ever seen. Most producers break the yerba down into three components, stems, leaf and dust, then blend them back together according to their formulation. At Monte Carlo the yerba is separated into five different components. Two different stem sizes, two leaf, and one dust. This allows for a remarkable amount of control when the final product is put together. You can see and taste the difference.
This one of the most premium brands on the shelves in Argentina. We purchased directly from Monte Carlo, and with the generous help from an importer friend from Argentina we got this into the US at a very nice price. This is a must try for any yerba mate enthusiast.