We've tasted literally of dozens of cha tou in the first half of 2018. Many were good, but these were the best we had that weren't hyper old and expensive. These are made from spring 2015 harvested Bu Lang Mountain (Menghai County of Xishuangbanna) tea that was wet piled in Menghai in the summer of 2015. These have been aged close to 3 years and have developed into an incredibly complex ripe pu-erh tea. When brewed these give a deep burgundy-brown tea soup and a viscous fruity sweet taste.
Cha Tou is a kind of tea nugget that forms naturally from the pressures of compression and heat that occurs during the fermentation process. Typically during fermentation process to make ripe pu-erh there is a pile of tea about 1 meter high. It is kept wet to allow the fermentation process and the pile is turned every few days to allow for an even degree of fermentation, moving the tea from the bottom of the pile (where it is hotter and wetter) to the top of the pile where it is cooler and drier. The "cha tou" are the leaves that ball up and get stuck together. The best cha tou are ones that have not been over-fermented and are smaller in size.
**some of these will have some grey or white spores on them. If you are squeamish about spores/bacteria don't buy these!