Online discussions such as a large-scale community brainstorming often end up with an unorganized bramble of ideas and topics that are difficult to reuse. A process of distillation is needed to boil down a large information space into information that is concise and organized. We take a system-augmented approach to the problem by creating a set of tools with which human editors can collaboratively distill a large amount of informal information.Two design principles, which we will define as incremental diagenesis and incremental summarization, help editors flexibly distill the informal information. Our system, Arkose, is built as a demonstration of these principles, providing the necessary tools for distillation. These tools include a number of visualization and information retrieval mechanisms, as well as an authoring tool and a navigator for the information space. They support a gradual increase in the order and reusability of the information space and allow various levels of intermediate states of a distillation.