This paper presents the JBraindead Information Retrieval System, which combines a free-text search engine with online Formal Concept Analysis to organize the results of a query. Unlike most applications of Conceptual Clustering to Information Retrieval, JBraindead is not restricted to specific domains, and does not use manually assigned descriptors for documents nor domain specific thesauruses. Given the ranked list of documents from a search, the system dynamically decides which are the most appropriate attributes for the set of documents and generates a conceptual lattice on the fly. This paper focuses on the automatic selection of attributes: first, we propose a number of measures to evaluate the quality of a conceptual lattice for the task, and then we use the proposed measures to compare a number of strategies for the automatic selection of attributes. The results show that conceptual lattices can be very useful to group relevant information in free-text search tasks. The best results are obtained with a weighting formula based on the automatic extraction of terminology for thesaurus building, as compared to an Okapi weighting formula.