It has been shown in the literature that automatic speech recognition systems can greatly benefit from contextual information [1, 2, 3, 4, 5]. Contextual information can be used to simplify the beam search and improve recognition accuracy. Types of useful contextual information can include the name of the application the user is in, the contents of the user's phone screen, the user's location, a certain dialog state, etc. Building a separate language model for each of these types of context is not feasible due to limited resources or limited amounts of training data. In this paper we describe an approach for unsupervised learning of contextual information and automatic building of contextual biasing models. Our approach can be used to build a large number of small contextual models from a limited amount of available unsupervised training data. We describe how n-grams relevant for a particular context are automatically selected as well as how an optimal size of a final contextual model is chosen. Our experimental results show great accuracy improvements for several types of context.