By default, Webob's Response object assumes a default character set of utf-8.  It doesn't like when you don't give it Unicode:

https://github.com/Pylons/webob/blob/master/webob/response.py#L414

The templating internals of Pecan are going to be generating Unicode here, but in the event that you *don't* want to return Unicode, you could modify the `pecan.response.charset` and `pecan.response.body` manually in your controller (I'm going to add a test for this example in another commit).