I have recently switched from carrierwave to shrine in my Rails app and i thought i follow the advice of Alan Richardson, saying when you learn something new, irregardless of how trivial it might seem to you, share it and save someone else that headache. So in the Yangah application, we upload a number of files to amazon s3 which include images, font files and css files for these fonts. However, i have found that with shrine, out of the box it was not able to correctly set the mime type for the uploaded file on s3.