config_application.rb

    config.paperclip_defaults = {
      :storage => :s3,
      :s3_credentials => {
        :bucket => 'BUCKET',
        :access_key_id => 'S3_KEY',
        :secret_access_key => 'S3_SECRET'
      }
    }

config_initializers_spree.rb

Paperclip::Attachment.default_options[:s3_protocol] = "https"
Spree::Image.attachment_definitions[:attachment][:styles] = ActiveSupport::JSON.decode('{"mini":"48x48\u003E","small":"100x100\u003E","product":"240x240\u003E","large":"600x600\u003E"}').symbolize_keys!
Spree::Image.attachment_definitions[:attachment][:path] = " /#{Rails.env}/:id/:style/:basename.:extension"
Spree::Image.attachment_definitions[:attachment][:url] = '/spree/products/:id/:style/:basename.:extension'
Spree::Image.attachment_definitions[:attachment][:default_url] = ''
Spree::Image.attachment_definitions[:attachment][:default_style] = 'product'

Why the JSON.decode line?