You could make you own essence, like Marc suggested.
Or you use the EssenceHtml. That just stores binary/blob data in the database.
You easily can override the view partial for that essence type:
app/views/alchemy/essences/_essence_html_view.html.erb
Then you would process the output:
<%= RedCloth.new(content.ingredient).to_html %>
The editor partial is:
app/views/alchemy/essences/_essence_html_editor.html.erb
Then you could add an textile editor to all editor views.
But making an own essence would be best way.
Because then you could use EssenceHtml and EssenceTextile aside in the same project.
That should work.
Regards
Thomas