Substances & Recipes - multiple indices or not?

My users search for two different types of foods: Substances (e.g ‘peas’) and Recipes (e.g. ‘pea soup’). The most important data field for both is the name/title. Some Substances also have a brand (e.g. ‘Cambells’), Recipes don’t.

I want to offer my users a single field for searching all foods. The difference between Substances and Recipes is mostly semantic for the users but especially in tie situations, a Substance is generally more relevant to the user than a Recipe. Hence, that’s something I want to be able to configure.

My first task is to decide whether I should have separate indices for Substances and Recipes and use search-time merging of results or have a single Foods index (aggregating the data is not an issue). What do you recommend?