How to handle "or" possibilities in MongoDB
In cases where there is a legitimate option to use a substitute ingredient you can do one of several things, all involving storing the option in the ingredients array.  One way could be to add a field to an array element as "allowedSubstitutions": "different liquor" another way would be to turn "ingredient" into an array which lists possible different acceptable ingredients.

However, in case of a tricky martini drink, I would strongly encourage you to store two separate drinks, one called "Martini" and the other called "Vodka Martini" otherwise known to purists as "not really a martini" :)

The real key question is how will you be querying this collection - with flexible schema the way you use the data will usually drive the way you structure its storage, not the other way around.