Seems like your search uses OR, not AND. So adding more ingredients broadens the search rather than narrowing it. That seems kind of useless... adding just a handful of ingredients would end up matching basically all recipes.
Edit: And if you click the star a second time it tags it as "this recipe must not include this ingredient", which would be helpful for people with allergies (or picky eaters).
And this is a prime example why icons without labels (in this app, there are no tooltips either which is even worse) are useless.
Star as in... favourite ingredient? save ingredient to some list? wut...?