C (cgggcc), 135 133 bytes
Expects ingredients and request as command line arguments (the last one is the request). The return value of the program is the result.
l[128],n;char*a;main(c,v)char**v;{for(++v;c---2;)for(a=*v++;*a;++l[*a++]);for(a=*v,n=l[*a];*a;++a)n=*a-32&&l[*a]<n?l[*a]:n;return n;}