A search form with 3 tag fields… how to?

Hello, I hope my english is good enough to describe what my problem is 😉 So lets try.

I tag my custom post types, for example

Post 1: meat, spicy, onions
Post 2: fish, spicy, mushrooms
Post 3: meat, soft, mushrooms

Now i create a search form with 3 tag fields and hide the tags i dont need in the dropdown. For example:
Tag search field 1: remove tags: spicy, soft, mushrooms
Tag search field 2: remove tags: fish, meat

Now i want my users to perfomr the following search:

FIrst select for example meat or fish
then in the second dropdown select spicy or soft
and in the third mushrooms or onions

I select the first one from the dropdown and everythin is fine … he shows all the right posts.
NOW the PROBLEMS start:
when I choose something from the second dropdown it resets the first and ignores that and shows all posts with the tags from this field.

I hope you understnad what the problem is …
Anything I can do to make this work?

What I want is for example:
First dropdwon selected: meat than second dropdown spicy = result Post 1.
Now i get as a result Post 1 and Post 2 because he just count what i selected in the last tag dropdown field…

Thanks so much for your help,
greetings,
thomas