[fw-formats] Tag search with zend_search_lucene

Hi,
I want to index a document that has a field called 'tags' that looks
like that : 'foo, foo bar'
The comma is the separator for each tag, so I have a tag with the value
'foo' and another one with 'foo bar'
What I want to do is to be able to retrieve the documents with certain
tag(only one tag per query), so if I search by 'foo', this document
should be hit, as well as if I search by 'foo bar', but if I enter 'bar'
as the tag, it shouldn't although it is being retrieved too.
I tried to index the field as keyword and as text(I know so it's
tokenized so it shouldn't work at all) and tried several queries with no
success.
Any tip to achieve what I want? Should I write my own analyzer?
I know the java implementation has something like term vectors and this
could probably solve the problem, but I don't if the Zend version
implements this feature...
Thanks in advance.

Regards