First of all you should generate one guid per one item:
var docs = {};
for(var i=0; i<100; i++){
var guid = guid.raw();
docs[guid] = {
"iteration" : i,
"category": "North American Ale"
}
}
Then you can use setMulti (see docs here) to store all your data in one request.
db.setMulti(docs, {}, function(err, results) {
if (err) throw err;
});