West Michigan Beer Tours
Based in Kalamazoo, MI West Michigan Beer Tours does public and private brewery tours all over Western Michigan. This is a new company but they have a few tours under their belt already and seem to do a public tour every few months at least hitting new breweries in large groups with knowledgeable guides. They seem to stick with visiting a smaller number of breweries but promise to provide time at each one to sample the beers and get a feel for the breweries.
According to their website:
West Michigan Beer Tours offer a variety of public tours. A typical public bus tour will last approximately 5 hours and transportation will be 29 person mini-coach buses. Most tours will include:

3 Brewery Stops
Tour director knowledgeable in both the beer industry and our local area
Introduction to brewery owners and/or brewers
Tours of their facility
Sample at each brewery

West Michigan Beer Tours is dedicated to providing beer lovers with fun, flavorful and relaxing tours. We encourage every passenger to drink responsibly and have a designated driver. After each tour we will also provide access to a local taxi service. While we encourage everyone to purchase beer at the breweries to take with you, we do not allow any consumption on the buses.