Look on any shelf of a well-stocked beer store these days and it's apparent that the art of brewing is more diverse than ever. Even consumers well-versed in craft beer have a hard time staying on top of the array of stouts, IPAs, wheat wines, and barrel-aged Baltic porters being churned out by nearly 3,000 craft breweries across the country.

In a cavernous warehouse a stone's throw from the Mystic River, Mystic Brewery founder Bryan Greenhagen is stretching the boundaries of brewing. A former MIT researcher with a PhD in plant biochemistry, Greenhagen likes to push the edge of what yeast can do. Mystic's most complicated beer, Entropy, is fermented in four stages with four different yeast treatments. A house Trappist strain "brings out earthiness and dark fruit, amplified and rounded by a French white wine yeast." A six-month fermentation with Sherry yeast follows, and the beer is completed with an English barleywine yeast. This year-long process produces a final product weighing in at 14.5 percent alcohol by volume.

"Since the idea with our brewery was and is to bring yeast back into the brewing equation in our beers, we wanted a beer that really pushed the limits in that aspect," says Greenhagen. "Its absolutely about taking the fermentive aspect to its limits and really seeing what can be done with a beer."

A still, uncarbonated ale, Entropy does not fit into a neat category or beer style, though Greenhagen makes it clear that its still a beer. Entropy starts with malt and is not distilled. Greenhagen describes Samuel Adams Utopias as an "East Coast original" that "also pushed the limits of what a beer can be and was inspiring in our own efforts."

I pop the cork off my bottle of Entropy, and by the time I grab my glass whiffs of vanilla find my nose several feet away. The beer sits still and cloudy-brown in my glass.

A deeper sniff of my 3-ounce pour reveals sherry, vanilla, and toasted almonds. It would be fun to linger over the glass, but it's time to take a sip. Sweet figs are prominent up front, but the beer quickly diverges away from the dark fruit flavors of a barleywine and toward the dryness of a sherry. I get dry earth, toffee, white grape skin, and tobacco. The mouthfeel is not as decadently thick as a stout; this sits more delicately on your tongue.

The natural comparison here is Utopias. Entropy tastes a little younger than the 2013 version of Utopias, and that's because it is. Utopias has an alcohol content approaching 30 percent and includes barrels of beer aged 20 years or more. Greenhagen will continue to blend beer from older barrels into future batches of Entropy, but there aren't any 20-year-old barrels yet.

For proper research, I poured myself two ounces of Utopias later on and immediately noticed how much more honeyed and viscous it is. Another obvious comparison point is the price. Samuel Adams suggests $199 for a bottle of Utopias; I paid $35 for my bottle of Entropy.

Two more notes on Entropy. A small pour will go a long way, but despite the ABV, the levity of the drink makes it perfect for pairing with sweeter desserts. Also don't fret about this being an uncarbonated "still ale". There's so much going on here you won't miss the bubbles. Greenhagen suggests aging the brew for up to 20 years and watching it evolve.