Yeast is really the hidden ingredient in beer. I think it's safe to say that it is the part of the holy quadrilogy that is least talked about. OK, people might bandy about some talk of brett, erroneously conflating brett with sour beers (sure, it's a part of most sour beers, but the sourness is usually derived from lactobacillus - see here for what happens when the lacto runs wild). But you have hopheads, mild afficionados, and people who enjoy a Burton snatch, but I've never heard people express a preference for beer that has been fermented with a certain strain of yeast. Largely yeast is thought to be top-fermenting, bottom-fermenting, or wild.
The importance of yeast was brought home to me this evening when I had a bottle of Lagunitas Little Sumpin' Wild (8.85%abv). I've had a couple of Lagunitas beers recently. My good friend G brought a couple back from his trip to the USA, and I had a bottle of Little Sumpin' in the cellar, waiting for the right moment, which was now.
The bottle of Lagunitas Hop Stoopid I had a couple of days ago was good, but this bottle of Little Sumpin' Wild was great. Like an amped-up version of Little Sumpin', Hop Stoopid was big, chunky, malty and hoppy, with all of these things turned up to full volume. The malt was toffee, the hops were spice and marmalade, and to be honest, it was all a bit tiring. The Little Sumpin' Wild is just as full, just as punchy, but has some elegance to it. On the label it claims to be fermented with the Westmalle yeast strain. Having drunk Westmalle many times, I can't see any similarity, but what I will say is that this beer has gained character by having things taken out. The malt sweetness is present, but it is greatly reduced. The hop character has been released from playing a to-and-fro with a toffeeish malt character, and is left free to rampage across the palate in the same way as the hops do in Flying Dog's Raging Bitch (terrible name, great beer) and Green Flash's Le Freak.
There's a clean precision to this beer that you don't often find. It reminds me of two things; one is when I was lucky enough to visit the Italian wine estate Allegrini, and I tried their top wine 'La Poja'. I could only describe it as 'incredibly detailed'. It felt like someone was writing on my tongue, spelling out the word 'classy' across my tastebuds. The other comparison is that it's like a record that has been really well-produced; the work of the producer should be unobtrusive, and yet immediately apparent to anyone who looks for it. Quite often, the best producers turn things down in the mix, giving them their own space in the equalised mix, rather than turning things up and adding extra effects. Little Sumpin' Wild is like that; the yeast has worked to create more space on the palate, more space to allow your brain to identify the separate taste sensations.
But like a great piece of music, you don't need to analyse it. It's just a great beer.