The mouthfeel of beers is one of the more complex aspects of brewing. I often see it simplified as final gravity equals body. Sure mashing toward the upper-end of the saccharification range results in more alpha amylase activity, which produces a higher proportion of unfermentable dextrins, which in turn leaves both a higher final gravity and a thicker body. However, this is not the same as using a lower attenuating yeast strain, which will leave a higher percentage of fermentable sugars behind. Assuming identical original and final gravities, a hotter mash will produce a beer with more body, while a less attenuative yeast will produce a beer with more residual sweetness.
Carbohydrates aren’t the only source of body in beer however. Proteins from the malt and glycerol from the brewer's yeast are also options for enhancing body. Beta glucans, a type of soluble fiber, gets a “maybe.” While grains that contain beta glucans (like oats) tend to create a silky body, there hasn’t been enough study yet (to my knowledge) to conclusively state that beta glucans are the source.
Carbonation plays a tricky role. In a beer that has a thick body already, I find that higher carbonation wrecks the mouthfeel. There are few things more disappointing than an over-carbonated imperial stout for example. However, for a beer that is thin, higher carbonation can actually improve the body by distracting from the watery mouthfeel. Think gueuze or Berliner weisse. Tannins from oak play a similar role, a small amount can enhance body, while excess leave a rough dryness.
All this is to say that despite a relatively high final gravity (1.017), and moderate-low carbonation, the body on my second batch of Scottish stout didn’t reach quite where I wanted it. Could it be excessive oak tannins? Or was it the lack of protein from the highly-modified Maris Otter? Or maybe my expectations are too high for a beer that is only 5.4% ABV? Otherwise it is a very enjoyable beer, and hopefully I’ll get just a bit closer next time.
90/- Scottish Stout #2
Appearance – The head is a stout-appropriate tan, and wonderfully dense, sticky, and lasting. The body is black, with only a hint of ruby at the bottom where the light can make it through. Held at an angle the beer looks to have dropped pretty clear in the keg.
Smell – The nose is lightly roasted coffee to start. Nothing reads burnt or charcoal (although the fireplace is adding a hint of smoke). There is a deeper maltiness behind the roasted barley that you wouldn’t have in say an Irish Dry Stout, toasted bread and toffee. Otherwise it’s clean without much identifiable character from the yeast or hops.
Taste – Starts out malty and rounded, distinctly Scottish to me. The finish is long and blends caramel and coffee, lingering and evolving for a few seconds after each sip. It isn’t a rich black coffee, more a Frappuccino - mellow and inviting, but not especially complex in terms of roast. Hop bitterness is low, but it doesn’t come across overly sweet thanks to the roasted barley and toasted oak.
Mouthfeel – The carbonation is perfect, very light, nothing to disrupt the body. Sadly the body itself is underwhelming. Not thin or watery by any means, but not substantial enough for the flavors.
Drinkability & Notes – Perfect beer to drink on a snow day. Loads of flavor, without too much alcohol. Begs for another sip each time. Maybe next time I’ll add 10-15% flaked oats or rye to enhance the body. Otherwise, just about there!