The first big stout I brewed at Jackie O’s (Athens, Ohio) was Dark Apparition in 2007. Back then, a beer finishing above 6° Plato (1.024) was considered pretty thick!
Initially my approach to building body and depth of mouthfeel was to incorporate a large variety and percentage of specialty malts. A large amount of darker crystal malts, chocolate malt, aromatic malt, and some oats would provide complex sugars that would not ferment and remain in the finished beer. Maxing out the mash tun and hitting a higher mash temperature, 154–156°F (68–69°C), were also standard techniques used at Jackie O’s in the early days. The mash-specific techniques created a beer that commonly finished around 5.5–6.5°P (1.022–1.026). As styles evolved and palates changed, the bigger beers needed a boost.
The brewing team at Jackie O’s moved toward a more concentrated mash and a longer boil and increased the addition of adjunct sugars during the boil. These new techniques took the starting gravity higher than 26°P (1.110), and we started seeing FGs closer to 8–10°P (1.032–1.040). The idea was that the yeast would slow down, unable to consume all that sugar. From there, the gravities got higher, yields got lower, and mouthfeel became more and more dextrinous. At times, we used maltodextrin and lactose to provide more residual sugar in the finished beer, but that was more recipe-specific than a technique that we used across all big beers.