What's so ironic about the Scottish Heavy Ale? Mostly that it's not exactly what you'd call heavy - it's actually one of the lighter beers you'll find, at least in terms of gravity. Everything is relative, though, so it's worth noting that there are differences between this style and its close relative, the Scottish Light Ale.
While the Heavy may not be heavy in comparison to…well, almost anything else, it is heavier than the sixty-shilling light ales of Scotland. To the extent that we care about differences between beers and how those beers are produced, that's really all that matters!
But Scottish Heavy is definitely a style that requires a deft hand, and nailing the "heavier" but still "Scottish session ale" elements is important. There's more to this beer than taking your Scottish Light recipe and adding a few more gravity points.
There are essentially three "weights" of standard Scottish ales (the Wee Heavy or Strong Scotch Ale is so far beyond these that it shouldn't even be spoken of in the same breath): Light, Heavy, and Export (sometimes known as 60 shilling, 70 shilling, and 80 shilling, respectively, for the rate at which they were traditionally taxed). The Light is the lightest, of course, and is designed to "overperform" in flavor terms given its (sometimes almost-non-alcoholic) gravity level.
The Export starts to resemble the ESB or American Pale Ale in strength and intensity. The Heavy, though, lands in the middle of the range, and it can be hard to make one that stands out if your approach is just "make it a little stronger." All three bear similar hallmarks of Scottish ale flavors: caramel, biscuit, and minimal hops.
The question is this: how much flavor are you aiming for? At the judging table, we're looking for something with more apparent bulk and flavor than the Light, but we still want to be able to see some restraint. It can be a hard needle to thread, which makes this even more ironic: the Scottish Heavy might be the easiest of the three to make.
Parts of this recipe stay the same. Our base grist is still mostly Maris Otter (six pounds/2.7kg) and Munich (one pound/0.45kg), and the half-pound (0.23kg) of British 65L crystal stays the same. That base and crystal lay down some solid caramel, bready, and toasty flavors. However, I leave out the Victory and higher-lovibond crystal malts here - we don't need to "fake" body and flavor quite as much, given the extra gravity we get to play with. Instead, I sub in another half-pound each of chocolate rye for the pale chocolate (to add some spicy malt flavors along with the touch of drying roast) and some malted wheat for a smooth breadiness. The result is a rich-but-drinkable malt profile with an ABV of about 4.3 percent, which is actually a touch high for the guidelines, but isn't uncommon in the marketplace.
Hopping is still restrained - this is, after all, Scotland - and 20 IBUs of anything at all in the 60-minute addition will be fine. You can add a small addition (a quarter-ounce or 7-8 grams) of East Kent Goldings or Fuggles at the end of the boil for a bit of floral, earthy British hops character, but it's an accent at most.
And I stick with the Irish Ale yeast on this one (Wyeast 1084) for the same malt-friendly effects we're looking for in the Scottish Light Ale. If you prefer to use a traditional Scottish yeast, feel free - for that matter, I've had some fun results with Northern English yeasts that are a bit ester-crazy, too, but you might end up with a fun beer that doesn't match the style parameters!
So, why do I say this beer is the easiest of the three to make? Because we're dropping out the kettle caramelization completely and mashing at our usual temperature (152F/67C for me). The crystal and chocolate malts we're using will provide enough residual, unfermentable sugars, and there's no particular need to add the bit of flavor and color development that kettle caramelization would impart.
Mash and boil and chill as usual, and pitch your yeast into a nice, cool wort. 63F/17C is a great fermentation temperature here, and will produce a clean and malty near-session-strength ale in about 7-10 days. Don't worry about a diacetyl rest: a little diacetyl is a good thing here. One major departure for me is that I like to carbonate to about two volumes of CO2, which is higher than cask/pub versions of the style, but I think it brings out the aromas nicely and improves the mouthfeel, making it more substantial.
The higher carbonation level is a drag on the Light, which has more-delicate malt flavors, but the Heavy can handle it and, I think, benefits from it.
Don't think of Scottish Heavy as just a higher-gravity version of the same recipe, made distinct only by how much it's taxed. You can, but you're missing out on the opportunity to make a distinctly worthwhile beer! What do tax collectors know about beer, anyway?