Citrusy, resiny, and bitter, the American Imperial IPA is an aggressive beer—and a rich one. This style grew out of the demand for hoppier beers at the start of the American craft beer revolution. As IPAs were brewed with more and more hops, the amount of grain needed to balance out the bitterness increased. The results were IPAs that were so extreme, with over 8.5% ABV and 100 IBUs, that they took on the moniker Imperial, which was previously reserved for only the biggest stouts.
Ten years ago only a handful of examples could be found, and almost exclusively on the West coast. Today breweries all across the country join the pioneers like Russian River's Pliny the Elder, Stone's Ruination, and Rogue's I2PA in making this homage to the American hop.
For homebrewers, brewing an Imperial IPA can be a great challenge. The high alcohol content means you have to pay close attention during fermentation, and the large quantity of hops makes the brewday a lot of fun. The extra ingredients are also usually enough to push the cost of the beer to almost twice what you would normally spend on a homebrew recipe. When I make an Imperial IPA I expect to spend between $40 and $60 for a 5 gallon batch.
The grain bill for an Imperial IPA is very similar to the grain for an IPA, it's just bigger. Even though many people call it a 'double' IPA, the amount of grain is more like 1.5 times as much. So while a typical IPA might use 11 pounds of grain for 5 gallons, an Imperial IPA will use about 17 pounds. Standard American 2-row should be used for 85% to 90% of the total grain bill. The remainder of the grain is used to add complexity, so Munich, victory and crystal malts work quite well. If you want a heavier IPA that really coats the inside of the mouth, then half a pound of crystal 120L and some Munich malt really does the trick. If you're looking for an Imperial IPA with a more crisp, assertive hop character then a mix of 40L crystal, carapils, and corn sugar should comprise 10% to 15% of the grist.
You want a lot of high alpha acid, high citrus hops for an Imperial IPA. Columbus, Centennial, Chinook and Cascade are the usual suspects, and most Imperial IPAs have some blend of them throughout the process. Many of the most popular commercial Imperial IPAs also have generous helpings of Simcoe hops to get that pine character in it. For a 5-gallon Imperial IPA, you should be using 1 to 2 ounces of high alpha acid hops at the beginning of the boil, 1 to 2 ounces in the middle of the boil and 4 to 5 ounces in the last 15 minutes of the boil. This type of schedule will give you high IBUs and a lot of hop flavors.
Dry hopping is also essential for this style. I recommend 4 to 6 ounces of dry hops, left in the beer for 5 to 7 days. Don't leave that many hops in the beer for longer than a week, otherwise unpleasant vegetal flavors could develop.
When you use this many hops, you should expect your beer yield to decrease substantially. A lot of liquid gets tied up both in the kettle hops and in the dry hops. It's the price you pay to get that extreme flavor, so it's something you just have to live with. I expect to lose just under 1 gallon of beer for every 5 gallon batch when I'm making an Imperial IPA
Yeast and Fermentation
With such a big beer, fermentation control is very important. If you already have good fermentation practices, you should be fine. It's essential to use lots of oxygen, lots of yeast, and keep your temperatures down, otherwise you'll be getting off flavors developing during fermentation.
For an Imperial IPA I like to err slightly on the side of too much yeast, so I'll make about a 4 liter liquid yeast starter or use 1.5 packages of dry yeast. Even if you typically use liquid yeast, it might be worth making this beer with dry yeast, because it offers much better control over the amount of yeast in your pitch.
The varieties of yeast used for this style are usually either an American Ale yeast or an English yeast. The English yeasts usually bring out more crisp and dry flavors, while the American yeasts give a more rounded flavor that melds the hop and malt characteristics.
Take a look at our recipe for an Imperial IPA. This recipe is based on Avery Brewing Company's Maharaja, and it makes a fantastic homebrew Imperial IPA.