Double IPA

Double (or imperial) is a term in the beer world for a stronger and more intense version of a familiar style. It is not a sum.

The figures show it. According to the BJCP, an American IPA has 5.5–7.5% alcohol and a double IPA 7.5–10.0%. The Brewers Association uses 6.3–7.5% against 7.6–10.6%. A double IPA therefore has clearly more alcohol, but not twice as much. The BJCP calls it bigger in alcohol, bitterness and hoppiness, with a comparable balance to the regular American IPA.

There is a kernel of truth in it, though, when it comes to the hops. Brewer Vinnie Cilurzo wrote that for his first double IPA, in 1994, he took the recipe of what would become his IPA and 'literally' doubled the hops. He increased the malt by some 30%, not by 100%. The style guides do not prescribe a fixed amount of hops.

You come across both 'double IPA' and 'imperial IPA', and abbreviations such as DIPA or IIPA. Those are not different styles.

The BJCP calls the style Double IPA (22A) and adds itself: 'Rarely called Imperial IPA.' The Brewers Association uses both names at once: 'American-Style Imperial or Double India Pale Ale'. Untappd also puts them together in one sub-style: 'IPA - Imperial / Double'. And when the Great American Beer Festival opened a category for these beers in 2003, according to Acitelli, it was called 'Imperial or Double India Pale Ale'.

Which name a brewer chooses therefore says nothing about how the beer tastes. That also goes for the cloudy version: the Brewers Association calls it 'Juicy or Hazy Imperial or Double India Pale Ale'.

In master's research at Oregon State University (Barnette, 2018), dry-hopped beer was stored cool (3 °C) and warm (30 °C), with different amounts of dissolved oxygen. The storage temperature had the biggest effect on the aroma. With heat and more oxygen, tropical, citrus and hoppy aromas disappeared, and malty, dried-fruit and cardboard aromas took their place. Oxygen had a smaller, but demonstrable effect after just two weeks.

Other research, from the VLB in Berlin (2022) on eleven commercial hoppy ales, shows that it is more nuanced. Some hop aroma compounds stayed reasonably stable, other aroma compounds (esters) less so, and compounds that go with ageing increased.

The Brewers Association writes of the double IPA that the beer must show 'the fresh character of hops', without oxidised or aged flavours.

So store IPA cool and drink it fresh.

IBU (International Bitterness Units) is, according to CraftBeer.com, a measure of the bitter compounds in beer, determined in the lab as milligrams of iso-alpha acids (converted bitter compounds from hops) per litre. The Brewers Association writes in its style guidelines that this figure measures one specific hop compound and does not consistently match how bitter someone perceives the beer. It gives three reasons for that: sensitivity to bitterness differs per person (partly through genetic make-up), other ingredients also contribute to bitterness, and hop aroma and flavour can strongly change the perceived bitterness.

The guidelines themselves give examples. For Export-Style Stout the BA writes that the bitterness can turn out high in the lab, but that the sweetness of the malt dampens the perception. Conversely the BJCP says of kölsch that drier versions can seem hoppier or more bitter than the IBU suggests. And in hazy IPA the bitterness is, according to the BJCP, often masked by the fuller body and the soft finish.

For orientation: CraftBeer.com gives 5–10 IBU for light lagers and 50–70 for robust, bitter IPAs. So use IBU as a rough indication, not as a flavour promise.