A Craft Beer & Brewing Magazine reader recently asked us the following question:
I live in Colorado and brew at high altitude. Is it true that altitude can affect my hopping rate?
As altitude increases, the boiling point of water decreases. The practical effect of this is that your boil-hops additions boil at a lower temperature, which results in lower hops utilization. So at altitude, you may actually need more hops to achieve a given bitterness than a brewer at sea level.
So how much reduction in hops utilization do you get at altitude? My friend John Palmer recently wrote an article on the subject (“A look at Isomerization Reduction due to Altitude,” MBAA, Vol. 54, No. 3, 2017). He covers the subject in some detail, but I summarize his findings here.
The first question is how does the boiling point change with altitude? At sea level, water boils at 212°F (100°C). However, the boil temperature drops about 6°F (3.2°C) for every 3,200 feet (1,000 m) of altitude. I’ve put the actual numbers in Table 1, but we are looking at a boil temperature of 200.3°F (93.5°C) at 6,560 feet (2,000 m) of altitude, which might be typical for someone in the Colorado foothills. This is almost a 12°F (5°C) drop in boil temperature.
Source: “A look at isomerization reduction due to altitude.” Technical Quarterly, Vol. 54, No. 3, Master Brewers Association of the Americas.
So how much does this drop in temperature affect hops utilization? The alpha acids in hops go through a process called isomerization in the boil where they are converted to isomerized alpha acids, which provide the bulk of the bitterness in beer. This isomerization process happens when you boil but also continues at lower temperatures, albeit at a slower rate. Even in the whirlpool or post-boil steep, isomerization continues to add some bitterness to the beer.
Fortunately, due to the recent popularity of whirlpool/steeped hopping, we now have good models for hops utilization versus temperature. Palmer uses two recent models from hops experts Mark Malowicki and Thomas Shellhammer to provide his estimates. If we consider boiling at sea level to be 100 percent, the utilization drops to 56 percent at 200°F (93°C). This is a significant drop, meaning that at 6,500 feet (2,000 m) of altitude, you need about 44 percent more hops than a brewer at sea level would use to achieve the same bitterness levels.
You can use Table 1 to adjust your hops utilization at altitude. Keep in mind that it is relative to sea level, so you will either need more hops when brewing at altitude or need to boil your hops longer to achieve a target bitterness level.
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