Alpha Acids in Hops: Why the Number on the Bag Matters
If you have ever brewed the same recipe twice and the bitterness came out a little different, you are not imagining it. One of the most common reasons is the alpha acid percentage on your hops.
What are alpha acids
Alpha acids are the compounds in hops that turn into bitterness when you boil them. That is why hop packages show a percentage like 6.2% or 12.8%. In general, higher percent means more bitterness potential.
Why that percentage changes
Hops are an agricultural product, so they naturally vary from crop to crop and lot to lot. Weather, growing conditions, harvest timing, and processing can all shift the alpha acid percentage from one year to the next. Even within the same hop variety, the alpha acid number on the bag can be different.
A real world example with German noble hops
This shows up clearly with Hallertau Mittelfrüh. Depending on crop year and lot, published industry ranges commonly span from about 2.3 to 6.6% alpha acids. In recent years, some German crops have also come in lower than many brewers were used to, especially after extreme growing seasons. For example, the 2022 crop year in parts of Germany was reported as very dry and warm, with acid values reaching record lows and alpha acid yields hit particularly hard. So it is not unusual to see retail lots of Hallertau Mittelfrüh sitting around the mid 3 percent range, like a 2024 lot listed at 3.5 percent.
Why it matters for recipe consistency
Most of your beer bitterness comes from boil additions, especially longer boil additions like 60 minutes. If your recipe was built around a hop lot with a different alpha acid percentage than the hops you have today, using the same hop weight can change the beer’s bitterness. That is why two batches can taste slightly different even when everything else is the same.
The easy solution: Use Brewfather or similar software to match IBUs
You do not need to do any manual calculations. Brewfather is a free brewing app that will do the IBU recalculations for you. The key is simply entering the alpha acid percentage from the bag you are actually using.
How to adjust hops in Brewfather (our preferred brewing software)
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Open your recipe in Brewfather
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Click the hop addition you are using
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Enter the alpha acid percentage printed on your hop package
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Brewfather will automatically recalculate the IBUs for that addition and your total recipe
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If you want to match your original target bitterness, adjust the hop weight until the total IBUs are where you want them
A couple quick tips
Start with your main bittering addition first. That is where alpha acid differences usually matter most.
Late hops and dry hops are mainly about flavor and aroma, so small alpha changes there are usually less noticeable.
Need a hand dialing it in?
If you want your beer to taste the same batch after batch, bring your recipe and your hop alpha acid numbers into TrueBrü and we can help you match your target IBUs in Brewfather fast.