Hops Lose Alpha Acids in Storage (Part 3 of 3)

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A spreadsheet (Apple Pages) used to calculate alpha acid loss over time.

In the previous post, I related a quick and dirty way to estimate the loss in alpha acids of hops over time, assuming they were stored in a freezer. That method was based on two measured variables (initial alpha acid percentage and amount left after 6 months at 68 °F/20 °C), plus a couple “guesstimations” — how the rate of loss changed at colder temperatures and a linear extrapolation from the initial condition through the one “data” point.

We would expect the loss of alpha acids to be an exponential function. So, it’s almost certain the simple model underestimates hop losses prior to six months and overestimates them after 6 months — although the deviations should be small. Using the simple method is better than not accounting for the losses at all, but there is a more accurate way of estimating the alpha acids if you’re willing to put in a little more work. [Read more…]

Hops Lose Alpha Acids In Storage (Part 2 of 3)

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Alpha acid loss in two hop varieties over time, estimated from data from Hop Union. (In reality, the rate of loss is likely not linear. See the next article for more details.)

As I detailed in the first half of this article, hop alpha acids levels decline during storage. Proper handling can slow the degradation of the alpha acids, but even properly stored hops gradually lose their bitterness over time. In this post, we’ll examine if the loss if alpha acids is great enough to matter, and how to account for it if you do wish to take it into consideration. [Read more…]

Hops Lose Alpha Acids Over Time (Part 1 of 3)

HopBagAlphaLet’s say you buy an ounce of Cascade hops and it says 6.0% alpha acids on the package. What is the percentage of alpha acids in your hops? This might seem like a trick question, but it isn’t. Alpha acids decay over time and the percentage listed on the package represents the level when the hops were analyzed. The number may be substantially lower when you brew with them. In each hemisphere, hops are harvested once a year. Once harvested, the clock is ticking on their alpha acid levels. For advanced homebrewers — especially those brewing hoppy beers in the few months leading up to the next hop harvest — it pays to understand what is going on and how you can adjust for it.

The major variables contributing to the decline in alpha acid levels are temperature, exposure to oxygen, exposure to light, and the variety of hops. As a homebrewer, you should store your hops in a way that minimizes their degradation.

[Read more…]