Aged Hops

In light of the lambic that we are making next I have been doing some research into what I need to do to make it as authentic as possible. One of the things that is traditionally done with lambics is to use aged hops. This might sound a little strange because it goes against the traditional handling of hops, but there is a method to the madness. Basically the idea is to age the hops so that the acids have broken down to produce no bittering components. This is partially because lambics are not supposed to have hop flavors, but the primary reason is for preservation. There are too primary things in beer that preserve them, one is alcohol, but the other is hops. It turns out that traditional lambic isn’t very alcoholic at all. The BJCP style calls for original gravity between 1.040 - 1.054 sg and 5-6.5% ABV, so the hops are important for preservation.

This got me thinking about how I was going to find hops with low enough acid to get some preservation qualities from them without imparting hop bitterness or flavor. I did a little googling and came across a 2004 article from brewing techniques that focused on how to preserve your hops. More importantly it provided equations on how to fairly accurately calculate acid loss over time. So I figured I would try to calculate if any of the hops I had lost enough acid to be used. I did order 3 lbs over a year ago and still have some left.

In the end it turns out that I-2 years in cold storage in a vacuum sealed container really only drops around 2% acid, which is not enough to make a difference on anything but Saaz. So that doesn’t help. So instead I will probably just get some Saaz now, stick it in a paper bag in a warm room and maybe in 30 days or so the hops will lose 1% of acid. Saaz is only 2.5% to begin with, so it should be the best option.

The formula used to calculate the acid loss is shown to the right (FA = ...). It is comprised of six variables, two of which should be readily known (A and D), and one that we are calculating (FA). The other three (K, TF, SF) have there own derivations depending on some other factors. I will describe these three below:

• Rate Constant (K): this constant represents the rate at which your hops lose their acid. Over time hop brokers developed an index called the Hop Stability Index (HSI) which reflects how much acid is lost in six months if stored at 20° C (68° F). Typically this information is presented in the form of a % loss by hop suppliers. In fact if you go to hopunion and check out there variety guide you will see this defined under storage ability. You can also calculate the % lost using the HSI if you have that instead. To calculate K, you need to use values for the original acid value (Ao) and final acid value after 180 days (An). Obviously, you won’t have either, but you can calculate the original acid value, and use a arbitrary value for the final acid value because the calculation is a ratio. The equations for calculate this are to the right. 
• Temperature Factor (TF): this represents the affect temperature has on the storage. It is expressed as an exponential decay function, starting from 1 halves itself every 15 °C (27° F). So for example if you stored the hops at 68°F the TF would be 1.0, at 41°F - 0.5, at 14°F – 0.25. The equation for this is again in the image to the right.
• Storage Factor (SF): this represents the affect the storage container has on the aging. 1.0 for “Not sealed or sealed in poly bags”, 0.75 for “sealed in barrier packaging or airtight jars, but not free of oxygen”, 0.50 for vacuum sealed. That last value seems to be calculated by the auther using experiments.

Have have just summarized the equation specifics. There is more information in the posting. I have also created a Excel spreadsheet that does some of the calculation for you.