It's time to test out the validity of another of Drew's favorite techniques - keg purging.
Breweries spend a lot of time worrying over removing as much oxygen possible from their packages (bottles/kegs). Why? It's pretty well established both in tradition and science that oxygen is destructive to beer flavor and aroma pretty quickly. So packaging brewers do everything they can to reduce O2 levels after their intial injection of oxygen post chilling.
On the homebrew side, we tend to be a bit more cavalier. We have the protection of knowing who's going to be handling our beer post packaging and we're fairly certain that person isn't going to do idiotic things like leave the beer out in the sun, etc. For the most part at least.
How far can careful O2 handling and storage take you? It can nab you Ninkasi awards. Jamil Zainasheff talked about winning medals with lower gravity beers that were over two years old. They still tasted fresh because of the care he took while bottling and the subsequent cold storage he kept them at. Drew's experience included a keg of his Gnome Is In The Details - a light weight Belgian blonde ale designed to express the Wyeast Ardennes yeast. He brewed it and served it at the first San Diego Homebrewer's Conference in 2011. The keg went into the deep freeze to be ignored because things and when it came time to get ready for the 2014 Conference in San Diego, there it was - still fresh as it had been 3 years prior. Drew claims it's because of the cold storage and his purging technique.
Drew's technique is fairly straightforward. Fill the keg (to the top, brimming) with your sanitizer. Push the sanitizer out with CO2 (preferably into another keg) and then fill the keg with your fresh beer. Chill, carbonate and store. The idea being that the CO2 will completely replace the liquid with minimal remaining oxygen.
The more popular technique with homebrewers involves multiple (~7) cycles of filling the keg with CO2 and then releasing the pressure. The operating principle says that doing this will cause CO2 to settle in the keg and displace the O2. Since O2 and CO2 are miscible, the multiple cycles are needed to repeatedly decrease the amount of O2 left behind.
So which is better? Let's do a couple of experiments to find out:
1) Package with no purging / Package with Drew's Total Purge
2) Package with Cycled Purging / Drew's Total Purge
All the kegs will be stored cold. (Cold vs. warm storage is another test)
Since hops fade more quickly - the tests will be done using a hoppy recipe. We'll be using an open top transfer to allow IGORs who aren't capable of pressure transferring to participate.
Brewing Sessions Needed:
- Sanitize 2-3 kegs (2 for only one leg, 3 if you're testing all 3 purge styles)
- For the no purge keg, do no purge. Gently rack the beer in via the top covered with foil.
- For the cycle purge keg, purge by completely filling the keg with CO2 at 25 psi. When filled, pull the pressure relief valve and completely bleed the pressure. Repeat 7 times. Gently rack the beer in via the top covered with foil.
- For the full purge keg, fill the keg with sanitizer and push it out with CO2. Gently rack the beer in via the top covered with foil.
- Note any color changes (post testing). The oxidized beer can appear darker
- Any other aroma changes?
- Brew enough volume of the target recipe to split the wort into two-three equal fermenters. Chill and prep the wort/fermenters exactly the same
- Ferment the batches in the same space and under the same conditions, especially temperature. Match the fermenters and other equipment.
- After fermentation subsides, record the length of fermentation and the final gravities.
- Package the two beers in kegs. One keg should be purged via Drew's method, the other not purged at all or cycle purged as decribed above. (If doing all three, prep all 3 styles of purge) Chill and force carbonate. Store cold. Wait one month before testing.
- Perform a triangle test with samples of the full purged vs cycle/no purge and record the results. If doing all 3, please make sure to do two separate tests, but always with one of the test beers being the full purge.
- Ask the testers for their observations on the samples. DO NOT Reveal the Difference between the samples.
- If creating all three styles of purge. Give your tasters, post triangle test, samples of all three and have them rank the beers.
- Discuss the results and record any further observations.