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I've always disagreed with the idea that dry hopping or late hopping added 0 IBUs to your end product. If I ever brewed a kit or recipe and followed the hop schedule exactly, it would pretty much always end up too bitter. I found out that my local water PH was high (8.0) when running into some astringency issues and wondered if that had anything to do with it. At first I thought it was the high sulfate content in my water so I did the following tests. What I ended up finding is that lower PH (more acidic water) lessened the perceived bitterness in various hop tea tests.

Two-water hop tea test

8 oz local tap water heated to 160F with 1 hop pellet CTZ (in PPM Ca=45,Mg=15,Na=65,SO4=125,Cl=50,HCO3=225)

8 oz distilled water heated to 160F with 1 hop pellet

Stirred and after 15 minutes examined. I noticed that with the tap water the hops didn't precipitate as much and clumped at the top. The local tap water produced a much more back-of-the tongue bitterness. I had two others test in a blind taste test and they all grimaced when they tasted the tap water hop tea. The aroma was similar if not more pronounced with the distilled water.

This led me to my next test, trying a cold hop test to mimic dry hopping.

8oz local tap water (see above) with 5 hop pellets CTZ, crushed and stirred. Sat 40F for 12 hours. 8oz distilled water with 5 hop pellets, crushed and stirred. 40F for 12 hours.

My results were similar to the hot hop tea experiment. The distilled water dry hop tea yeilded a much less bitter result while the local tap water dry hop tea was very bitter and harsh.

I thought I had figured it all out, there was some correlation with either high sulfate or HCO3 content but I wanted to see if PH was the determining factor instead of mineral content. I had read that high mineral content accentuated hop bitterness (famously so in Burton water) but in my quest to trying brew a really nice IPA with great aroma and low perceived bitterness.

8oz local tap water (see above) with 5 hop pellets CTZ, crushed and stirred. Sat 40F for 12 hours. 8oz local tap water with 10 drops lemon juice, 5 hop pellets, crushed and stirred. 40F for 12 hours. No PH readings taken (broken ph meter)

To my surprise there was a big difference, it was very obvious that there was less bitterness with the acidic sample. Also on the high PH sample, the hops clumped at the top and left a clearer liquid. I couldn't notice a difference in aroma.

Can someone replicate this? Maybe someone with a good PH meter?

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Bitter is a flavor that detects basicity. Adding acidity to bitter flavors typically converts them to salts, though the salts here would not be metal salts and probably not salty in flavor. Even if the acidity helped dissolve more of the bitter hop alkaloids, they would probably not increase the bitterness for this reason. However, this is just speculation and not a real answer (thus the comment). I haven't done the experiment. I've just seen it a number of other plant extractions in ethnobotanic studies. I personally like bitter flavors and wouldn't test removing. –  ex0du5 May 28 '13 at 4:30
    
I also like the bitter flavors when it balances aroma. The bigger picture to this experiment is to maximize hop aroma while keeping bitterness in check. The big IPAs out there touting hundred+ IBUs but when you drink them they're fairly tame in bitterness. Sure, the IBU scale is flawed but I think additions at flameout and dry hopping should not be counted as 0 IBU (that's what Beersmith's IBU calc does). But based on what you're saying it's common knowledge that bitterness and PH have some relationship so that's encouraging. –  user3484 May 31 '13 at 2:35

2 Answers 2

This study demonstrated that iso-alpha acids degraded more quickly in low pH environments, particularly at lower temperatures. If I'm understanding this correctly, I think this means that lower pH beers will lose bitterness over time, compared to high pH.

Perhaps your experiments are showing the same effect. The high pH samples were more bitter because the iso-alpha acids in the low pH samples had degraded more.

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Reading a little about humulone isomerisation, it seems that both Ca2+ and Mg2+ ions catalyse the reaction, while aqueous alkali is also mentioned (see e.g. Table 8.2 in However, Brewing: Science and Practice by Chris A. Boulton and Peter A. Brookes).

All three are present in your tap water but not in the distilled. I would conclude that the bitterness you observed was indeed due to some isomerisation occurring in the tap water.

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