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Old 05-31-2012, 01:56 AM   #1
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Default How Important is Residual Alkalinity?

Bear with me, this is my first real scientific effort to control my brewing water chemistry. I didn't find an answer to this specific question on the site, but I might not have known all the proper terminology to do a good search.

Here's a bit of background:
I am going to brew an ESB and had downloaded the Bru'n Water spreadsheet (really awesome, I am very impressed!) and plugged in the information for this mash. I was able to match the London water profile pretty easily with a a bit of gypsum and calcium chloride added to my Chicago water, but the mash pH was higher than I wanted (5.8). I lowered the mash pH by adding a total of 5 mL of lactic acid. BUT... this lowers my residual alkalinity to +2, which is a bit low for an amber ale.

For brewing purposes, does RA serve any purpose beyond achieving the proper mash pH? In other words, when creating a water profile for a recipe, is RA really that important, or is it just a tool for determining what mash pH will be?

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Old 05-31-2012, 02:08 AM   #2
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It's a tool for comparing different water sources. Don't worry about whether your RA is "correct". The pH of the mash is what is important.

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Old 05-31-2012, 10:11 AM   #3
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There is not a 'correct' RA for a beer color. The RA values included in the Bru'n Water profiles are just starting points (best guesses) with regard to the alkalinity and resulting RA for beers in that color range. Always let the mash pH guide the brewer as to what alkalinity and RA their mashing water needs for a particular brew.

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Old 05-31-2012, 12:51 PM   #4
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Great, thanks for the really insightful responses! I had a feeling that RA wasn't critical as long as the mash pH worked out so thanks for the confirmation.

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Old 06-01-2012, 11:26 AM   #5
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RA was intended to be a rough indication of how much acid would be needed to bring a base malt only mash made with a particular water supply. If the RA of a water is high lots of acid will be needed (dark malt, sauermalz, sauergut, hydrochloric acid...). If RA is close to 0 then little. If RA negative then less or even none. Thus it's main use is in comparing water supplies and this can be done using the chart at http://www.pbase.com/agamid/image/57446374. One plots his water's alkalinity vs its effective hardness and sees immediately what the RA is and where the water stands relative to other waters plotted on the same chart or well know brewing cities' water supplies. Things get a bit out of hand when people start including the effects of malts and added acids in the RA calculation which can lead to erroneous thinking if not carefully applied. Fundamentally the concept is valid but it would be better if it were recognized that one is dealing with buffering capacities and that malts, acids, and water each have buffering capacities and titratatble acidities/alkalinities all of which must be considered. RA is the titratable alkalinity of the water as adjusted by the titratable acidity of the hydrogen ions released by base malt phosphate in the presence of a given amount of calcium. Make an assumption about the buffering capacity of base malt and you have a pH predictor.

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Old 06-07-2012, 09:14 AM   #6
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So if you can reliably adjust your pH in the mash would there be any reason to fool with your water's alkalinity?

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Old 06-07-2012, 11:40 AM   #7
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If you are adjusting mash pH, you are 'fooling' with alkalinity. Most brewing works best with low alkalinity water. Its when alkalinity isn't coordinated with the acidity of the grist, that mash pH suffers.

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Old 06-07-2012, 04:55 PM   #8
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I'm just wondering if there is any reason for people to try and replicate a city's alkalinity with salts if you're just going to be removing it in the mash anyway with little acid additions.

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Old 06-07-2012, 05:14 PM   #9
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No, replicating alkalinity values from a historic or regional water profile is not appropriate. The only thing that matters is coordinating the alkalinity of the mashing water with the acidity production of the mash.

Adding alkalinity to produce a certain water profile and then having to neutralize that alkalinity with an acid addition is counterproductive. Starting with a water with low mineralization and adding only the salts necessary for mash pH and flavor impacts is a good way to go. Alkalinity is added only as needed to produce a desirable mash pH.

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Old 06-07-2012, 05:34 PM   #10
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Quote:
Originally Posted by truebe View Post
I'm just wondering if there is any reason for people to try and replicate a city's alkalinity with salts if you're just going to be removing it in the mash anyway with little acid additions.
There are occasions when one might want to do this but they are few and far between. They usually relate to the desire to be authentic i.e. to start with water (and, presumably, to the extent possible, other raw materials) that are as close as possible to those used by a particular brewery to brew a particular beer using procedures as identical to what was done in the particular brewery as possible. In such a case you go to the considerable trouble to prepare a volume of water that has the same chemistry (it's usually possible to get within 1% for each ion's concentration) as the original water and then process it in the same way. If the processing involves neutralizing bicarbonate with acid then it is much easier to simply add salt(s) with anion concentration equivalent to the bicarbonate (e.g. if the alkalinity is 2 mEq/L and you use sulfuric acid you add 2 mEq/L sulfuric acid and wind up with 2 mEq/L sulfate).

It is also possible that some beer somewhere may have residual bicarbonate flavor as part of its profile. I am not aware of such a thing but I suppose it is possible.

Generally, trying to duplicate a city's profile is a losing proposition because
1. Many of the profiles are seriously in error.
2. You have no idea as to how the brewers using that water treated it if at all.
3. Synthesis almost always requires that chalk be dissolved with carbonic acid thus mimicing nature's way. This is a big PITA.
4. It is often possible that you can make a better [insert name of style here] than the brewers of [insert name of town associated with that style]. The good burghers of that town were stuck with the water they were stuck with. You can do anything you like starting with RO/DI.
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