Many kettle sour brewers are lowering the pH of the wort to 4.5 prior to pitching souring bacteria in a effort to maintain head retention in the finished beer. The challenge is knowing how much acid (usually lactic) to add in order to achieve the desired pH. One such brewer is using EZ water by inputting a mash pH of 4.5 and noting the amount of acid required. Then he inputs his desired mash pH (say 5.4). He then adjusts his mash water using the latter and after sparging adds the remainder of the former calculation. Is this a feasible way to get the finished wort in the pH 4.5 ballpark? If not, is there anyway to predict the amount of acid to bring wort to that level?
Can wort pH be calculated/predicted?
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You need to know the buffering capacity of the wort just as you need to know the buffering capacity of mash to predict mash pH or the amount of acid required to change pH by a given amount. To determine this titrate the wort with acid. Take a liter or a quart or a pint or whatever is handy and add lactic acid from a syringe until desired pH is reached. Now scale the acid by the total amount of wort to be treated and add it the whole volume.
You can WAG the amount of acid required by assuming wort buffering is about half of mash (based on kg of malt used in the mash).
You can WAG the amount of acid required by assuming wort buffering is about half of mash (based on kg of malt used in the mash).
In my experience, wort buffering is fairly consistent over the typical range we deal with in mashing (5 to 6 pH). Extrapolating beyond that range could be iffy. However, I have the feeling that making that extrapolation with Bru'n Water would present you with a reasonable approximation of what your acid dose would need to be to drop the wort pH to 4.5.
Thanks, guys. I used this thread as a reference on our wiki (and thanks Mark for starting this conversation): http://www.milkthefunk.com/wiki/Sour_Worting#How_to_Pre-Acidify
Thanks A.J and Martin. Come see us over on Milk the Funk (facebook group). We are all about alternative brewing yeast and bacteria. We have several microbiologist in the group but no water experts. We also have the wiki Dan mentioned above that perhaps has became the main go-to source for commercial and home sour and funky brewers.
Sorry for the bump, but is there any reason you couldn't put the probe in the wort while gently stirring and adding the acid a few drops at a time until 4.5 is reached? The wort will be cooled to around 110F, so I don't think that will damage the pH probe.
When you do this you are measuring the buffering (alkalinity) of the wort and this is exactly the way you should go about this. Remove a sample of the wort and cool it to room temperature. Add lactic acid to the target pH (keeping in mind the shift with temperature) then scale the amount of acid you find to the full volume to be acidified and add it. If you look in a German brewing text such as Kunze you will see that this is exactly the procedure he spells out.
Ah. I see that this is exactly what I suggested in #2.
Sorry if I wasn't clear. I meant stick the probe in the full volume of the wort, stir gently while adding a drop of lactic at a time and monitoring the pH until it reaches the target.
No, you were clear. I am just suggesting that you do the titration on a small volume of cooled wort in order to save stress on your pH electrode. It is then trivial to extend the titration result to the full volume.
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