pH & Finished Beer

[manticle]

There's all sorts of chemistry going on in a mash that resists pH changes.

 

[Mardoo]

Also, different sensory thresholds for different people. I once shifted the pH 0.4 points with an acidulated malt addition at 4% of the grain bill. For the first three weeks after ferment I kept tasting sour flavours in the beer, but my mate couldn't taste it at all. Then the flavour faded. Once I revisited the recipe I realised that it may have been the acidulated malt I was tasting. When I took it out, no more sour flavour, but my mate had never tasted it. Not all tongues are the same.

 

[Jack of all biers]

4mL in a keg containing ~15L.

That is a lot. Are you sure your finished beer pH is 4.4 after that addition?

No more than what I hear some people add to the mash though, I guess the flavour is more prominent when adding post fermentation?

That maybe true, but adding to what size mash volume? To counteract what alkalinity? Even using Adelaide tap water, my last sparge water was at pH 7.1 and 3 ml 90% Phosphoric and took it to pH 4.76 (that last addition of 0.5ml got me again). That was 37L sparge water. I know that is like comparing apples to grapefruit, but point is, I'd be concerned adding 4 ml of 88% lactic (or any acid for that matter) to 15 L of beer. That is extreme and no wonder it left it apparently sour.

I think the whole point of the different research, all points back to ensuring that the all things are taken care off along the way of a brew. It's a whole package thing, that when you get to the point of having to add acid to the final product, then you have failed somewhere further up the chain. Ensuring quality ingredients (including water), attention to mash criteria (temp/pH/grist/water ratio etc), attention to yeast viability and vitality, attention to fermentation temps and on and on...

Point is, it is definitely worth knowing how things affect other things along the way and how to fix up mistakes as you go, but adding 4ml of lactic acid to 15 L of beer, should be causing alarm bells. The kind that say, don't do it, don't do it....

 

[mtb]

I should correct myself - 2mL in 15L of 4.8. Resulting pH is 4.55, which is nowhere near the reduction you saw @Jack of all biers, so I'm not too sure where that's gone wrong. The bottle is labelled 88% so it's not a concentration thing. You also definitely have a point re failing further up the chain - this is my attempt to correct pH in an already finished brew. I now take pH readings throughout the mash to nip the problem in the bud.

Moving forward, I've gotten myself a 1L bottle of 85% Phosphoric. I'll run some test batches to dial in the required additions and see how I go from there.

 

[Jack of all biers]

My example wasn't a good comparison, hence the apples and grapefruit comment. Your beer and my water would have vastly different buffering capacity, but the volume comparison was what I was highlighting, so sorry for the bad comparison.

 

[Jrrj]

I don't think I came back with the results of my experimentation with phosphoric.

My notes from a few weeks ago - feel free to point out where I went wrong with my back of the envelope calculations!

- 11 August I took a pH sample and it measured high 4.7s. I added 2ml of a 1/800 dilution of 85% phosphoric acid to 80ml beer sample, then this tested pH 4.05. This would imply that 19lt/.08lt x 2ml = 475ml will give the same result in a whole keg. To reduce that slightly, 400ml of the dilution could be tried in the whole batch, which is the same as 0.5ml of pure 85% phosphoric acid in the batch. To avoid spoiling the batch, I propose to add 0.2ml then test pH, then 0.2ml again then test pH, then a further 0.1ml at a time if additional pH reductions are desired. Following that, I will take final gravity measure, carbonate and then serve.
- 15 August I progressively added approximately 5ml of 85% phosphoric to approximately 18 litres of uncarbed beer that had measured pH 4.7 previously (0.5ml, then 0.5ml, then 1ml, then 2ml, then 1ml, shaking the keg and letting it settle for a couple of minutes between each sample, which was taken through the liquid post from a beer gun). Post addition pH test scored 4.36. These results suggest conclusions from the previous testing had been invalid (ie the assumption that 0.5ml would move the batch from 4.7s to 4.1s. Perhaps the 1/800 sample jar was mislabelled or miscalculated and should have been 1/80 dilution? Or had otherwise changed?).​

Since my earlier posts on this thread I also went back and re-read what Gordon Strong says on the subject in Brewing Better Beer. The main conclusion I drew from that was to adjust my brewing water to pH 5.5 with phosphoric, and to include Magnesium Sulfate in my salt additions (6g Calcium Sulfate, 2g Calcium Chloride, 2g Magnesium Sulfate added to 40lt of water). I'm hopeful that this will solve my problem of high pH throughout the brewing process.

 

[Lyrebird_Cycles]

I should correct myself - 2mL in 15L of 4.8. Resulting pH is 4.55, which is nowhere near the reduction you saw @Jack of all biers, so I'm not too sure where that's gone wrong.

88% Lactic is near enough to 12M (molar) and monoprotic so you have 12 m moles H+ per ml if fully dissociated. The pKa is 3.86 so at beer pH it is not fully dissociated; your 2 ml should represent about 20 m moles H+.

The buffering capacity of beer is generally around 90 m moles H+ / [ pH x kg extract] or 12 mmoles H+ / [pH x litre] at around 13 oP. I would therefore expect you to move 15 litres of wort by about 0.1 pH unit with this addition.

Note: edited to correct error in density of lactic solution

 

[mtb]

88% Lactic is near enough to 10M (molar) and monoprotic so you have 10 m moles H+ per ml if fully dissociated. The pKa is 3.86 so at beer pH it is not fully dissociated; your 2 ml should represent about 15 m moles H+.

The buffering capacity of beer is generally around 90 m moles H+ / [ pH x kg extract] or 12 mmoles H+ / [pH x litre] at around 13 oP. I would therefore expect you to move a little less than 0.1 pH unit with this addition.

As always your input is appreciated LC. Last night Bru'n Water and a newly acquired 1L bottle of 85% Phosphoric helped me to achieve a great mash pH and subsequent on-point pH levels. The proof will be in the final product though, I re-brewed a previous lager that ended up at 4.8 post fermentation and tasted.. "muddy". This time around I hope for a much better result.

 

[Lyrebird_Cycles]

- 15 August I progressively added approximately 5ml of 85% phosphoric to approximately 18 litres of uncarbed beer that had measured pH 4.7 previously (0.5ml, then 0.5ml, then 1ml, then 2ml, then 1ml, shaking the keg and letting it settle for a couple of minutes between each sample, which was taken through the liquid post from a beer gun). Post addition pH test scored 4.36.​

​

5 ml of 85% phosphoric contains about 7 g of acid, MW is about 100 so that's 70 m moles. Phosphoric is effectively monoprotic at beer pH* so that's 70 m moles H+.

Using the metric given above, that should move your beer pH by about 0.33 pH units, very close to what you report.

Did you by any chance do the 1/800 dilution by weight? If so that introduces an error of about 70%: 85% phosphoric has a density about 1.69 g/ml.

* The pKa for the second and third dissociation are each well above beer pH so they don't come into play.