Phosphoric acid becoming more acidic????

[Braufessor]

Hey - Question about phosphoric acid.

I always have used lactic acid for my mash/sparge. I have read that phosphoric is more flavor neutral. To be honest, it is probably irrelevant as I am not using high levels of lactic acid...... always .75ml/gallon or less. But, none the less, I decided I would try some phosphoric acid I had sitting around just to see what I thought.

I ended up using about 4ml/gallon of phosphoric to aim for my desired mash pH of 5.45. I was using B'run Water to calculate. The phosphoric acid was 10%.

Long story short - my mash pH was 5.18. I NEVER miss my mash pH by more than a couple hundreths using lactic acid/B'run Water calculations. I tried to compensate by adding some high bicarbonate water to my boil kettle and boiling longer. Got my pre boil pH to around 5.3 or so.

At any rate...... I am mainly just curious at this point. Can phosphoric acid become more acidic with time. It was an old bottle I had laying around. 2012...... It did look like there was probably some evaporation - which would account for some change I would think. Although, it was not like half the bottle was gone or anything.

I did take a pH reading of the phosphoric acid itself and it came in around .86 - not sure what the pH of 10% phosphoric would normally be.

I suppose it could have been mislabeled too maybe. Brewer error of some sort is always a solid possibility as well.

At any rate, just kind of wondering about the possible reasons I would have undershot my pH by so much in using phosphoric acid compared to lactic acid that I normally use.

(pH meter is accurate and was calibrated before and after use to make sure. Other readings in batches before and after were right in line with normal and with B'run Water projections)

 

[ajdelange]

88% lactic acid is 11.4 N to pH 5.4 while 10% phosphoric is 1.09 N to that pH so you would need 7 mL of the later to be equivalent to 0.75 mL of the former. Something doesn't compute here.

 

[Braufessor]

88% lactic acid is 11.4 N to pH 5.4 while 10% phosphoric is 1.09 N to that pH so you would need 7 mL of the later to be equivalent to 0.75 mL of the former. Something doesn't compute here.

The .75ml of lactic acid per gallon is the MOST I ever really use. This particular recipe would have been less lactic acid than .75ml/gallon. My guess off the top of my head is that if I would have used lactic acid in this particular recipe (scottish 70) to get to mash pH of around 5.4 it only would have taken about .3 ml/gallon to do it.


There was obviously (I think anyway) something not right about the phosphoric acid I was using..... It was driving pH way lower than it should have if it was 10% phosphoric acid.