Sudden Drop in Sparge PH

[nman13]

Yesterday I brewed my all-grain saison and it was the first time I messed with mash and sparge PH (up until now ive been using DC tap water that has a PH of about 7.2.)

After some research, I determined that I should get my Sparge Water to a PH of 5.7 before sparging. I began to add about 2ml at a time of 25% Phosphoric acid to my heated 4 gallons of sparge water. Each addition had the PH drop a small and consistent amount until it reached 5.9. I then added another 2ml and the next reading I took dropped significantly to 3.7!!!

Does this make sense? Could my PH meter be broken? Or is PH adjustment in water not linear?

I did this exact same thing to another 2 gallons of water that I had and the same result happened. I tasted both samples and they tasted just like water (no sourness at all.)

I also put my meter back in the 7.0 buffer each time to recalibrate and each time it was really spot on and there was no need to calibrate which leads me to believe that the meter was taking an accurate reading.

Any ideas or help?

 

[GotPushrods]

Or is PH adjustment in water not linear?

It is not. Google the term "titration curve" to see some examples. This is completely normal.

 

[nman13]

Ok. Thats what i figured. I batch sparged first 2 gallons of7.2 water (way to high) and then second with 1 gallons of 3.7 water (way to low)

will the second acidic batch sarge cause significant issues with the beer?

 

[pvault98]

Also, it is advised to add your acid to the sparge water before heating, not after. The reason is it is assumed you calculate how much acid you need based on the initial mineral content of your water, but as you heat the temporary hardness is removed thus changing the alkalinity of the water. If you add the the predetermined amount of acid at that point, you will likely over-acidify.

In your instance this does not appear the case since it sounds like you did not do any calculations before hand. In addition to the non-linear nature that has already been discussed I would also throw out that it can take up to about 15 minutes for the PH to stabilize after adding acid and it is necessary to thoroughly stir after adding so that you are not testing an area that the acid hasn't been incorporated into or vice versa.

I would definitely suggest knowing the mineral composition of your water and starting Ph and then calculate the amount of acid needed rather than just guessing with each addition or you will find yourself bouncing all over the place trying to get there.

 

[mabrungard]

You only need to add acid to water before heating if you have calculated the quantity of acid needed based on the room temperature alkalinity of that water. If you have measured the alkalinity of your pre-heated water and calculate your acid addition based on that reduced alkalinity value, then it's fine to add acid to hot water. If you are just adding acid drop by drop and measuring pH, then its also fine to add acid to hot water since their is no calculation involved.

By the way, the quick drop of the pH with that final drop is typical. The pH drop was consistent in the early part of the acid addition. That is the range where there was still alkalinity in the water. Then you finally exhausted the alkalinity and the pH drops like a brick. That is farther than you wanted to go.