What volume is the acid adjustment applied to?

[brian_muz]

Hi,

I've been having trouble with overshooting my Ph fairly significantly. I've been added my acid addition to the mash tun. I was just thinking that my salt water additional are for "mash" water and "sparge" water and mash water included my mash out addition. Is the acid the same? In other words have I been adding my acid addition to the mash water only when it was meant to adjust both the mash and mash out total volume?

Thanks for your help.

[Oginme]

Without seeing the amounts and additions, I cannot respond accurately.  The acid addition recommendations in BeerSmith are based upon adjusting the mash pH and not the overall pH of the resultant wort.  Given this, it would seem that the answer may be that it is based upon the volume in the mash infusion as the mash out addition and sparge are after the fact.  Also check the sticky note on this forum topic http://www.beersmith.com/forum/index.php/topic,20449.0.html which gives some feedback on the pH prediction model that is used in the software. 

[brian_muz]

Here is an example from a recent brew. You can see I planned to mash in with 17L and then add 11L to mash out.

It took me a while with BS3 to work out that mash salt additions are applied to the combined volume (28L).

I added a 2ml addition of 85% phosphoric acid which BS3 says will make the adjusted Ph 5.45. I didn't make it enough to drop to what I really wanted (5.2) as I always overshoot.

I was thinking through this and I was wondering if BS3 assumes my acid will be added to the combined volume (28L) or what I've been doing and adding it to the mash tun which is only 17L. If Its built on the premise that this is added to the 28L then that would explain why I'm overshooting my reduction by so much.

Thanks for the link to the prior thread. This is useful too.

[Oginme]

I think you are working too hard at this.  The relevant lines from Mark's comments are below:

"Here is the bottom line on the errors in acid additions: equation (6) in my second paper (... Mash pH II...) appears to overestimate the buffering capacity of a typical grist. Hence, the amount of acid required to hit a target pH is overestimated."

"Consistent with your (and others) observations, recent preliminary analysis (of actual mash pH measurements) by me indicates the buffering capacity is overestimated by a factor of about 1.65."

So if you take the acid recommendations from BeerSmith and divide that value by 1.65 you will get a lot closer to your target pH.   It has nothing to do with the volumes and everything to do with a flaw in the model.

[BOB357]

I changed the 88% lactic acid entry to 135% and no longer need to do adjustments for every mash.

[brian_muz]

@oginme I get where you are coming from and I understand that the formula seems to be out but as I work towards getting this better than where I currently am I'd say that there is a big difference between addition 2ml of acid to 17L and adding 2ml of acid to 28L. There is going to be almost 33% more acid by volume in on compared to the other. The software must be designed to dilute the acid addition by one of these volumes. I'm just asking which one.

@Bob357 cool hack. Once I work this out I'll give it a go!

[Oginme]

So, go back to my original response:  "The acid addition recommendations in BeerSmith are based upon adjusting the mash pH and not the overall pH of the resultant wort." 

This means that it is targeting the pH of the mash which includes the grains and water used for the mash steps.  Mash out is not a mash step but a process to cease the enzymatic process and is not included in the calculation for mash pH.  Sparge water is intended to rinse the sugars from the grains and is not included in the calculationof mash pH.