I just updated BeerSmith and decided to try out the new pH features. I normally use Bru'n water so I decided i'd compare the results of both programs and make sure they match up. As you might imagine by now, they did not match up at all.
I wouldn't expect them to.
First, Bru'n water works great when I'm brewing 7bbls, its spot on every single time, ...
You have some problem with your pH measurement technique. It is impossible for any calculator to be 'spot on' (which I am interpreting as meaning ±0.02 pH) because you can't measure pH that repeatably with a real pH meter using buffers with ±0.02 pH tolerance (the tolerance of the NIST traceable operational buffers that most of us use. Even if we used, in the brewery, the techniques we use in the lab to get ±0.02 accuray none of the popular programs (neither of the ones mentioned here) have the ability to accept the required malt characteristics to allow a pH prediction that accurate. It is doable but the calculator must know the DI mash pH, at least one and more probably (depending on the malt) 2 titration curve parameters and the malts temperature glide. The programs you are referring to use malt type and color as proxies for these because no one has the full parameter set. Attempts to get the maltsters to measure them have been fruitless. Malt color isn't a bad proxy but it isn't a particularly good one either.
So how is it that lots of people report "Well I don't know how you are screwing up but Sudsawater is spot on for me every time". I don't know but I strongly suspect it is confirmation bias. You want the program to be accurate and so you dip your pH meter and watch the numbers. The pH of a mash varies quite a bit over time and thus if you wait long enough you will get to the number you expect at which time you declare victory and write down the predicted number in you logbook even though perhaps if you had waited longer the pH would have continued to drift. This doesn't always work out, of course, and when it doesn't confirmation bias protects you by making this aberration less memorable than measurements that confirm your expectations. Confirmation bias is very real and powerful. Talk to one of your friends or relatives that thinks either of the current presidential candidates is fit for the office.
...but when I brew a 8 gallon batch, my mash pH always comes in too high. I've corrected this by shooting for a mash pH of 5.2 if I want 5.4.
This makes no sense so again I expect a problem with pH measurement or the interpretation of the reading. It would be worthwhile to compare the two meters (I'm guessing that you don't use the same one at home as at work but perhaps you do) and running the stability check (see Sticky at the top of this forum). There may be a very small difference in acheiveable pH for exactly the same proportions of exactly the same malts with exactly the same water but I would guess that none of those factors is indeed exactly the same. Things tend to be more stable in a larger system as the ratio of thermal mass of the mash to the vessel surface are is larger and so that might be a factor.
Now, when I set up my water profile in BeerSmith and it calculates my 88% lactic acid addition, its saying i need 7.3ml to get it down to 5.4, whereas bru'n water tells me to get down to 5.2 pH (usually gets me 5.4) i need to add 4ml.
Each of the two programs comes up with a mash pH prediction using the descriptive data you feed it on malt type and color but they use that data in different ways neither of which is, AFAIK, analytically robust by which I mean that I believer there is a lot of empiricism mixed in. In any case the models are not the same and thus the predicted pH's are different.
Anyone else have similar issues, or perhaps an explanation for what might be causing this discrepancy?
Lots of brewers have noted these discrepancies. If you want better pH predictions lean on you malt supplier to give you the data you need on the products he sells you. Given that data it is actually quite simple to calculate a good pH estimate.
