Bru'n water

[cunnol]

Messing around with Bru'n water and I've entered my PH as 7.5.
When I go to the estimated mash PH its already down to 5.6 without me entering any water adjustments or KGs of grain.
Anybody know why this is?

[Slev]

Is it set to use existing water or adjusted water i  the grain bill section

[cunnol]

I tried both and the PH still stayed at 5.6

I downloaded the excel sheet off their website again and its the same. I'm very confused altogether.

[Slev]

Was curious afterwards.  Played around with it and did see what you are talking about.
Noticed that gat the starting water ph,  didn't affect mash ph.  The mineral make up did. 
So after a bit of googling,  i came across this discussion on hbt

http://www.homebrewtalk.com/showthread.php?t=538506

[Slev]

Basically (and i could have this horribly wrong) :
Starting ph is of little concern,  as its the buffering which is of concern. 
M.  Brun said that he only uses the initial inputed ph to calculate the carbonates and bicarbonates on the first page.  Hense why it appears to differ from the grain page ph  (which is not anyway valid until a grain has been entered)

[cunnol]

Cheers Slev, that makes sense, this post explained it best for me:

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The effect of the water is tiny. The grist contains orders of magnitudes more molecules affecting the pH than the small masses of various ions and dissolved solids in the water.

Think about it. Mineral additions to RO water are in the order of grams for 5-10 gallon batches. A typical grist for a a 5.5 gallon batch at 1.050 will be ~9.25 lbs in my setup.

Lets assume 10g of mass present in 8 gallons of strike/sparge water using tap or RO water with additions. That is an overly large estimate

The same mash will contain ~4000g of grist

That's a 400x difference in mass in water and the grist. I would surmise the effects on the water pH will be of a similar differing magnitude.

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I used Bru'n water before to calculate the amount of gypsum to add to a light pale ale mash. Ended up with absolutely zero hop flavour compared to the previous no addition batch. Gonna presume it was another factor that contributed to that. Got some lactic acid and a salifert kit on the way to help me out, definitely lacking punch from my hops with the water from vartry