R/O water - 4.8 pH (?)

[eye-of-ra]

I'm getting ready to brew my first AG batch. I'm using Bru'N water to calculate my water chemistry. I thought I had it pretty well figured out until I tested the pH of my R/O water. It registered as 4.8. My first question is, does that sound probable? Second, when I was familarizing myself with Bru'N, I was using the starting pH of 8 and everything made sense. When I plugged in 4.8, I was still being instructed to add some acid (Lactic, in my case) to the mash. Again, does that sound probable?

Here is my grain bill:
American 2-row 6 lb 6.6 oz
Wheat 3lb 5 oz
Flaked wheat 10.9 oz
Carapils 10.2 oz
Rice hulls 9.4 oz


Thanks

 

[day_trippr]

Yes, it's plausible, I've seen the same from my RO system.

Yes, acid is still needed, because the ph of the base water doesn't mean much when the same water has nearly zero buffering ability to shift the mash one way or the other...

Cheers!

 

[eye-of-ra]

Thanks for the confirmation! I'm brewing a Blood Orange Wit that is really popular in the summer and didn't want to mess it up.

Cheers!!

 

[acidrain]

The PH of the water means nothing. If you've been reading up, then you know that it is the mash PH that matters.
Most of the good on-line water profile spread sheets are right at the predicted mash PH when building from RO water.

 

[FVillatoro]

As the other forum members state, mash PH at room temperature is what matters. The malt will act as a buffer and the PH will increase after you dough in.
When I was started doing water additions, I added lactic acid to my water and the PH was 3.9. Once I mashed in it came in at about 5.3.