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According to this question's answer, from Denny Conn,

You don't pretreat the water because it's the mash pH you're concerned with, not the water pH.

And this agrees with this article on the power of pH,

Malted barley contains phosphates, which are acidic buffers. Making a mash of grain mixed with water will cause the phosphate buffers to achieve a natural pH of around 5.6. Therefore, it does not matter what the initial pH of your brewing water is because the interaction between ions in water and buffering components of the malt will always change the water pH.

But in this Gose recipe by Gordon Strong

On brew day, prepare your ingredients; mill the grain, measure your hops, and prepare your water. This recipe uses reverse osmosis (RO) water. Add 1⁄4 tsp. 10% phosphoric acid per 5 gallons (19 L) of brewing water, or until water measures pH 5.5 at room temperature. Add 1 tsp. calcium chloride (CaCl2) to the mash.

According to this fast souring article,

After your saccharification rest is complete, reduce the pH of the wort to 4.5 by addition of food grade lactic or phosphoric acid.

So what I'm gathering from all this is that you treat your mash to be between 5.2 and 5.5 for the purpose of ensuring the mash converts efficiently, and you treat your wort, post mash, to make it more friendly to your lacto inoculation (although, this is not specifically in Gordon's recipe).

  1. Does this sound correct, and if so, is Gordon's recommendation to treat the water incorrect, or does it have to do with the RO water?
  2. For a sour, would you treat the wort pH post mash or post sparge? Or does it matter at that point?

If it matters, I am batch sparging.

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You are perfectly correct, the mash adjust to around 5.2 is for conversion efficiency and to assure that minimal tannins are extracted out of the grain husks (especially important in dark beers). The post-mash adjustment down to 4.5 is generally suggested in order to prevent bacteria other than lactobacillus from growing in your wort since especially enterobacter thrives in the same conditions as lactobacillus. There is excellent information about the processes in the MTF Wiki article on wort souring: http://www.milkthefunk.com/wiki/Wort_Souring

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    That's a very helpful link. I had come across it before, but kind of forgot about it. That's a very thorough and informative wiki. Thanks!
    – Wyrmwood
    Commented Aug 17, 2017 at 19:19

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