Brunwater calculator work best for me.
Work by dilution, ie to lower acidicity,( higher pH values) step by step
Do by making 350 ml then dilute to 3500 ml(target)
Sanity check:
Rinse ph meter with water when pH readings is doubtful.
Measure again with tap water, and calibration liquids
From brun water excel calculator,
For target pH5.6, 4 L final volume
Using 6% phosphoric acid
Need 2.6 ml of acid.
From experience, initial 350ml is around pH 2.5 or 2.6
When making 3500 as final volume, start by add 80% to 85% of calculated water amount, ie 2800 ml in this case
Add the required salts, eg gypsum and calcium chloride before adding more water. Stir to make sure all is dissolved
Add 50ml every time to watch how pH values go up ( less acidic)
PH starts ~ 4.6 to 4.8
Every 50 to 100 ml lower acidicity by ~0.1(pH values go up 0.1)
The trend is not linear,but increase in steps
I think ph 5.4 or 5.5 is good enough. My cheap pH meter can have a deviation of 0.2 or maybe more.
Double check with ph paper when reaching ~5.0
Tips
Constant stirring
Read after 15 seconds
Cleanse the pH meter tip when in doubt
Jot down the values in a chart can help visualise
Final mash water is 3400ml instead of 3500 ml. It doesn't really matter, as you can increase the malt amount accordingly.
When you gain more experience, you can start from 90% target volume, and bigger steps
Noticed that in another trial, pH values increase suddenly from 5.7 to 6.4 in one step. TBC.
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