pH of just-done HP soap.

[Garden Gives Me Joy]

If anyone has ever measured the pH of HP soap immediately after cooking it, what pH did you observe please?

Does the pH immediately lower after you add superfat?

Have you ever noticed if the extent by which the pH lowered (assuming it did) correlates with the percentage of superfat?

 

[ResolvableOwl]

Post-cook superfat is fat/oil. It is water-insoluble and pH inactive by itself. There is just no way that it can change the pH value of a solution.
(Exception: stearic acid for cream/shave soap)

Besides this, pH is known to be unreliable and at times even deceptive.
https://classicbells.com/soap/pH.asp
NB: The pH of soap is dependent on recipe. Even if someone gives you a pH reading from a freshly done HP cook, it is useless unless you're using the same oils.

XY reply:
A pH test could at best tell you if there is excess lye or not. It cannot help you to decide if HP is finished.
The easiest and most reliable way of telling when to stop cooking, is the clarity test. If there is any lye left (negative superfat due to measurement inaccuracy, SAP uncertainty, or on purpose), it is the whole point of PCSF to care about it during cure.

 

[Zany_in_CO]

If anyone has ever measured the pH of HP soap immediately after cooking it, what pH did you observe please?

In addition to @DeeAnna 's Soapy Stuff and what @ResolvableOwl explained above, there really is no reason to pH test CP or HP lye-based soap (pH 9-10) unless you suspect it may be lye-heavy (pH 11-14).

Kenna of Modern Soapmaking covers how to do it correctly here:

How to pH test Handmade Soap

 

[Garden Gives Me Joy]

My interest in asking about pH after book wsa not due to an interest in knowing when to stop cooking. Rather, I was just interested in the pH to know whether the soap really has the same pH, at least more or less that it will always have. For instance, does it start with pH 10 or 10.5 ... or start at about 9 or 9.5.

Yes, indeed re unique recipes rendering different pH values. However, I am more interest in general trends.

Eta: I want to experiment with pH sensitive additives and wondering whether their addition is possible immediately after HP cook, super fat or re-batching.

 

[Zany_in_CO]

I was just interested in the pH to know whether the soap really has the same pH, at least more or less that it will always have.

In general, lye-based soap that starts at pH 10 - 10.5, generally gets milder, pH 9.5 - 10 after cure.