Please help me troubleshoot my Mozzarella - no process detail spared!...

[Cheese curious]

Hi,

Apologies if anyone already saw this on Reddit, I'm hoping for some more tips so reposting here.  Several posters here have already helped me a lot in reaching this point and will probably recognise some steps in my process!... Any tips gratefully received.

I've arrived at the following process. The resulting Mozz is usually at least slightly rubbery, It's ok fresh but not great. On Neapolitan pizza (my main use) it's pretty good but it stops being stretchy maybe 2/3 of the way through eating a pizza, and I'm a fast eater of pizza.... not sure if this is a single issue (stopping stretching too soon is related to the rubberyness), two separate issues, or, indeed, if this is normal and I should stop fussing.

Kit:
- big stainless steel pot in an Igloo of water with a sous vide immersion heater in it
- digital probe ph meter and thermometer
- vacuum packer
- colander & cheese cloth


Ingredients/process:
- 9L of whole milk pasteurised but not homogenised.
- Take one ~750ml jug of it, heat to 98F, add thermophilic culture and maintain at 98F
- start heating the rest of the 9L in the pot (sous vide warming the water outside it to 98F). 1/3 tsp 33% CaCl mixed in some distilled water and added.
- When at temp, add the jug of starter culture, stir in, leave at 98F until ph 6.3
- Add 1.7ml microbial rennet mixed in some distilled water. Stir well up/down for 20s then leave until flocculation point (this is about 12 minutes)
- At 3x floc, cut curd into 2", leave to heal for 15 mins then cut to 1/2" and leave to heal for 5 mins
- Gradually heat sous vide to 102F over 45 mins, gently stirring every 5 mins or so and breaking any matted or bigger curd chunks spotted
- At ph 6 drain curds then leave in colander/cloth at 98F until ph 5.35
- Then put into a few vac pack bags (not vacuumed yet) and put in fridge.
- When cold, drain then vacuum, store in fridge or freezer depending how soon needed.
- When needed, gradually warm to room temp then keep going until 98F or ph 5.0 (whichever is soonest)
- Stretch test at ph 5.0 - if it's an easy and almost indefinite stretch then chop into roughly 1/4" x 1/4" x 2" sticks, put in bowl and add ~120F water
- After a few minutes, drain to just below the top of the curds, add some salt then ~165F water
- bring together and gently align/stretch (as little as possible). When soft and smooth start rolling it up, pinching off balls.
- Sit balls in ~90F water with some salt and CaCL in it for 20-25 mins. Then remove and wrap in cling film.

My inkling is that the issue may lie in the stretching process but I'm really not sure - so many variables! - so I thought I'd spare no detail. Many thanks for any pointers.

[Cheese curious]

Quick PS question:

I made a batch of curd today and the ph level went down really fast after cutting.  If I drained them at 6 ph as planned then it would have been just a few minutes after cutting & healing, before they had a chance to warm up to 102F.

I decided to let them heat for a bit then drained at 5.8 ph - wasn't sure whether the ph or the heating was more important to the result so thought this would be hedging my bets.

Grateful if someone can explain the purpose of the heating and also why we should drain at 6 ph?

Then I guess next time adding the rennet a bit sooner, like 6.4 ph, would be the way to reduce risk of this happening again?

Thanks for any advice.