Low yield mozzarella ( only 300gr of cheese per 4L of milk )

[tunnn]

I made several batches of mozzarella according to Gavin's recipi and they all succesfull. But i just realized i get ony 400gr of curd ( drained ) and 300gr of cheese ( stretched ) per more than 4L of milk :'( :'(.
Please help me, what do i do wrong. I also add calcium chlorine, i bought raw Hoistein milk from local farm.
I kept curd at 40 dergees C until pH reach 5.2. Maybe the only worst thing is my rennet took 15 days shipping to me but it seem to be fine. The coagulation occurs in 45min.

[Aris]

You might have over worked the mozzarella curd making it lose moisture and butterfat. I've made a lot of Mozzarella and I only stretch it slightly and lightly knead it until smooth. I only use water buffalo milk nowadays and the yield I get is over 19% (4 liters milk = over 760 g of Mozzarella). 

[tunnn]

You might have over worked the mozzarella curd making it lose moisture and butterfat. I've made a lot of Mozzarella and I only stretch it slightly and lightly knead it until smooth. I only use water buffalo milk nowadays and the yield I get is over 19% (4 liters milk = over 760 g of Mozzarella).

thank you for your suggestion.
Well, my first and second batches that i made faild because it dropped pH so quickly so i didn't work on it. And i still only got ~300gr curd.

[tunnn]

here my stretched mozz image: https://photos.app.goo.gl/X7Sg4JBad2WUGGaVA

[Aris]

It looks dry, I bet it is also rubbery. The video below shows good technique on how to form a Mozzarella.
https://youtu.be/Jw_ah-WRrBE?t=1015

[tunnn]

Update
Finally, my mozz got 14% yield thank to another milk supplier. Maybe the milk form the first supplier is low in protein and solid due to grass feed (as they said).the freshly grass flavor of that milk is amazing but not worth 8 hours