Grinder - Eureka Specialita
Beans - ONA Raspberry Candy roasted 8 days ago
Recipe: 18g in and ~37g out
Machine - Breville Barista Express - no OPV mod, but I'm holding the 2-cup button until I reach my output so that the brew pressure is not gajillion bar.
Holding the button allows me to have the gauge needle sits in the middle which equates to ~9 bar for my grind setting (from what I understand reading from various sources on the world wide web)
Might be wrong, but doing this way, my shot got so much nicer, not harsh, even with my unsophisticated palate I could taste the berries and white chocolate as what they say on the bean bag - so I reckon the internet is right 😅

Anyways! Video below, shot is pouring okay - but towards the end, there was a "bubble" in the middle - why do you think it's like that?
Pulled few more times - sometimes the "bubble" is smaller, sometimes not there at all (or I didn't notice)
Taste is fine in all of them - so just curious about this "bubble" 🤔