Bubbling in coffee

[Banananananana]

Hi there! First time posting here. I'm having this recurring issue with bubbles in my coffee. I haven't changed my techniques and usually my milk had no bubbles and is silky. I've noticed some bubbles in the espresso and have tried swirling it before pouring, but the bubbles appear really quickly.

The bubbling does not occur when I pour with super flat under aerated milk.

Did an experiment with different milk temperatures but it's still occuring.

Ive never encountered this problem as frequently when I worked in a different place with different beans but same milk brand. The beans I use are not really fresh. Usually they're 2-3 weeks old after roasting. Could the problem lie with the roasting? Or am I really doing something wrong.

We're brewing the coffee at 96.5degree celcius (as per roaster's suggestion)
Espresso is a blend from guatemala and brazil
steam wand pressure 1.15bars (la marzocco gb5)

need all the help I can help! Thank you!!

 

[Seb]

If you could still try an other brand of milk just to confirm if it comes from the milk of the coffee that would help. I have seen this problem few times and usually it is related to the milk. But it could be just the period of the year....i mean the cows alimentation may vary between summer month to winter and recently i had this problem for few weeks using the same milk brand i use since many years. Then, i change the milk brand and it was ok so i knew it was related to the milk. But recently i went back to the previous milk brand as i prefer it and no problem now. That is strange and hard to diagnose sometime.

What you could do is steam the milk, be sure it is perfectly silky smooth texture immediately after the steaming. Let it sit for 1min but swirl it from time to time to avoid the fat to separate. And take a close look to the surface, if it's the milk it will start bubbling while resting (which was my case). If not, then it's the coffee and usually this is related to too fresh coffee but 2-3 weeks should be perfect. Except maybe if it is very light roasted as it take more time to release the Co2. Again to try to isolate this....grind the coffee in your PF but let it sit 10min before tamping it. This way if the problem is Co2 release from the coffee you will know it.

If you have the bubbles immediately following the steaming, then it is related to the espresso machine (pressure, steam tips) or steaming pitcher or barista technique.