Bubbles arise in foam

(Kate Seward) #1

I recently opened a cafe, and we’re struggling with our foam bubbling shortly after pouring a drink.

We’re working on a 2-group, la Marzocco Linea. We will start with perfect milk with glossy micro-foam, and pour beautiful latte art, just to find it start to bubble even before a customer receives their beverage.

Sugars do seem to help stabilize it a bit better, so our mochas will hold well.

I’ve tested multiple types of (dairy) milks, steam wand tips, steam pressure, and am struggling to get to the bottom of this. I am wondering if it is the acidity in our espresso? We are currently using a Guatemala/washed Ethiopia that is a light to medium roast.

Has anyone experienced this before, or does anyone know of some research available that talks about this?


(Ben Cordova) #2

Hi Kate, we are using the same machine and I have to believe its your coffee. Im sure its great but what else could it be. If your are steaming great micro foam and pouring latte art then its not the milk? Does it happen in ceramic AND paper?

(Ben Cordova) #3

What are your grams in and grams out and brew time?

(Kate Seward) #5

Thanks for the response Ben. What is your steam pressure set at? Yes, it’s ceramic and paper, and our ESP ratios are currently at 1:1.5 and 1:2 .

(Wesley Griffin) #6

I find that if you can finish foaming milk before the milk temperature reaches body temperature then the foam is more stable for longer, holding it’s glossiness and maintaining latte art. If you’re getting a nice, glossy micro-foam I’d keep foaming the milk how you’re currently doing it, but try to finish foaming before the temperature of the pitcher feels “neutral” (not hotter than your hand, not cooler). After that point just get a good roll/whirlpool going to integrate the foam into the rest of the milk well. I find that foam introduced after body temperature doesn’t hold well and ends up bubbling pretty shortly after pouring the drink.

I find that does the trick for me. Not sure if it’s totally scientific, but I haven’t found any other solutions to that problem.

(Kate Seward) #7

Thanks for the response Wesley. We’ve only been having this problem at our new cafe which is using new espresso and new equipment, so I’m assuming it’s something to do with one of those??? I haven’t run into this before in my career, so it’s is really boggling my mind. I’ll definitely keep an eye on stretching too late in the game though- thank you!

Kate Seward
Form & Function
Coffee // Roasting // Supply


511 W Broad St. Boise, ID 83702

Find us on Instagram and Facebook

(Shawn Thacker) #8

…this is the thing that has improved my milk texture more than anything else. I used to try to increase the volume too much by aerating for too long when steaming. Introducing air early and then dipping below the surface to ‘swirl’ is a great tip here! :+1:


(Ben Harker) #9

We had a similar issue when we opened and sometimes still do. With our initial coffee roast/roaster, the acidity seemed quite high. I noticed that this problem only used to appear in the darker parts of the foam (once poured and swirled) and then progressed to the light sections. however it never happened in the white milk foam art sections. I did some testing (not scientific) by making some milk and letting it stand in a glass and in a glass on hot water and the issue never arose. we also never saw it with hot chocolate or chai. We have since changed to a different coffee and this issue now only arises on some coffees if I have not got the dial in exactly right. This seemed to indicate that the acidity was having an exaggerated effect on milk froth that was less than perfect, and even then.

(Kate Seward) #10

Ben, thanks so much for your response. It sounds like you know exactly what I’m referring to. Yes, that is accurate that the bubbles do not form in the white sections of the pour, which also lead me to believe it had to do with the espresso and milk combining.

When dialing in your new coffees, how do you adjust the grind/roast/extraction to find a working solution? Thanks again for your time and understanding!

Kate Seward
Form & Function
Coffee // Roasting // Supply


511 W Broad St. Boise, ID 83702

Find us on Instagram and Facebook

(Ben Harker) #11

Hi Kate, I’m relatively new to coffee from a barista point of view. With our first coffee is to adjust the acidity by taste from the espresso shot. this was difficult as I am still trying to develop my pallet to understand what the coffee is telling me. So I kept to the constraints that seemed most important, and that was the dose/yield. I did some research on extraction time and just moved within the accepted boundaries (20sec - 28ish) based on what I could read and watch. I just then kept looking at what was happening with the bean through day and observing when the issues seem to get worse. I never did get it to stop with the first coffee we had. I have since changed roaster and this issue has not been as prevalent. I have noticed that the if it happens its usually only when the crema gets darker. this indicates that I have let the grind slop some. I also find that getting the milk to mix with the coffee crema during the pour process, I have far less trouble. This is for me still not completely conquered but is far less common now. I have only been at this about 10 month though.

As for the nitty gritty of my process, I dose 22g for 35-40g yield (my machine varies a bit) and I currently time for 25sec. this seems to have a nice balance with the blend I have and keeps enough punch in the coffee. It also allows me just enough time for the 60g yield used in my 12oz. what I have worked on most is distribution within the filter basket. I use 25g VST baskets to get enough head room for the 22g dose. I use the tap method to even out the dose in the basket before using the O.C.D V2 to even out the top. I have a Pullman 58.5 (VST Matched) tamper to help tamp as evenly and close to the basket edge as possible. This things have have made a difference as the last of the espresso seems to indicate a more even extraction that just smashing the dose down from what ever pile the grinder gave me ( this was how we started :man_facepalming:t2:). I do however get a bit OCD myself with the timing and dose, as I keep things to within .8g and 2sec from my target throughout the day.

Sorry if this was a bit long winded… and I would be very interested in advice other may have on this as well.


(Troy) #12

Another potential factor is the very small grind particles that find themselves in the crema, which affect foam stability. The amount of fine particles is affected by the beans, the roast, the grind setting, the temperature…
There are some good articles in the scientific literature on the subject: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3140933/

(Kate Seward) #13

Rad. Thanks for that Troy. I’ll definitely dig into that literature!

Kate Seward
Form & Function
Coffee // Roasting // Supply


511 W Broad St. Boise, ID 83702

Find us on Instagram and Facebook

(Stevie Hutton) #14

My two cents:

It’s like the milk quality and freshness. I’ve worked with a number of milks and found the fullest fat, unhomogenised milk works the best and settles a lot better than stuff available at the supermarket.

Secondly, before pouring latte art, i add about 20ml of steamed milk into the espresso and give it a good swirl and a mix - which creates a good base to pour into, and it has been adequately emulsified to ‘sit around’ for a little longer.

(Kate Seward) #15

Thanks Stevie. I have started to swirl some milk in with the crema as well, seems to help sometimes! We use whole milk for our milk based drinks. I’ll definitely check out the milks that we’ve tested to see if they’re all homogenized. I’ve found it’s nearly impossible to figure out how fresh the milk actually is. How do you purchase your milk and keep tabs on freshness?

(Stevie Hutton) #16

Buy it direct from a decent dairy and use it within 2 days. We get deliveries every other day. We also use white cap (a little richer than blue). General rule of thumb not to go through a middleman or wholesaler. In your case, try and find out where the good places local to you get their milk from, and just use them.

(Abdulmohsin) #17

Sometimes the bubbles accrued due to the freshness of the coffee beans. Freshly roasted coffee beans have lots of gas and you need to let them rest/degassing.

(Kate Seward) #18

Thanks for you response! We let our espresso rest 7-10 days. From what I’ve read that should be sufficient. Have you had any issues like this with coffee that it 7-days off roast?

(David Greco) #19

I know that someone mentioned it above and you said 1.5 - 2.0 on your brew ratios. I have found some coffees to hold up to the milk better at different brew ratios. Typically darker roasts at closer to a 1:1 - 1.5 but it’s a also a taste thing as well. I’m curious though if that affects things much for you since the brew ratio is going to say a lot about the TDS in the coffee which could contribute to the break down of the foam. Assuming that milk is good, which it sounds like it is. I doubt it’s the machine, no doubt there is a learning curve with any new machine but it’s the least likely culprit in my opinion based on your description.

(Kate Seward) #20

Thanks for your response! Yeah, I am wondering if it’s the acidity in the lighter roasted coffee. Definitely something to dig into more.