Frothing: Milk level keeps rising, even after wand is fully submerged???

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alexanders5700

#1: Post by alexanders5700 »

Hey guys!

So I've been loving my Profitec Pro 700 and Niche combo, making great lattes (to my taste) every morning.
My question is: does anyone have a similar experience, and/or know the science behind, the phenomenon of the milk level in the frothing pitcher continuing to rise, even after the steam wand is completely, and absolutely fully, submerged in the pitcher?
And I mean 100% submerged. Like the tip is 3 inches in (hehe), almost at the bottom of the pitcher.
Milk used:
Brand: Natrel
Type; 3.25% fat, Natrel protein plus

More details: So I'll be frothing, hiss hiss hiss, looking good. I'll watch the milk level rise while doing so, and when it gets to the level I want (maybe 10-15% rise, after 4-5 seconds), I'll fully submerged the tip/wand (up to 2-3 inches below the surface level of the (swirling) milk).
No more hiss hiss, very silent swirl.
Sometimes the milk just swirls and stays at whatever level it's at (which is great), but sometimes the milk level just keeps on rising...
Absolutely no change in pitcher angle (in any or the yaw, pitch, or roll axis), I just raise the pitcher's altitude, and in so doing, the tip/wand becomes submerged. If I see the milk level continue to rise, I'll raise the pitcher level up to 3 inches, so the tip/wand is almost touching the bottom of the pitcher, but to no avail, the milk level keeps rising no matter how deep the tip/wand is submerged.

I was under the impression that as the tip/wand is submerged, no more aid is introduced, and thus milk level should no longer rise, as no new air bubbles are created to expand the total volume of frothed milk.

It's weird. The subsequent frothed milk is usable, very tasty, but often too foamy for good latte art.
it happens maybe every 1/3 to 1/4 time.
I am also very meticulous in ensuring my procedure is standardized every time, so I cannot see myself as the variable responsible for this phenomenon.

Anyways, if anyone has any experience with this, let me know if you figured out what was happening (and maybe the science?), and how to fix it?

Extra note: the only possible thing I could think of, is that potentially, maybe, there are some large surface bubbles that get sucked down and incorporated into the milk during the tip-submerged-milk-swirling-phase.
So even though the tip is submerged, and no hiss hiss is happening, some extra air (from inside the surface bubbles) is being incorporated... maybe, just a thought (but I haven't noticed a correlation between the times when I had large surface bubbles at the beginning of the froth, and the times when the milk level kept rising after the tip/wand was submerged. Something for me to pay more attention to)
Cheers!

Smo

#2: Post by Smo »

The steam turns into water and remains in the milk. Weigh your milk before and after frothing.

User avatar
HB
Admin

#3: Post by HB »

I never really thought much an about it, but I've noted submerging the steam wand doesn't necessarily bring stretching to a dead stop. I've overflowed more than one pitcher post-submersion with a commercial espresso machine (e.g., 2 group Strada). I assume it has something to do with the speed of the roiling since that never happened on slower steamers (e.g., Breville Dual Boiler).
Dan Kehn

alexanders5700 (original poster)

#4: Post by alexanders5700 (original poster) »

The steam certainly does condense into water and add volume to the milk.

However, as I start with the same volume of milk every time, and the milk is the same temperature every time, and the boiler is at the same temperature every time, as is my home temperature, as is the temperature that I steam my milk to, the amount of water volume/mass introduced into the milk pitcher should be identical.

And thus should not be the difference factor between the times when the milk level keeps rising, and the times when the milk level does not rise (post submerging of the tip/wand).

ie, the amount of added water should be consistent from all experiences.

Unless of course there is a problem with the Profitec Pro 700, if it does add more water on some occasions vs other occasions, which should not be the case if the machine is performing properly.

Cheers

alexanders5700 (original poster)

#5: Post by alexanders5700 (original poster) »

HB wrote:I never really thought much an about it, but I've noted submerging the steam wand doesn't necessarily bring stretching to a dead stop. I've overflowed more than one pitcher post-submersion with a commercial espresso machine (e.g., 2 group Strada). I assume it has something to do with the speed of the roiling since that never happened on slower steamers (e.g., Breville Dual Boiler).
Sounds like a similar circumstance.
I wonder how the rolling, if that is the factor affecting milk level post submerging, affects the milk level...
Maybe a powerful roll can, in and of itself, introduce more air into the milk (even without the hiss hiss)?

alexanders5700 (original poster)

#6: Post by alexanders5700 (original poster) »

Smo wrote:The steam turns into water and remains in the milk. Weigh your milk before and after frothing.
Although I do not foresee that steam mass/volume is the culprit (as per my previous reply), it an interesting suggestion to perform an analysis for completeness.
I may add weighing the milk pre and post steaming for a couple days, keep a log, and see if there is any correlation to be found.

Cheers

JRising
Team HB

#7: Post by JRising »

If there's air in your boiler, then you will be injecting that air into into the milk even with the tip submerged.
(before people tell me that the boiler is only 1/2 full of water, think.) The boiler is almost 100% full of water. The machine has a vacuum breaker that allows the gasses out until after the boiler's liquid water comes to a decent boil. In those three or four seconds of vacuum-breaker hissing, the amount of water that turns to steam is going to be displacing the air above the liquid-line.

If the machine is injecting air that was trapped in the boiler due to a stuck vacuum breaker or something, then the third or fourth pitcher that you froth after the machine has heated should be far better than the first (it has had time to displace most of the air with steam).

Pressino

#8: Post by Pressino »

What JR says explains why the milk still expands when the wand is submerged to any depth in the pitcher. It ought to be evident when you realize what steam is...vaporized water heated to above its boiling point in a closed boiler under higher than outside atmospheric pressure that is released forcefully as pressurized steam from the wand tip when the steam valve is opened. The water is held in the boiler at a temperature well above whatever the ambient boiling point and remains liquid until the steam valve opens to the atmosphere, when it becomes superheated water vapor (i.e. a mixture of air and water) under pressure. As this vapor cools suspended water droplets condense. The water will increase the volume of milk in the pitcher, but to a minor degree compared to the increase in volume due to the injected air.

alexanders5700 (original poster)

#9: Post by alexanders5700 (original poster) »

JRising wrote:If there's air in your boiler, then you will be injecting that air into into the milk even with the tip submerged.
(before people tell me that the boiler is only 1/2 full of water, think.) The boiler is almost 100% full of water. The machine has a vacuum breaker that allows the gasses out until after the boiler's liquid water comes to a decent boil. In those three or four seconds of vacuum-breaker hissing, the amount of water that turns to steam is going to be displacing the air above the liquid-line.

If the machine is injecting air that was trapped in the boiler due to a stuck vacuum breaker or something, then the third or fourth pitcher that you froth after the machine has heated should be far better than the first (it has had time to displace most of the air with steam).
Interesting point, I may have an (occasionally) mis-calibrated vacuum breaker, and maybe it's closing before all the air has been displaced by water vapor...
I only make a single latte for myself in the morning, so I am not able to check the 3rd or 4th milk drink compared to the first.
However, as a precaution, I can try bleeding the steam wand for a little longer before beginning my latte, and try to get more air (if any) out of the boiler, and try to get just the pure water vapor.
I suppose I do vary the length of the steam wand bleed pre-froth. Sometimes I run the wand for 1-2 quick spurts to get the water out of the lines, while other times I may do 3-4 spurts. It kind of depends on how much water I see coming out the wand. Maybe the times I do 1-2 spurts are more likely to be the times that the milk level continues to rise post-tip-submersion.
I'll add this testing to my list!

Pressino

#10: Post by Pressino »

One way to check the progress of pre-frothing "drying" of the steam is to watch the steam boiler pressure gauge while you "bleed" the wand. In my machine (Pro700), I've found that the gauge pressure drops and flutters as water is being bleed from the wand, but after a short period (usually 3-5 seconds), it stabilizes at the steam boiler's set pressure/temperature. That's when I know for sure that the steam is as "dry" as it can be at the boiler's pressure and temperature setting (via the PID).