In the search for all the pieces to the Latte Art puzzle there are a number of factors that are involved. As we saw last week, the size of the holes on the steam tips is just one of these factors. This week we'll see that the size of the hole is perhaps not the absolute factor that it appears to be.
Oooo, the plot thickens.
Unfortunately, there is a limit to the number of machines that I can discuss with respect to the influence of the steam tips, and their ability to create Latte Art foam. Despite the whole whack of espresso machine manufacturers out there, two brands that saturate the market in Vancouver; Nuova Simonelli and La Cimbali. Given the frequency with which I encounter La Cimbali and Nuova Simonelli machines in Vancouver, unlocking the steam tip riddle with each of these brands became paramount. My beloved Conti Catronic is one of only two in the city. Some other names that make an appearance, albeit rarely, are Wega, La Spaziale, Faema, La Marzocco and a few Rancilio hydraulic machines bring up the rear. In the JJ Bean stable we find two La Cimbali M28s, a Nuova Simonelli, the venerable Conti and a recently added La Marzocco FB 70 (3 of them actually). Let's examine the particulars of the La Cimbali, Nuova Simonelli and La Marzocco steam tips and the success of pouring Latte Art with each.
We'll begin with a little background on steamwands, steam tips and thread patterns. La Cimbali and Nuova Simonelli offer different steamwands. Very generally, there are wands that are made with stainless steel and those that aren't. The steam tips found on the stainless steel wands tend to be better at creating Latte Art foam than those found on the non-stainless wands. This would be no big deal if the thread pattern of the wands was maintained. In the case of the La Cimbali wands the thread pattern is the same, which makes switching tips a breeze. However, for the Nuova Simonelli the thread pattern differs between the stainless steel and non-stainless steel wands. This makes switching steam tips between models, let alone between manufacturers nigh to impossible.
Late breaking news and as yet unverified information (although my source is solid) indicates that Nuova Simonelli is now standardizing the thread pattern on their steam wands and that in fact Cimbali tips will fit this new thread pattern. Bring in the Hallelujah chorus.
Have a look at the La Cimbali steam tips. The one on the left is the tip that typically finds it's way onto the non-stainless steel steam wands. It sucks donkey, and can't make dense foam worth a lick. However, the tip on the right has been my salvation. It is the more expensive stainless steel tip, standard on stainless steel steamwands, and also available aftermarket. The steam tip on the right makes Latte Art foam with aplomb. As mentioned previously the thread pattern is the same on all the Cimbali wands (stainless and non). An upgrade to the beautiful foam guaranteed, small hole stainless tip, is therefore easy regardless of which model machine you are using.
(NB: Cimbali has different dispersion patterns in their stainless tip line up. I only guarantee results with the above tip.)
Next are steamwand tips from a Nuova Simonelli. The dispersion pattern seems to be more at work here than the size of the holes. On the left, the lower end tip, with a narrow dispersion pattern. On the right, the higher end stainless steam tip with a marginally broader dispersion pattern. The tip on the right is the better of the two, although it still doesn't make creating Latte Art foam as easy as either the Conti or La Cimbali steam tips previously mentioned. What's worse is that the thread pattern on the low end wands won't thread the stainless tips. To upgrade to the better stainless steel tip (and it's a small upgrade at that) you have to change to the whole (damn!) stainless steel steamwand. Sigh.
Finally, the La Marzocco tips, perhaps the exception that proves the rule. The first day we had the machine people were saying to me "Aaron, I just made the best foam I have ever created on this machine." Whoa, cool. For me the steam tips on the LM have never been in doubt. In the land of Latte Art (Seattle), the LM is the machine of choice. If you can't create Latte Art using the LM then it ain't the machine's fault, it's you! A quick glance at the steam tips on the LM, and YIKES, the holes are pretty big. Definitely equal to the size of the holes on the La Cimbali and Conti tips that I couldn't beg Latte Art foam from. I can however create Latte Art foam on the LM, so what gives? Anyone from the class?
Here's my theory. The aperture of the holes in the steam tip must match the steam pressure of the boiler driving the wand (all other things being equal). Let's assume that there is (for Latte Art foam) an ideal steam velocity leaving the steam tip. The lower the boiler pressure the smaller the hole required to achieve this velocity, the greater the boiler pressure the greater the hole allowable to create the same velocity of steam exiting the steam tip. A quick look at the design of the La Marzocco vs. other espresso machines sheds some light on this theory.
Most espresso machines (including La Cimbali, Nuova Simonelli, and most others) are single boiler, heat exchanger type machines (for a thorough explanation of heat exchange vs. dual boiler espresso machines talk to Terry Z the inhouse espresso machine expert here at CoffeeGeek). In a heat exchanger espresso machine the temperature of the brew water for the espresso is dependent on the pressure that the boiler is set at. The ideal temperature of the water for espresso is agreed to be in a narrow range, and corresponds to a boiler pressure between 1.1 - 1.3 bar. This boiler pressure is not enough to drive a steam tip with big holes. These machines excel (i.e. have the best performance and thermal stability) when used primarily for pulling successive shots of espresso with limited steaming of milk.
Maybe ideal in Italy. Here in the land of the latte where we smother our espresso with buckets of milk, steaming capacity is paramount. One solution for this is the dual boiler set-up made famous by La Marzocco. One boiler is dedicated to the brew water for the espresso. The temperature of this water can be adjusted accurately and independently of the boiler pressure. The second boiler is dedicated to creating steam and in turn it's pressure setting has no impact on the temperature of the brew water. Therefore the steam boiler on the La Marzocco can, and does have its pressure set much higher than what can be done on a heat exchanger machine. The recommended boiler pressure for the LM is 1.5 bar. The larger holes on the steam tips of the LM are more than compensated for by the significantly higher pressure of the steam boiler driving the wands.
To be perfectly honest, the theory behind why small hole steam tips work the best interests me far less than just knowing that it works. Try a small hole steam tip for yourself and see. You'll create foam that excels at pouring Latte Art and gives you a drink with a texture and a creaminess in your mouth that is beyond compare.
Learning to pour latte art is hard enough as it is without your espresso machine working against you. Ask your rep for what's available. Most manufacturers do make a handful of different style tips.