I've recently heard baristas suggest pulling espresso shots a bit shorter for milk drinks than for straight espressos. The idea put forth is the shorter shots will have a stronger flavor to stand up in milk versus a more balanced and "weaker" longer pull of espresso. The problem is with lower yield comes less extraction. This means you lose significant sweetness and the espresso becomes more acidic which will not be best for a cappuccino.
Let me give an example. Let’s say you’ve got our new Boloya from Ethiopia dialed in to an 18 gram dose with a 45 gram yield in 27 seconds and it tastes great. The acidity is balanced pleasant peach and floral notes. Now you want to make a cappuccino with a shorter shot so you aim for a tighter ratio at around 30 grams out. If you don’t also adjust the grind you will have to cut the shot off quicker by as much as 8 or 10 seconds. This will give you an ultra light-bodied acidic espresso. Rather than having fruit flavors it could taste generically tart like under ripe peach.
Additionally, the longer recipe gives you more coffee to mix with the milk.
In summary, we generally advise a longer shot recipe for an espresso to go into a milk drink. But as always with any suggestion I make—coffee brewing or otherwise—experiment, taste, and decide for yourself!
Curious about this and want to improve your barista skills? Attend one of my milk or espresso classes!