I often find that standard espresso shots at many high-end coffeeshops to be more sour than I prefer. I tend to order straight espresso, or Americanos with only a little water, or maybe a macchiatto, so there's not much fat to cut the tartness. What should I say to get a less acidic shot?
Here's a few thoughts based on what causes sourness/acidity in coffee and ways to temper it.
Order an espresso lungo. Sourness (acidity) is characteristic of the "stuff" that is extracted relatively early in the brewing process. In other brewing methods that take longer to perform (e.g., coffee press, drip, or pour-over) this can be balanced by the more bitter notes that take somewhat longer to fully extract. For this reason, you might get a result that is more appealing to you by ordering an espresso that takes longer to pull, i.e., espresso lungo. Not everyone behind every coffee counter will be immediately familiar with this, but at good cafes with good machines an espresso lungo should be no problem.
Try a darker roast. Darker roast coffees tend to be less acidic than lighter roasts, at the expense of losing more of the varietal/regional notes. Many cafes have really only one bean/roast that they use for every espresso (often because of the practical considerations of having several grinder hoppers full of beans), but if you have an option, try a darker-roasted bean.
Try beans from a different region. To my taste, Indonesian coffees tend to have less pronounced acidic notes than African or American coffees. Again, if multiple coffees are available for espresso, pick a coffee that you like (or find less sour) for any other preparation.
Pick beans further off of the roast. This is really only for completeness, but beans that were very freshly/recently roasted (i.e., less than a few days) can have accentuated acidity because some undesirable volatiles haven't yet had a chance to leach out. This is more toward what @daniel noted; this is the kind of thing you shouldn't need to be concerned about at a cafe -- they should!
A cafe affiliated with a local roaster (or any specialty cafe) should be able to tell you lots of things about the coffee when asked, such as region, varietal, roast level, and roast date. Here's a Serious Eats article about "problems" and related solutions that touch on some of the things I talked about above. Here's another link from Coffee Cuppers about regional and roast considerations in general.
Taste is subjective but a high-end espresso should not taste sour. Old coffee, poorly roasted coffee, and inferior grade coffee are the main culprits.
The following is a pet theory, not science: cafes that charge a lot for coffee to cover overhead--or just because they think they can--sometimes have a low regard for the customer. Sometimes the best cup of espresso comes from a smaller cafe that depends on loyal customers for survival or is in business because the owner takes pride in serving good stuff.
You shouldn't have to say anything to get a less acidic shot. If you are paying for good espresso you should get it--with the qualification that any cafe has a cycle of re-stocking and so some variation in quality is normal.
As it was already mentioned some of the main parameters determining coffee taste are:
- beans origin and quality.
- beans roasting and time passed.
- beans grounding and time passed.
- water quality.
- water desalination frequency.
- general cleanliness of the machine and the environment.
- lower water temperature of extraction. If the machine temperature is lower due lack of periodical calibration, the coffee tastes sour and flat.
- extracted coffee exposure to the atmosphere. The longer is stays exposed, the more it reacts with the atmospheric oxygen and oxidizes, thus becoming more sour. This is true especially for all the coffees with added water (Americano, lungo) that breaks the thin layer covering and preserving the coffee's nice taste qualities.
Consumption of additional beverage or/and snack together with the coffee.
if the additional food or/and drink consumed together with the coffee contains more sugar, then your coffee will always taste sour. (The effect is similar to when you eat chocolate first and then eat an apple, the apple tastes much sour.)
smoking affects taste receptors as well and it should be taken into consideration, i.e. you receptors are less sensitive and there is no point in buying coffee from high-end shops, as you are unable to feel the taste.
Generally, if you want to experience the best quality of a given espresso, you should order it ristretto. The ordinary espresso extraction time is around 25 seconds (1ml / sec) and you get a full shot. Ristretto reduces the extraction time, usually by half, and cuts the last drops of water that contain lower concentration of coffee extract, thus keeping the strong aroma and different taste balance. In the ideal case it should be consumed as fast as possible, just like a gourmé meal.