The Reason Your Home-Brewed Coffee Tastes Sour
So you've bought a shiny new espresso machine (or whichever brewing equipment that tickled your fancy), snagged a bag of freshly ground beans from your local roaster, heated your water, and assembled everything to pour a cup of home-brewed coffee. You seem to have done everything right only to then find a sour, acidic tang in your java. Is it the rotten batch of beans or dirty water to blame, you wonder — or perhaps some chemical coating lacing your new brewing equipment? Chances are, the problem is far simpler: It's the grind size of your beans.
It all comes down to finding the best grinder setting for your coffee to make the best cup of joe, and that depends on your machine. For example, espresso machines require much finer grounds than the likes of a French press, moka pot, or drip coffee makers. Cold brews are on the very other end of the spectrum and need a much coarser grind size that will produce a texture similar to that of rock salt. Sourness is typically the result of using coffee beans that are coarser than required (like using grounds meant for cold brew makers in an espresso machine instead, for instance). The coarser the beans, the longer the water takes to extract flavor from them. Using them in the wrong equipment could leave you with an under-extracted brew, which will give a noticeably acidic tang to what should be a balanced cup of joe.
Other culprits behind sour coffee
While the wrong grind size is the biggest culprit behind sour-tasting coffees, there are other factors that could leave unsavory flavors in your java too. The main problem here is under-extraction, which is why even the quantity of water that is used, its temperature, and how long it is brewed could play a role in overly acidic coffees. Skimping out on the water, not heating it for long enough, or brewing your coffee for a shorter period than is ideal could all leave your coffee tasting sour.
Another culprit could be the coffee beans themselves, as beans that are over-roasted have a more tart flavor. Other factors could be improper storage of coffee beans and how old they are. Exposure to moisture, air, and sunlight can cause beans to oxidize and produce acetic acid, which in turn gives them an unpleasant bite — whereas stale beans that are several months old and past their prime can have an acidic, lemon-like flavor.
On the flip side, the problem could also be that the beans are a little too fresh! Coffee beans require anywhere between one to three days after they are roasted for their gasses to evaporate and leave balanced flavors in their wake. Brewing the beans too soon after they are roasted could lead to the gasses hindering proper flavor extraction and leaving more sour notes behind instead.
Ways to prevent your coffee from tasting sour
Knowing what's causing your coffee to taste sour will bring you one step closer to fixing the problem. For example, if all signs point to the grind size, pop the coffee back in your grinder and do it again. It's also important to consider the type of grinder you're using: Blade grinders are notorious for producing uneven grounds that don't brew properly and leave a tinge of sour flavor. Consider picking a burr grinder over a blade one for more uniform grounds and better flavor extraction instead.
Otherwise, the solution will depend on the type of equipment that you're using. For example, different equipment requires different bean-to-water ratios, so read the instructions that came with your coffee maker to find the perfect ratio. Warm your water to a temperature between 195 and 205 degrees Fahrenheit for hot coffees — any lower, and your under-extracted coffee will have a sharp tang. Make sure to always keep your machines clean, and only use fresh water to brew your coffees to prevent sour-tasting coffees. If you've already brewed a sour coffee and don't know what to do now, fret not; it's not too late to save the day yet — simply add a splash of cream or stir in a sweetener to balance the flavors!