All coffee guides · Troubleshooting
Crema is the amber-brown foam that sits on top of a well-pulled espresso. It forms when the high pressure of the machine forces carbon dioxide out of the coffee grounds and into the liquid as tiny bubbles stabilised by coffee oils. A thick, persistent crema is often taken as a sign of a good shot, though the relationship between crema and taste is more complicated than it first appears. If your espresso consistently produces no crema or very thin crema, there are a small number of causes to work through.
Crema requires dissolved CO2, and CO2 is a byproduct of roasting that escapes from coffee beans in the days and weeks after the roast date. Fresh coffee — within four to six weeks of roast — retains enough CO2 to produce good crema. Coffee that is several months old or that has been stored poorly has off-gassed most of its CO2 and will produce little or no crema regardless of grind size or machine settings. Check the roast date on your bag. If it is more than eight weeks ago, stale coffee is almost certainly the main cause. This is the first thing to address before changing any other variable.
Crema also requires sufficient pressure to form. If the grind is too coarse, water flows through the coffee bed too easily and the shot runs too fast — the pressure build-up in the puck is insufficient to force CO2 into solution in the liquid. The result is a pale, watery shot with no crema. Grind finer in steps until the shot time is in the normal range (25-35 seconds for a 1:2 ratio) and crema should return, assuming the coffee is fresh enough.
Pre-ground coffee loses CO2 far faster than whole beans because the vastly increased surface area accelerates off-gassing. A bag of pre-ground coffee that has been open for a week may have lost most of its extractable CO2 even if the bag has a recent roast date. Supermarket espresso blends are also often roasted months before purchase and packaged in nitrogen-flushed bags to extend shelf life — they may taste acceptable but rarely produce the crema of fresh specialty coffee. Switching to freshly roasted whole beans and grinding immediately before pulling the shot is the single most effective change you can make for crema.
A machine operating at too low a pump pressure (significantly below 9 bar) cannot force enough CO2 into solution to create stable crema. Most home machines are set correctly from the factory, but OPV (over-pressure valve) springs can weaken over time and some machines are set too high (above 10 bar) by default, which causes channeling rather than crema issues. If you have confirmed fresh coffee and correct grind size but still get poor crema, a pressure gauge portafilter can check whether the machine is hitting 8-9 bar at the puck. Temperature that is too low can also reduce crema formation — ensure the machine is fully warmed up.
Robusta coffee beans contain roughly twice the caffeine and significantly more CO2-generating compounds than arabica. Commercial espresso blends — particularly Italian-style blends — often include 10-30% robusta specifically to boost crema thickness and persistence. Specialty coffee is almost exclusively arabica, which produces a thinner crema that dissipates faster. If you have switched from a supermarket espresso blend to a single-origin specialty coffee and noticed less crema, this is part of the reason. The specialty coffee likely tastes better, but its crema will never be as thick as a robusta-heavy blend.
Crema is a useful indicator of freshness and extraction, but it is not a direct measure of taste quality. Very lightly roasted coffees have less oil than darker roasts and produce thinner crema even when fresh and correctly extracted. Some excellent coffees produce a modest crema that disappears quickly and still taste outstanding. Conversely, a thick, dark crema can indicate over-extraction or a coffee that is too dark-roasted. If your espresso tastes good — balanced, sweet, with appropriate brightness — but has modest crema, the crema is not the problem.
Browse all 98 coffee guides or start a free espresso journal on Baristalog.