For many, a coffee without a sweet little something-something just isn't complete. They just seem to go hand in hand. But should you be seeing a donut in your coffee instead of next to it?
In case you were wondering, I'm not talking about a literal sweet donut here. I'm referring to an effect that can have a large impact on the quality of your espresso.
Can you see the donut?
This photo was taken about 20 seconds into the shot. It may look alright here, but soon after things go wrong. In a normal shot, the flow of coffee will cover the whole basket falling into one stream in the middle of the basket. In this case though, the hole in the middle of the shot stays, while the outside pours around it in multiple streams. The colour on the outside quickly changes to blonde, indicating over-extraction in these parts of the coffee. The middle of the basket stays hollow, almost completely dry.
In a naked portafilter like this, the effect is easy to see. A donut ring appears with a hole of unextracted coffee in the middle. In a normal, more traditional portafilter however, there are spouts covering your view of the bottom of the basket. So, this begs the question, how can we tell this is happening?
How to Diagnose
One way is by the colour of the shot. The shot starts normally, however it appears to finish too quickly, going pale and blonding early. It may also be characterised by dark flecks of colour late in the shot. Those dark flecks are caused by coffee coming from closer to the center of the basket, where the shot is running slower compared to the outside.
Flavour can also inform you if your shot has this effect. Espressos with this effect often have a Jekyll and Hyde flavour profile, tasting both over and under-extracted at the same time. The shots lack sweetness and depth.
Now, both of these characteristics can tell you a little, but as we know espresso is a complex beast and other things can cause these results. So is there a definitive way to prove if this is happening without forking out the money for a naked portafilter?
Diagnose by Basket Analysis
When I saw this shot happening in front of me, I knew it was bad. I sure didn't want to taste it to verify my donut suspicions! So instead of just guessing I did a little basket analysis to see make sure I was right.
This is a photo of the inside of the basket after the pour.
Do you notice anything unusual about it? Remember we're aiming for an even extraction of the coffee across the whole basket.
Notice how the centre appears very oily whereas the outside looks cleaner? This is a typical result of the donut effect. The outside is where the water was flowing freely through the basket, washing all the oils into the cup.
The centre is where the hole was. It had no water flowing through, leaving all the oils in the basket.
This is a quick and easy check that I do whenever I have a shot that goes bad unexpectedly.
How to Fix
The donut effect is created by the barista creating uneven density in the basket. The water flows around the outside, through the less dense coffee, missing the denser centre altogether.
To fix this, try to spread and distribute the coffee grinds as evenly as you can across the basket before tamping. If you have a doserless grinder, be sure to move the basket around so you don't end up with a large mound in the middle.
With these tips I hope you find your donuts on the plate next time, rather that in your coffee!