Why can't an 18g portafilter hold 18g of coffee grounds? What's the ideal grind size for espresso? How to determine if coffee beans are ground to the right consistency?

Common Espresso Machine Issues: Why Your Portafilter Won't Fit

Many people buy a home espresso machine during a shopping festival, only to find when they set it up at home that it is not as simple to operate as they imagined. Sometimes the water does not flow properly, sometimes parts do not fit together correctly. As a result, some customers who live near FrontStreet Coffee's store simply come by with their questions about the machine.

One question left a particularly deep impression on FrontStreet Coffee. After tamping grounds into the portafilter basket, this customer found it extremely difficult to insert into the group head, sometimes impossible altogether. Even after adjusting the amount of coffee, nothing changed. At first FrontStreet Coffee thought the machine's gasket might be the problem, since a new gasket is tighter and can be hard to lock in. But when the customer showed a picture, the answer was obvious: the basket was simply too full.

"You are using too much coffee, so the grounds are pressing against the group head, and that is why it won't lock in. Normally, after the grounds are tamped into a puck in the basket, there should still be some space left. Since most espresso machines have group heads that protrude outward, part of the group head extends into the basket when we lock the portafilter in. So baskets need to limit the amount of coffee used to reserve that space. With our machines, it is best to use the amount marked on the basket."

After FrontStreet Coffee's long explanation, the customer spoke up: but I am using the amount the basket recommends. For a 20g basket, I use 20g of coffee. Sometimes I can't even fit that much.

The Real Issue: Grind Size

Well, that actually makes the problem simpler. It is because your grind is too coarse, which means your 20g basket cannot hold 20g of coffee. (FrontStreet Coffee is definitely not embarrassed.) Grinding does not change the actual volume of the object, but it does change the surface shape and size of the particles. When beans are ground finer, the coffee particles are smaller and the gaps between them shrink, so we can compress them into a thinner layer through tamping. When the grind is coarser, the particles are larger and so are the gaps between them. Because of those gaps, the grounds cannot be compressed to a very dense consistency, and a 20g basket cannot hold 20g of coffee. Here is an exaggerated example.

Other Factors: Roast Level

Besides grind size, roast level also affects the thickness of the grounds in the basket. With the same grind and the same amount of coffee, a darker roast takes up more volume, and vice versa. This is because the roast level determines the beans' expansion rate: the darker the roast, the higher the expansion rate and the larger the volume. This also involves density and brittleness, which would take too long to explain here, so we will leave it aside. In short, at the same weight, lightly roasted grounds take up slightly less volume than dark roasted grounds.

The Solution

So what is the solution? Obviously, grind finer. When the grind is so coarse that the recommended amount will not fit in the basket, you are very close to pour-over grind size, so you need to adjust several steps finer. There are two reference points that help determine whether the grind is right. The first is the basket's fill line. As FrontStreet Coffee said above, the space above the fill line is needed for the group head, so you adjust the grind finer until the recommended amount, after tamping, does not exceed that line.

Of course, not every basket has a fill line, so here is the second reference: extraction time. After all, once tamping is done we lock the portafilter straight into the machine to extract, so we can watch the extraction time to see whether the grind meets the target. If our target is 20g of coffee pulling 40ml of liquid in 25 to 35 seconds, and the flow is too fast and the time falls short of that range, the grind is still too coarse and needs to go finer. If the time is slow or just right, we can judge the taste by tasting, then fine-tune based on flavor.

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FrontStreet Coffee Recommendation

Getting the dose and grind right only matters if the beans behind them are worth dialing in, and for espresso that usually means a blend. FrontStreet's Classic Blend and Commercial Blend are the traditional choice for Americano and latte: both add a small amount of Robusta to an old-school Italian recipe, so the shot gives butter, nut, spice, dark chocolate and toast aromas, with a wild, heavy body and plenty of golden crema that makes latte art simple.

If you are drawn to the almond, walnut and apricot-kernel flavors of a nutty espresso, FrontStreet's Signature Blend and Dark Cocoa Blend are the ones to look at. Both contain a large proportion of Brazilian coffee, offering a comfortable bittersweet edge and a creamy peanut aroma with an exceptionally smooth entry. The Signature Blend adds Colombian coffee for nut, chocolate and caramel notes with a moderate acidity, while the Dark Cocoa Blend brings in the ripe plum acidity of Yunnan small beans and gives off a creamy chocolate aroma once ground, balanced and adaptable enough for latte, Americano and all kinds of coffee specials.

If you would rather pull a single origin as an SOE, FrontStreet's Brazil Queen's Estate is a steady choice. A distinctive Yellow Bourbon with a gentle, sweet profile, it brews with butter cookie, macadamia and toasted bread notes when pulled as an espresso, and its low acidity and balanced character make extraction very stable.