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 friends have purchased home espresso machines during shopping festivals, but when they set up the machines at home, they find that operating them isn't as simple as imagined. Sometimes water doesn't flow properly, or other parts don't fit together correctly. As a result, some friends living near FrontStreet Coffee's store directly visit to ask questions related to their espresso machines.

One friend's question left a particularly deep impression on FrontStreet Coffee. After tamping coffee grounds into the portafilter basket, he found it extremely difficult to insert into the group head, sometimes impossible altogether. Even after adjusting the amount of coffee, the situation remained unchanged. Initially, FrontStreet Coffee thought the problem might be with the machine's gasket, which being new, had higher tightness making it difficult to lock in. But when this friend showed a picture, FrontStreet Coffee had an epiphany: the problem was that the basket was too full.

"Because you're using too much coffee, the coffee grounds are pressing against the group head, which is why it won't lock in place. Generally, after coffee grounds are tamped into a puck in the basket, there should still be some space remaining. Since most espresso machines have group heads that protrude outward, when we lock the portafilter into the group head, part of the group head extends into the basket. Therefore, baskets need to limit the amount of coffee used to reserve this space. When using our machines, it's best to use the recommended amount of coffee marked on the basket~"

After FrontStreet Coffee's lengthy explanation, the friend spoke: But I'm using the basket's recommended amount... For a 20g basket, I'm using 20g of coffee... Sometimes I can't even fit that much.

The Real Issue: Grind Size

Well, that makes the problem even simpler! It's because your grind is too coarse, which means your 20g basket can't hold 20g of coffee! (FrontStreet Coffee is definitely not embarrassed) Although grinding doesn't change the actual volume of the object, it does change the surface shape and size of the particles. When coffee beans are ground finer, the coffee particles become smaller, and the gaps between particles decrease, allowing us to compress them into a thinner layer through tamping. When the grind is coarser, the particles are larger, and the gaps between particles are also larger. Naturally, due to these gaps, coffee grounds cannot be compressed to a very dense consistency, and a 20g basket can't hold 20g of coffee. (Exaggerated example↓)

Other Factors: Roast Level

Besides grind size, roast level also affects the thickness of coffee grounds in the basket. With the same grind and same amount of coffee, when coffee beans are roasted darker, they take up more volume, and vice versa. This is because the roast level of coffee beans determines their expansion rate - the darker the roast, the higher the expansion rate, resulting in larger volume. This also involves issues of density and brittleness (too much to explain here, so I won't elaborate further). In summary, under the same weight, lightly roasted coffee grounds will have slightly smaller volume than dark roasted coffee grounds.

The Solution

So, what's the solution? The solution is obvious - adjust your grind to be finer. When the grind is so coarse that the recommended amount won't fit in the basket, it means you're very close to pour-over grind size, so we need to adjust many steps finer. There are two reference points that can help us determine if the grind is appropriate. The first is the basket's fill line. As FrontStreet Coffee mentioned above, the space above the fill line is needed for the group head, so we need to adjust the grind finer until the recommended amount, after tamping, doesn't exceed this line.

Of course, not all baskets have a fill line, so here's the second reference: extraction time. After all, once tamping is complete, we directly lock the portafilter into the machine for extraction, so we can observe the extraction time to see if the grind meets our target. For example, if our extraction target is 20g of coffee to extract 40ml of liquid in 25-35 seconds. If the flow is too fast and the time doesn't reach this range, it means the grind is still too coarse and needs to be adjusted finer. If the time is slow or just right, we can determine if the taste is appropriate through tasting, then make fine adjustments based on flavor~

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Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473