Acidity vs sweetness: How basket design affects espresso extraction

Estimated reading time: 9 minutes

Key takeaways

Perceived sweetness in espresso comes from body, lipids, and crema.
Bright acidity needs sweetness and body to avoid tasting sour.
IMS-Filtri’s NT basket adds clarity, while the Big Bang adds sweetness.
Treat filter baskets as an extraction variable and redial the grind setting when switching between them.

When an espresso tastes too sharp or too thin, baristas usually start with the coffee or the recipe. They adjust the grind size or change the brew ratio, expecting a different result. Yet two shots pulled from the same coffee, with the same dose, yield, and time, can still taste very different, and the filter often explains why.

The filter basket determines how water leaves the coffee puck. Its hole count, perforation pattern, and surface finish all influence flow rate, contact time, and body, which in turn shape how drinkers perceive acidity and sweetness.

“Acidity and perceived sweetness are not fixed traits of the bean: they depend on how we extract it,” says Davide Spinelli, a coffee and cacao consultant with over 20 years of experience across the coffee supply chain. Davide is also a CQI Instructor, Evolved Q Grader Instructor, IMS-Filtri Brand Ambassador, and R&D collaborator.

“The basket should be treated like grind size, temperature, or any other recipe parameter,” he adds. “It’s a lever to be used consciously to design the flavour profile.”

Redefining acidity and perceived sweetness in espresso

Sweetness in espresso has little to do with dissolved sugar. Instead, the palate detects it through several signals at once: taste, retronasal aroma, and the physical feel of the liquid.

“In espresso, sweetness is largely a sensory construction, not a matter of dissolved sugars,” Davide explains.

Three factors contribute to most this effect. The first is the body. In one sensory evaluation of espresso, adding sucrose increased both perceived sweetness and body. The relationship also works in reverse, so a heavier or thicker shot tastes sweeter.

The second is lipid suspension. In a model drink with wine-like acidity, researchers found that adding 0.1% phospholipids produced a detectable change in taste and mouthfeel in a triangle test. Davide compares the effect to the difference between chocolate and cocoa: more suspended lipids give a rounder texture, while fewer leave the cup tasting dry.

The third is crema. One espresso study found that a standard crema layer supports the release of pleasant volatile compounds, whereas too much crema pushes “roasted” notes to the front.

Distinguishing bright acidity from sourness

Acidity, meanwhile, often depends on who is tasting the espresso. Many consumers associate the word “acidic” with sourness. Professionals, on the other hand, see good acidity as a source of freshness, brightness, and structure, much like sommeliers assess wine.

The chemistry overlaps, too. Espresso contains citric, malic, tartaric, and acetic acids, the same organic acids that researchers have studied in juices and wines. Research comparing specialty and commodity coffees found that organic acid concentration predicted perceived acidity in specialty lots, while chlorogenic acids drove perceived sourness in commodity coffee.

According to Davide, the difference between bright and sour comes down to balance. “When acidity is supported by sweetness and body, it’s refreshing,” he says. In an under-extracted shot, however, the same acids lack that support and taste sharp and drying.

To help baristas tell acidity and sourness apart, Davide asks four questions during tastings:

Does the shot make you salivate and leave your mouth clean?
Does the acidity have a recognisable shape, such as citrus, red fruit, or apple, with sweetness underneath?
Does it finish cleanly and persistently, or does it vanish and leave astringency behind?
What happens when extraction runs longer? If sourness falls and sweetness rises, the fault was under-extraction. If the acidity stays and integrates, it’s part of a coffee’s flavour profile.

Why the filter basket matters for espresso extraction

Flow rate, contact time, body, and lipid emulsion all influence how we perceive espresso, and the filter basket’s hole count, pattern, and surface finish determine where water leaves the puck.

As a result, Davide treats the basket as a recipe parameter alongside grind size and water temperature, rather than a passive holder for ground coffee.

Comparing two basket designs

IMS-Filtri’s Cylindrical NT and Big Bang baskets share a 58mm base and a 49mm perforated area, yet they release water in opposite ways. The NT spreads outflow evenly across the base, while the Big Bang draws it towards the centre.

This is because the Cylindrical NT’s hole pattern is uniform across the base, while the Big Bang’s is concentrated towards the centre. The former helps extract espresso with greater clarity and more defined acidity, while the Big Bang produces a rounder body with more perceived sweetness.

With dose, yield, and target time fixed, the two baskets respond differently to puck preparation. With the NT, outflow “is distributed across the entire base”, Davide explains, so a less dense zone, a poorly compacted edge, or a clump “immediately finds a direct escape route”. The NT therefore rewards precise distribution and tamping with a clearly defined cup, but it also exposes small flaws in espresso preparation.

The Big Bang, by contrast, has fewer exit points around the basket’s edge, where water naturally flows faster against the wall. This produces a centred, cohesive stream that tolerates minor distribution errors. “The Big Bang doesn’t eliminate channelling caused by poor prep, but it dampens its effect in the cup,” Davide says.

This matters because channelling forces water through a few paths in the puck, which keeps extraction yield low even at high flow rates.

Puck resistance still comes mainly from the coffee bed. However, the Big Bang’s smaller open area and central convergence change the flow rate enough to shift shot time.

The NT’s Nanoquartz coating protects against corrosion and oil build-up. In Davide’s experience, it also dissipates heat better, which lets baristas run a shot longer or hotter while keeping the cup clean.

Redialling when you switch baskets

Because different filter basket geometries change flow rate, baristas need to adjust grind size when switching between them to keep shot time steady. Davide follows five steps:

Keep dose, yield, temperature, and puck preparation fixed, and change only grind size.
Choose a basket height that suits the dose, so headspace stays comparable. For example, the 23.5mm Big Bang suits 17g to 19g of dark roast, 18g to 20g of medium roast, and 19g to 21g of light roast.
Pull a reference shot at the current grind setting and note how far it misses the target time.
Make small corrections one at a time. Two or three shots are usually enough.
Confirm the result with a refractometer and a tasting.

“The most common mistake is skipping redialling and attributing a difference to the filter that actually stems from brew time,” Davide says.

A few seconds either way changes the contact time between water and coffee, which skews the comparison. The second most common error is changing the dose to compensate, which alters the recipe altogether.

Practical applications for choosing different espresso baskets

A high-altitude natural Ethiopian coffee shows how this works in practice. A study validating The Espresso Protocol as a sensory evaluation method gave the highest quality score to an Ethiopian coffee with a fruity, floral, sweet aroma; a creamy body; juicy acidity; and a persistent finish. This profile combines vibrant fruit with enough body and sweetness to support it.

Davide starts with one question: what should the guest remember about this coffee?

When a coffee is already balanced, the NT helps bring its origin characteristics forward. It suits single-origin menus, tastings, guests familiar with specialty coffee, and espresso served on its own, with defined berry and floral acidity.

Davide switches to the Big Bang in three situations:

When the fruit becomes overpowering, with alcoholic or fermented notes, or acidity that “pricks” rather than refreshes
When the coffee mainly goes into milk-based drinks or reaches a “mainstream” audience
When the roast is very fresh, and the coffee still tastes unsettled

In each case, the centred perforation pattern softens the fruit and “shifts the cup toward a jam-like sweetness”, closer to marmalade than fresh berries.

The same approach helps cafés serve customers who find bright acidity unpleasant. Rather than asking the roaster for a darker profile or changing the brew ratio, baristas can switch to the Big Bang. Its flow pattern rounds out sharp notes and adds tactile sweetness through body and lipid suspension, while the recipe stays the same. Davide also notes the cost difference: a new basket costs far less than a new espresso machine, a reformulated blend, or a change in supplier.

Making basket selection part of the daily dial-in

For head baristas, Davide recommends treating the basket as a standard parameter in every dial-in and building three habits:

Writing the basket on the recipe card next to dose, yield, time, and temperature.
Marking each basket, or assigning it to a dedicated portafilter, so all staff can identify it.
Setting a default basket for each coffee and keeping the alternative as a correction tool.

To check whether the choice is working, Davide tracks four measures:

Extraction data, including TDS, extraction yield, and brew time at equal dose and yield
A structured sensory panel that scores crema, aroma, intensity, sweetness, bitterness, body, acidity, and aftertaste on a five-point scale
Consistency of brew times across baristas and throughout the day
Guest response, including discarded shots, remade drinks, comments about acidity, and sales of straight espresso

Filter basket choice doesn’t replace good puck preparation; distribution, tamping, and cleanliness still come first. Once those are in place, however, filter geometry gives cafés another way to adjust puck resistance, flow rate, and flavour to suit their customers, all without changing the coffee.

For baristas who want to start experimenting, Davide recommends a simple kit: two filters, a refractometer, and a blind tasting.

Enjoyed this? Then read our article on how espresso is changing.

Photo credit: IMS-Filtri

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