Introducing Purity Espresso

For many years, customers have asked Purity to create an espresso, and in honor of National Coffee Day, Purity Espresso Roast joins our lineup this month. But before you pull your first shot, here’s a closer look at what espresso is, how it works, and what makes this roast different.

Where espresso came from

Espresso emerged when Italian inventors added pressure to coffee brewing, along with greater control over the known extraction variables: grind size, dose, coffee-to-water ratio, water temperature, brew time, filtration, device, and roast level. Angelo Moriondo patented a steam-powered machine in 1884, and Luigi Bezzera and Desiderio Pavoni later adapted the idea for individual servings. After the Second World War, Achille Gaggia’s lever machine reached about nine bar and produced crema. Faema’s pump-driven E61 followed in 1961, establishing the model used in modern cafés. [1]

Why it is espresso and not expresso

People get corrected for saying “expresso” all the time. The mix-up is understandable, because “express” has a couple of different meanings.

The Italian phrase is caffè espresso. It refers to coffee prepared on demand and under pressure. The word also connects to the Latin verb exprimere, meaning to press or squeeze out, as in the medical use of “express.” English gets express from the same root, which helps explain why “expresso” sounds correct to many English speakers. The modern meaning of “express” as fast adds to the confusion because espresso is brewed quickly. Still, “espresso” is the correct spelling and pronunciation. [2]

Espresso is a method, not a roast level

One important point: espresso is a brewing, or extraction, method, not a roast level. An espresso machine forces hot water through finely ground coffee under pressure, usually producing a small, concentrated drink in about 30 seconds. [3]

Espresso is not a particular bean, blend, or color. Light, medium, and dark roasts can all be brewed this way. Still, when we know a coffee is intended for espresso, we adjust the roast to bring out certain characteristics, subdue others, and help the coffee taste balanced under pressure.

What makes the result espresso is the full recipe: a fine grind, a concentrated coffee-to-water ratio, temperature, pressure, and a short brew time. The roast does not define espresso, but it can be designed to bring out sweetness, body, and other flavor notes in this brewing method.

What happens inside the machine

With filter coffee, gravity does the work. Hot water moves through a bed of medium-ground coffee and drips into the pot over several minutes.

Espresso uses a pump instead. Water is forced through a tightly packed puck of finely ground coffee at about nine bar (9 ± 2 bar), or nine times atmospheric pressure. A shot is usually finished in about 30 seconds. [3]

Espresso requires a much finer grind than drip coffee. The smallest particles, called fines, have a major effect on the shot. Researchers at the Zurich University of Applied Sciences found that more fines make it harder for water to move through the coffee. As they wrote, "An increase of share of fines decreases coffee bed permeability, leading to reduced flow rates and longer extraction times.” In simple terms, too many fines can clog the filter and slow the shot. [4]

The coffee-to-water ratio is different too. Filter coffee is usually brewed at about 1 part coffee to 16 parts water; espresso is closer to 1 to 2. That combination of less water, more coffee, higher pressure, and less time produces a drink with three to four times more dissolved coffee per milliliter than filter coffee, served in roughly one-tenth the volume. [17,18]

Espresso is also filtered through metal rather than paper, so a different mix of compounds reaches the cup.

The stovetop pot and why it works differently

A moka pot often gets called a stovetop espresso maker. It does brew under pressure, and it does make something small and strong, so the nickname is easy to understand. What happens inside it is a different process, and those differences matter to the finished brew.

Start with pressure. An espresso machine holds about nine bar for the length of the shot. A moka pot works at roughly one to two bar, and that pressure builds as the pot heats rather than holding steady. [6,7,9]

Then there is temperature, and this part makes a big difference in taste.

Many of us were taught that a moka pot pushes boiling water through the coffee. Researchers who put probes inside one measured something else, and they described the boiling water idea as a long-held misconception. On a controlled hotplate, water began moving through the grounds at about 69 °C, well below the 91 to 96 °C range we usually recommend. It averaged 94 to 98 °C across the brew. Then, as the last of the water left the bottom chamber, it reached 117 to 121 °C. That is above boiling, because a sealed pot under pressure raises the temperature at which water boils. [6,17]

In other words, the water moves through a wide temperature range in a single brew: it starts cooler than recommended, passes through the ideal range, and ends much hotter.

That helps explain why moka coffee can turn harsh or have its own characteristic tastes (which can be very different from the same coffee brewed other ways). Studies measured extraction yields of 28 to 31 percent, higher than the other methods they compared and beyond the range where coffee often starts to taste over-extracted. [9,10]

This is why it helps to monitor the pot while it brews. When the coffee coming into the top chamber turns pale and starts to sputter, take it off the burner and cool the base under running water to stop the final, hottest part of the brew. Some people start with already-boiling water to shorten the heating time, but that makes assembly tricky: the base is hot enough to burn you, so use a thick, dry cloth or heat-resistant gloves when screwing the pot together. Many of us have learned that one the hard way.

A moka pot also needs a little caution. It is sealed, pressure builds inside it, and the safety valve needs to stay clear. Recalls filed with the U.S. Consumer Product Safety Commission and Health Canada describe stovetop makers that burst and expelled hot contents, with burns and scalding among the reported injuries. Fill the base below the valve, keep the valve clean, and stay nearby while it brews. [11]

How we choose a coffee for espresso

Because espresso packs so much coffee into so little water, it amplifies everything in the bean. Bright acidity can turn sour, a light body can feel dull, and a processing defect that might disappear in a pour-over can stand out.

We look for coffees that stay balanced under pressure: lasting sweetness, rounded acidity, and enough body to make the shot feel silky rather than thin.

Our health standards come first. Before we evaluate a coffee for flavor, it must meet our green coffee requirements. That includes testing for mycotoxins, heavy metals, and pesticide residue, along with measuring chlorogenic acid and caffeine content. [17]

How we roast it differently from our other coffees

A roast designed for espresso has a different job than one created for filter coffee.

A very light roast can remain dense and difficult to extract under nine bar of pressure, especially within a 30-second shot. Roasting darker makes extraction easier, but it also comes with tradeoffs, like slightly more bitterness and reduced chlorogenic acids (polyphenols).

In one study, researchers brewed the same arabica coffee as espresso and drip coffee at four roast levels. Chlorogenic acids, one of coffee’s most studied groups of compounds, fell sharply at the darkest roast. In espresso, they dropped from 4.96 mg/mL at a light-medium roast to 0.63 mg/mL at a very dark roast. Over the same range, total phenolic content declined 23 percent, and total flavonoids declined 29.1 percent. [12]

That research guided our decision to roast Purity Espresso Roast to about the same level as our flagship coffee, Flow, using different coffees. We did not take a darker coffee and put “espresso” on the label. We developed the roast for even extraction in about 30 seconds while protecting the compounds we prioritize in sourcing. We also confirmed that the carbon dioxide released during roasting forms a lasting crema, the fine, lighter brown foam that rises to the top of an espresso shot. [3]

Comparing espresso and filter coffee

The main differences between espresso and filter coffee come down to the variables a roaster or barista can control. The moka pot is included for comparison.

Variable	Espresso	Moka pot (stovetop)	Filter coffee
Grind size	160 to 250 micrometer burr spacing; fines under 100 micrometers drive the flow [4]	fine to medium, leveled without tamping [9,10]	770 to 1,115 micrometers average particle size [5]
Dose	6 to 8 g for a single, 16 to 20 g for a double [3]	7.5 to 25 g depending on pot size [9,10]	15 g per 250 mL is standard in published work [18]
Coffee to water	about 1 to 2 [3]	between 1:10 and 1:15 [9,10]	about 1 to 16 [17]
Pressure	about 9 bar (9 ± 2) [3]	roughly 1 to 2 bar, building through the brew rather than holding steady [6,7,9]	gravity alone, about 1 bar [5]
Water temperature	92 to 94 °C (198 to 201 °F) [3]	climbs from about 69 °C to 117 to 121 °C (156 to 250 °F) within one brew [6]	91 to 96 °C (195 to 205 °F) [17]
Contact time	about 25 to 30 seconds [3]	about 2 to 4 minutes [9,10]	3.5 to 6 minutes [18]
Filter	Metal basket	Metal basket	Paper, mesh, metal (screen), cloth
Serving size	25 to 30 mL [3]	30 to 60 mL per published cup [9,10]	210 to 250 mL [18]
Dissolved solids in the cup	3.65 ± 0.48 % [18]	2.13 to 3.40 % [9,10]	1.18 ± 0.10 % [18]
Extraction yield	measured 16 to 26 %, with most well-made shots near 20 to 23 % [9,13,14]	28 to 31 %, the highest of any method measured [9,10]	18 to 22 % is the target range [5,15,17]
Roast level	any roast works	any roast works	any roast works

(One note on extraction yield, because those three figures are different kinds of numbers. The 18 to 22 percent for filter coffee is a target. It comes from the Coffee Brewing Control Chart that Ernest Lockhart built at the Coffee Brewing Institute in 1957, which the Specialty Coffee Association carries forward as the Golden Cup standard, and it is paired with a brew strength of 1.15 to 1.35 percent. No equivalent chart exists for espresso or the moka pot yet, so those two figures are what researchers have measured rather than a target anyone has set. [5,15,16])

The next table shows brewed coffee (not dry grounds) results in a study of 18 coffees prepared both ways, allowing a direct comparison. [18]

What is in the cup	Espresso (25 mL from 7 g)	Pour-over filter (250 mL from 15 g)
Caffeine per serving	63.06 mg	185.48 mg
Caffeine per 100 mL	about 252 mg *	about 74 mg *
Potassium per 100 mL	37.63 ± 3.44 mg	21.62 ± 1.27 mg
Potassium per serving	9.41 mg	54.05 mg
Magnesium per 100 mL	4.21 ± 0.55 mg	2.83 ± 0.41 mg
Magnesium per serving	1.05 mg	7.08 mg
Calcium per 100 mL	4.35 ± 0.48 mg	6.53 ± 0.75 mg
Phosphorus per 100 mL	5.67 ± 0.54 mg	4.18 ± 0.35 mg

* Calculated from the study’s published per-serving values.

Chlorogenic acid levels also vary by roast, with the largest drop appearing at the darkest level. [12]

Roast level	Espresso (mg/mL)	Espresso per 30 mL shot	Drip (mg/mL)	Drip per 210 mL cup
Light-medium	4.96	148.8 mg	1.37	287.7 mg
Medium	4.41	132.3 mg	0.84	176.4 mg
Moderately dark	2.85	85.5 mg	0.64	134.4 mg
Very dark	0.63	18.9 mg	0.13	27.3 mg

The filter changes the cup in another way. Coffee oils contain diterpenes, mainly cafestol and kahweol. A paper filter captures and retains most of them; a metal filter allows them through. [19,20]

What the filter does	Espresso and other metal-filtered brews	Paper-filtered drip
Cafestol per cup	1.5 ± 1.0 mg (Italian espresso)	up to 0.5 mg per 150 mL
Coffee oils per cup	60 to 160 mg per 150 mL	under 7 mg per 150 mL

Researchers in Europe also measured how much caffeine and chlorogenic acid moved from the grounds into espresso. A standard shot extracted 65 to 68 percent of the caffeine and 66 to 74 percent of chlorogenic acids. Pulling a longer shot of 43 to 55 mL raised those ranges to 84 to 88 percent and 87 to 94 percent. [21]

There are limits to the comparison: the same extraction percentages have not been published for paper-filter drip coffee, and no single study has measured trigonelline in espresso and filter coffee side by side. For now, those questions remain unanswered.

What the numbers actually mean

The tables make an important distinction between concentration and serving size.

Espresso is far more concentrated. Per milliliter, it contains roughly three times the caffeine and nearly twice the potassium of filter coffee. That concentration is a big part of its flavor and texture.

But a full cup of filter coffee usually delivers more overall because the serving is much larger. In the study, a 25 mL shot contained 63 mg of caffeine, while a 250 mL pour-over contained 185 mg. [18]

So espresso is stronger by volume, while filter coffee can provide more in a typical serving. Confusing those two ideas is behind a lot of common coffee myths.

Meet Purity Espresso Roast

Purity Espresso Roast is a medium roast developed specifically for espresso extraction. It has notes of cocoa and dried fruit, a silky body, and a golden-brown crema. Drink it as a straight shot, add water for an Americano, or use it in a café latte or cappuccino with your choice of milk or milk alternative.

For your first single shot, use this recipe:

1. Grind 9 grams of coffee fine, much finer than you would for filter coffee, into a clean, dry basket.
2. Distribute the grounds evenly, then tamp straight down and level (the bed should be flat, not angled).
3. Aim for 18 grams in the cup in about 30 seconds, with water between 200 and 203°F (about 93-95°C).
4. Adjust the grind first when a shot runs fast or slow, one small change at a time. If the grind doesn’t do what you need, try adjusting the quantity of coffee you use.

Use those numbers as a starting point, not a hard rule. Every machine, grinder, and bag behaves a little differently. Make small adjustments, taste the result, and keep dialing it in until the shot works for you. Once you find the right grind and ratio, you may need to adjust again as the weather shifts and the coffee ages.

However you brew it, Purity Espresso Roast is made to deliver a balanced, flavorful cup while meeting the sourcing and testing standards behind every Purity coffee. We hope you enjoy it, and as always, do not hesitate to give us your feedback, ask questions and let us know how you feel after drinking it for a couple of weeks.

References

1. Illy A, Viani R. Espresso Coffee: The Science of Quality, 2nd ed. London: Elsevier Academic Press; 2005.
2. Merriam-Webster. Espresso vs. expresso: usage history. https://www.merriam-webster.com/grammar/espresso-vs-expresso-usage-history
3. Illy E, Navarini L. Neglected food bubbles: the espresso coffee foam. Food Biophysics 2011;6:335-348. doi:10.1007/s11483-011-9220-5
4. Smrke S, Eiermann A, Yeretzian C. The role of fines in espresso extraction dynamics. Scientific Reports 2024;14:5612. doi:10.1038/s41598-024-55831-x
5. Batali ME, Ristenpart WD, Guinard J-X. Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee. Scientific Reports 2020;10:16450. doi:10.1038/s41598-020-73341-4
6. Navarini L, Nobile E, Pinto F, Scheri A, Suggi-Liverani F. Experimental investigation of steam pressure coffee extraction in a stove-top coffee maker. Applied Thermal Engineering 2009;29(5-6):998-1004. doi:10.1016/j.applthermaleng.2008.05.014
7. Gianino C. Experimental analysis of the Italian coffee pot "moka". American Journal of Physics 2007;75(1):43-47. doi:10.1119/1.2358157
8. King WD. The physics of a stove-top espresso machine. American Journal of Physics 2008;76(6):558-565. doi:10.1119/1.2870524
9. Angeloni G, Guerrini L, Masella P, Bellumori M, Daluiso S, Parenti A, Innocenti M. What kind of coffee do you drink? An investigation on effects of eight different extraction methods. Food Research International 2019;116:1327-1335. doi:10.1016/j.foodres.2018.10.022
10. Gloess AN, Schönbächler B, Klopprogge B, et al. Comparison of nine common coffee extraction methods: instrumental and sensory analysis. European Food Research and Technology 2013;236(4):607-627. doi:10.1007/s00217-013-1917-x
11. U.S. Consumer Product Safety Commission. Recall 22-208: IKEA recalls METALLISK espresso makers due to burn and injury hazards. 25 August 2022. https://www.cpsc.gov/Recalls/2022/IKEA-Recalls-METALLISK-Espresso-Makers-Due-to-Burn-and-Injury-Hazards (see also Health Canada recall notice, 8 June 2022)
12. Jung S, Gu S, Lee S-H, Jeong Y. Effect of roasting degree on the antioxidant properties of espresso and drip coffee extracted from Coffea arabica cv. Java. Applied Sciences 2021;11(15):7025. doi:10.3390/app11157025
13. Cameron MI, Morisco D, Hofstetter D, et al. Systematically improving espresso: insights from mathematical modeling and experiment. Matter 2020;2(3):631-648. doi:10.1016/j.matt.2019.12.019
14. Eiermann A, Smrke S, Guélat L-M, Wellinger M, Rahn A, Yeretzian C. Extraction of single serve coffee capsules: linking properties of ground coffee to extraction dynamics and cup quality. Scientific Reports 2020;10:17079. doi:10.1038/s41598-020-74138-1
15. Lockhart EE. The Soluble Solids in Beverage Coffee as an Index to Cup Quality. New York: Coffee Brewing Institute; 1957.
16. Guinard J-X, Frost SC, Batali ME, Cotter AR, Lim LX, Ristenpart WD. A new Coffee Brewing Control Chart relating sensory properties and consumer liking to brew strength, extraction yield, and brew ratio. Journal of Food Science 2023;88:2168-2177. doi:10.1111/1750-3841.16531
17. Revi I. The Coffee Guide to Better Health: Introducing Circular Health Coffee. 2026.
18. Sijko-Szpańska M, Mystkowska I, Dmitrowicz A. Influence of brewing methods on the bioactive and mineral composition of coffee beverages. Molecules 2025;30(20):4080. doi:10.3390/molecules30204080
19. Urgert R, van der Weg G, Kosmeijer-Schuil TG, et al. Levels of the cholesterol-elevating diterpenes cafestol and kahweol in various coffee brews. Journal of Agricultural and Food Chemistry 1995;43(8):2167-2172. doi:10.1021/jf00056a039
20. Ratnayake WMN, Hollywood R, O’Grady E, Stavric B. Lipid content and composition of coffee brews prepared by different methods. Food and Chemical Toxicology 1993;31(4):263-269. doi:10.1016/0278-6915(93)90076-B
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