Stove top coffee makers, such as the iconic Bialetti Moka pot, are great machines for making delicious coffee at home which do not take up precious counter space or need preheating, and are relatively simple to maintain.
Traditional Moka pots and similar stove top makers work by forcing pressurised (around 1 bar of pressure at most) hot water through the coffee grounds, where the pressure is generated by boiling the water.
Although these machines can make a strong coffee, they do not reach the pressure levels needed to produce what is generally considered true espresso.
What is Espresso?
A cup of espresso with crema
Lets first establish what we are referring to when we talk about 'espresso'. Coffee beans have been brewed in many ways by various cultures for centuries, resulting in a wide array of brewing methods.
Fundamentally, a cup of coffee is made when ground coffee beans are infused in hot water, resulting in the delicious drink we all know and love. There are countless methods through which people can do this whether that's using a French press or drip coffee to traditional or manual espresso makers. Whilst all of these methods are fantastic ways to make delicious coffee, espresso has its own unique characteristics.
Espresso is a concentrated form of coffee, with a rich flavour and is generally used in milk-based drinks like lattes. The etymology of the word 'espresso' comes from the Latin word for 'express' and can be translated from Italian as literally meaning 'pressed out'. The brewing process involves forcing pressurised hot water (typically at 9 bars of pressure) through a finely ground bed of coffee beans.
Compared to other stove top coffee makers, espresso machines need a much finer grind size to produce proper extraction. Grinding finer increases the surface area of the coffee in contact with the brew water, allowing for higher extraction levels and significantly higher concentrations of delicious coffee oils and compounds in final brew. This is what gives true espresso its characteristic thick, syrupy texture. Generally speaking, espresso does not contain any new or different flavours present in most coffees, but these flavours tend to be amplified by this style of brewing
One of espresso's defining traits is its 'crema' - a thick, golden layer that sits on top of your shot. The crema is formed when carbon dioxide present in the coffee beans dissolve into the liquid and emulsify with the soluble oils, forming the crema. Coffee connoisseurs swoon over the appetising appearance of this layer, and always strive to produce espresso with great crema.
To summarise, the 3 key ingredients for great espresso are:
Brewing Coffee with a Moka Pot Style Maker
Commonly, stove top coffee makers like the Moka pot are marketed as being 'espresso makers', and whilst they certainly have similarities they do not produce the same end result.
Lets start by looking at the mechanics. A conventional stovetop or Moka Pot brewer has three key parts: a boiler, a coffee basket and a reservoir for collecting the final brewed coffee. When placed on the stove, the water temperature reaches around 100°C, which causes steam to build up. The steam exerts pressure on the water, and this pressure forces the water out of the boiler, through the un-tamped coffee grounds and into the reservoir. Whilst these conditions do produce pressurised brew water, typically it does not exceed 1 bar of pressure. An espresso machine, on the other hand, will brew at 8-10 bars of pressure which is significantly higher.
Since there is no means to cool the pressurised water in a standard stovetop brewer, this means that the actual brew temperature can exceed 100°C. These conditions mean that coffee produced with this style of brewer can lead to an over extracted and bitter flavoured coffee. However, this is not to say that all coffee produced with Moka pot style brewers cannot produce well balanced coffee, more that these brewing conditions can make this challenging.
A diagram demonstrating the mechanics of a Moka pot
A traditional espresso machine is often a fairly substantial piece of equipment with its own built in water tank, pressure gauge and more often than not a steam wand to make perfectly textured milk to pair with your espresso. Your local coffee shop will almost certainly make all their coffees using espresso machines, and more seasoned coffee drinkers will have their own home espresso maker.
Not only will these machines reach 8-10 bars of pressure, but they will be able to acutely regulate the brewing temperature. This means that espresso is brewed at a much lower temperature than a traditional stove top coffee maker. Espresso machines will usually brew between 90°C and 96°C, and this temperature will remain consistent throughout extraction with some of the more high performance machines.
Compared to drip coffee, stovetop coffee produced by something like the Moka pot is typically 2/3 times stronger. The final brew will be dark, bold and strong in its flavour, although that's not to say coffee produced in this method cannot be sweet or floral but it is certainly challenging to produce these flavours due to the nature of the brewing conditions.
Whilst espresso is also a more concentrated type of coffee, it is far stronger than that produced by Moka pots. Espresso shots tend to be very intense on your taste buds (in a delicious way) and possess a rich flavour profile. Perfect espresso is often well balanced with a palate that is full of complexity and flavour.
Espresso is a delightful but demanding pursuit. Its intense concentration means that even the smallest change can have significant impacts on the flavour of your shot, whether that's for the better or for the worse. There is certainly more of a learning curve to brewing perfect espresso and it can be exasperating at times. However, the reward of a delectable coffee, full of flavour and complexity with great crema is certainly worth pursuing and a journey worth embarking on.
Traditional stovetop brewers or Moka pots, while not a walk in the park, do offer a more gentle learning curve compared to espresso. Mastering this type of coffee does equally require some research and experimentation, but not in the same way as espresso.
Stove Top Espresso and the 9Barista
9Barista stands alone amongst traditional espresso machines and stovetop brewers - it is the only stove top coffee maker that actually brews true espresso and is inspired by the mechanics behind jet engines. How does it do this?
The Lower Boiler
When the 9Barista is placed on the stove, the brew water in the lower boiler reaches 100°C, but, unlike a traditional Moka pot style brewer, this water is prevented from reaching the coffee due to a spring loaded valve.
A diagram demonstrating how 9 bars of pressure are generated in a 9Barista
Because the lower boiler is sealed, the brew water continues to heat, until it reaches 179°C, at which point the water has also reached 9 bars of pressure. This pressure forces the spring loaded valve to open, allowing the hot water to continue towards the coffee.
A diagram demonstrating pressurised water leaving the lower boiler and entering the upper boiler
So, we have our first espresso ingredient: 9 bars of pressure. However, at 179°C, our hot water is at risk of burning and over extracting our coffee grounds. It needs to be cooled down, and fast; that's where the upper boiler comes in.
The Upper Boiler
Unlike the lower boiler, the upper boiler is not sealed, steam is vented via the chimney. This means the hottest the water can get is 100°C, unless you are brewing coffee on a mountain (it does happen…).
When the hot water leaves the lower boiler, it passes through the heat exchanger. This is a series of coils which are submerged in the hot water contained within the upper boiler. Since the coils are submerged in a stable 100°C water bath, the brew water rapidly cools from 179°C to 100°C. Before reaching the coffee, the brew water is further cooled to 93°C by the air cooler. These are the (in our opinion) rather cool looking fins just below the handles.
A diagram demonstrating pressurised hot water rapidly cooling in the upper chamber
Finally, the brew water, at 9 bars of pressure and 93°C, hits the puck of coffee. Because the 9Barista brews at such high pressure, it needs finely ground, tamped coffee - the same as what your local coffee shop would need for their espresso machines. With this, we have all the ingredients needed to make perfect espresso with great crema. The results are a double shot of thick and syrupy espresso, full of flavour.
A diagram demonstrating water at 9 bars of pressure and 93°C extracting espresso
It is the incorporation of this patented double boiler system which enables 9Barista to produce true espresso from the stove top. So whilst aesthetically it takes inspiration from traditional stovetop brewers, there is far more than meets the eye with this machine and it is why (we think!) it is a fantastic option for producing café-quality espresso from the comfort of your home without investing in a large piece of equipment.
Of course, everyone's coffee tastes are different and we are a community of people open to constant re-invention and re-imagining of brewing techniques in order to achieve delicious coffee. But, if its espresso you're after, a bona fide espresso maker is the way to go (of course, we recommend the 9Barista!), and whilst stove top coffee makers like the Moka pot do make delicious coffee, sadly, they do not produce a true espresso.
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