I recently had a really great chat with a gentleman responsible for designing a manual lever espresso machine, a very great one at that!
In our talks, the topic of pressure gauges came about. A pressure gauge, recently was added to the update model of this brewer and is found on many other pieces of equipment (something we both agreed, the market is asking for).
We started discussing how critical it really is to hit 9 bars of pressure. It came up that he had been using a brewer for years without the gauge, drinking really tasty shots, just using instinct and feedback from the taste itself. When the guage was added, it was noticed that extractions were more in the realm of 6-7bar. When adjusting everything to achieve 9bar, it could be difficult to chase consistently and the shots didn't necessarily taste better, infact sometimes not as good.
My response to all this, I wasn't really that surprised. Now this isn't to say that 9 bars of pressure is bad by any means. It can produce some very tasty cups, it just shouldn't be what we are chasing in our extractions.
This got me thinking, and inspired me to write today's post. I worry sometimes people focus too heavily on pressure and fear that these gauges, can sometimes be more of a hinderence than a help.
I will start here, I have nothing against pressure gauges, infact a lot of my equipment has them and I love having all the information and feedback when brewing. I'm a coffee geek, very pro scales, thermometers, guages and anything else that provides more feedback about the variables in coffee. The more we can measure, the more chance we have of achieving consistency in our brews.
The trap many fall into is starting to chase this 9 bar target, like it is crucial to them having a tasty espresso. I am often asked about what is the best pressure and how does it effect the cup. I am hoping this helps shed some light on it all, at very least helps you to stop relying so heavily on that guage and just to start seeing it as one of many factors involved in a good extraction.
Do I need to hit 9 bars of pressure?
Short answer, no not really. Extraction is a complicated beast, one we are still learning lots about. It wasn't long ago that turbo shots were blowing everyone's mind and making us rethink espresso as we knew it (spoiler alert, your turbo shots aren't even coming close to 9bar and these are one of the most efficient extractions that can be achieved in espresso).
This is a topic I have explored and tested for many years. Infact my dual boiler machine has been dialled back to 6 bar for around 4 years and very rarely do I up the pump pressure to 9 bar unless I am chasing something very specific or carrying out tests and experiments.
Some quick notes on tests we have competed over the years, when first exploring 9 v 6 bar. Using a refractometer to measure total dissolved solids (TDS) and in turn extraction yield (EY), the finding of 20 shots each, pulled with the same coffee, equipment, recipe and preperation was surprisingly very similar.
- Both the 9 bar shots and the 6 bar shots fell in an acceptable extraction range of of 18-22%.
- The 6 bar shots had a lower standard deviation than the 9 bar.
- The mean (Average) of 9 bar extraction yield, was lower than that of the 6 bar extraction.
For the people whom like to see some more in-depth figures:
Mean EY%: 9Bar 20.01% VS 6Bar 20.97%
Median EY%: 9Bar 20.00% VS 6Bar 20.9%
Mode EY%: 9Bar 19.2% VS 6Bar 20.9%
Stan Dev: 9Bar 0.89 VS 6Bar 0.46
9 bar profile Vs. 6 bar profile.
You may have noticed some small differences in the figures above. This doesn't however explain how a shot tastes, this should always be our final measure of the quality, the figures are a bit like the pressure gauge, more feedback to assist in us creating and replicating tasty coffee and not what determines tasty coffee.
Now this is the important factor, how did the coffees taste and what was the difference between them.
I want to start by saying both methods produced some really tasty shots for both milk and black coffees.
Overall the taste of the 9 bar shots tended to have slightly more astringency, less precived sweetness and sometimes with a slightly thicker body, there were outliers that seemed considerably thinner in body too. Also a couple outliers that were really sweet and syrupy.
The 6 bar shots, as a whole, tended to produce more fruit notes, balanced sweetness, acidity and a creamy body. Overall tended to be more similar to each other and the feedback was preferred by our blind tastings for milk and black coffees. The difference was definitely more precived in the blacks than milk, as to be expected.
I don't have a pressure gauge, how do I know where my pressure is?
I am hoping this post helps people realise a couple key points.
There is nothing wrong with 9 bar pressure, however it isn't the key to great espresso, like it is often made out to be.
6 bar also produces great tasting shots, as will pressures inbetween the range of 6-9 bar.
The key, with manual espresso is to use your instincts and pay attention to how the shot feels while you are extracting. Taste each shot and really take note of the differences in flavour, you will start to learn what feels like the right pressure.
This is something hard for anyone to convey in words, it comes with experience. As a start you want to feel pressure and resistance, but if it feels like you have to strain yourself so hard, it may not be helping and possibly may be creating channeling (by now you have had someone tell you water is lazy and it will always find the path of least resistance).
Just keep in mind how it feels, taste the shot and try replicate what is tasting good. If the results are good, it doesn't matter if it's 6,7 or 9 bars of pressure, as long as you can keep doing it each time.
Conclusion
Overall I prefer (as did the people we did blind tastings with) the profile and flavours of the 6 bar extractions. The 9 bar extractions were still tasty and while the results seem to favour the 6 bar shots, both methods were still in the thresholds and tolerances deemed to be acceptable shots to serve.
Something we noticed, the tolerances of what tasted exceptable for 6 bar extraction, in water contact time was wider. Leading us to believe that the lower pressure reduces the amount of channeling, the resistance in the coffee bed is lower. Creating more even extractions and increases the exceptable extraction window.
Lower pressure gives us the opportunity to grind courser while still remaining in our targets, reducing fines in the grind. This may be one reason the espresso at 6 bars seemed to be less harsh and more balanced and also why 9 bars tended to have a slightly heavier body.
Most importantly of all, taste your shots and see what works for you. If it's tasting good and you are getting consistent results, who cares what pressure you are hitting! This goes for manual espresso and in line pump machine.
Hope this helps some of you decode the mystery of pressure and helps you look at your coffee from a different angle.
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