A few weeks back, with a little help and encouragement from London’s finest Coffee machine engineer and Dungarees partner, Nic Barnett, we decided to question our PRESSURE PROFILING. For a week of trading we noticed that our usual espresso extraction was consistently running very ‘lively’ (underextracted). Being a mobile coffee maker, in the past we have had to go through stints of heating the water with the gas setting on our dual fuel machine, which was seemingly one strong reason for this ‘liveliness’. The flaming heat created within the framework of the machine was causing distinct differences and raging inconsistencies. Dual fuel machines are an interesting topic for a later post, but running off gas is something we certainly avoid when we can. Having a consistent power source with electricity and the boilers element is far favourable and sought out by us whenever possible at events and festivals. So, having not used gas for some time we started to see the old inconsistencies creeping back into our shots. But why??

With dual fuel machines, which are seen on many mobile units, regularities in the variables are harder to come by. To reduce inconsistencies with your machine, which are ordinarily addressed with a built in PDI system, we have become masters at using our senses to maintain consistency in our coffee. Although this takes much more concentration and care, and is not ideal, it has paid off and is the reason for our highly frequent high quality extraction. This method, born out of necessity, has also made us far better baristas as a result. 

Being sticklers for details, once we revisited factors such as bean quality and age, water quality, weather variations, and shot ratios, we thought we would visit the deep dark depths of pressure profiles to iron out the creases of our phantom excitable extraction (we use a brew ratio for our house espresso blend, Coleman’s Coffee Roasters, of 18-19 grams of coffee to 27-28 grams of extracted fluid. Our customers enjoy this and we as a business like our espresso to maintain espresso characteristics with full body, creamy texture and intensity)

Having experience with lever machines in the past we were able to compare low pressure ‘preinfusion’ brewing methods that we all experience when using a lever, to our standard nine bar shots of the discussed dual fuel machine, and their differing processes and results.

And so came, our mystery was uncovered! There was an undetected increase in our pressure, a rouge variable. We were running at just over 10 bars! We couldn’t explain why or how, but this was telling and insightful. We discovered the true importance of pressure in real time. To eradicate any questions around this resolution we run the machine like this for a full day, pulling shots with 10 bars with our standard brew ratio. The inconsistencies remained. We changed our ratios to meet this pressure difference and saw marked improvements, but they weren’t the shots that we were used to, or liked for that matter. The shots were still flatter, and lacking as much body with prominent bitter notes.

For an in depth break down of the importance of water pressure in your espresso extraction read James Hoffman’s (jimseven) post - It does take a few reads to process but the content to thorough and useful.

The small details have always been important to us but we are constantly being challenged by new investigations into brewing variables. This is a great thing in any industry we believe. This unfortunate situation has helped us stay on top of our game and has helped eradicate any complacency that began to show its head.

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