Sunday, 18 November 2012

Flexing The Brewing Control Chart (Part 1)

Suppose you boil an egg for 30 minutes and it comes out all runny-yolked and perfect for dunking your toast soldiers. That shouldn't happen, as we know. A runny egg is 4.5 minutes (in my kitchen, anyway). Perhaps it could happen though. Perhaps the egg was boiled at very high altitude... 6000 metres... where water boils at lower temperatures. So with a different perspective we can perhaps make things work that simply shouldn't. 

Some of the tastiest coffees I've ever brewed should have been awful. They should not have been good according to current brewing standards. I want to explore how this could be.

I'm an advocate of Controlled Brewing. Using specific weights and measures, temperatures, times etc, and (importantly) taking a reading of the coffee's concentration (TDS) and extraction yield % after brewing. Why? I guess it goes back to my previous career in business consulting & finance, where we adhered to "what gets measured gets managed". So I control the brew, steer it into the parking space... my target TDS & extraction. 

What is the target though? Well, I've always supported Gold Cup standards so I aim for the middle of the Brewing Control Chart at first (with a new coffee), then tweak to make it stronger/weaker/extract more/less... adjusting according to taste. Standard stuff that I often say more people should do. 

But recently I've (initially accidentally) brewed coffees that measured substantially outside Gold Cup and yet tasted so good that the memory of drinking them makes me long for a cup some weeks later. 

So this raises many questions for me, such as: 
What has changed recently?
Is this a peculiarity of the coffees I've been using? 
Is it just my tasting/sensory skills being terrible? 
Does this mean the rules of Gold Cup are somehow wrong or incomplete? 
What other factors might be at play here? 

I'm not a scientist. I can't analyse the coffee's chemical composition and identify possible causes for the great flavour... high levels of certain compounds, acids, oils etc. 

I'm not a Q Grader with the cupping skills to pinpoint the specific olfactory and gustatory characteristics that make these coffees so great. 

So all I can do is hypothesise, and hopefully test my hypotheses with a little unscientific rigour. 

The first of my hypotheses is that the 'ideal' target TDS and extraction yield is not a static box as depicted on the Brewing Control Chart. TDS between 1.15 and 1.45% is not the ideal range... or rather it is only the ideal range in certain circumstances. The same applies to 18-22% extraction yield. Having ranges is ok... the box.. but the box must be flexed up or down both axes. So the ideal range may be a TDS of 1.45 to 1.65%, and extraction yield of, say, 20-24%. 
These are the sort of ranges that have produced some stunning brews for me. But likewise the ideal range might also be LOWER than the Gold Cup range.
The second part of my hypothesis is that the parameter which makes this possible, which defines how far the box needs to be flexed, is brew water chemistry. 

Consider this. Flexing the box already happens. The SCAA box is lower on the TDS axis than SCAE, which in turn is lower than the Nordic range. 
Why might that be? We assume it is just different taste preferences in each region, but I wonder whether that assumption has ever been adequately tested. Perhaps the underlying reality is that the different water in each part of the world affects the brewing process so differently that it shifts the box... it causes people in Norway, for example, to prefer a higher TDS. If you took that Norwegian on holiday to Seatle they may find they prefer their coffee brewed to a weaker TDS. 

I know I'm probably not convincing anyone with these maybes, perhapses and unproven hypotheses. I do want to support my hypotheses somehow though, so I'm currently collecting water from various parts of the UK, each with different chemical compositions. I'll use these different waters to brew coffees with various levels of TDS and extraction yield.  I will attempt to gather a panel of tasters to rate each one. In this way it might be possible to identify and measure any potential correlation between water chemistry and preferred position of 'the box' (i.e. TDS and Ext%). I'm looking for specific factors beyond just TDS playing a part. The calcium hardness, the carbonate hardness (alkilinity), and the pH... along with any other ingredients such as polyphosphates. 

I aim to conduct tests and post the results in the forthcoming weeks (time permitting) regardless of whether they suggest my hypotheses are right or wrong. I have no issues with being wrong. "Only through mistakes can there be discovery or progress."


  1. So informative and interesting post sharing by you... Coffee - UK

  2. Nice post - Agreed that is is very difficult to merely tie things down to fixed paramaters as there are just so many that may actually be out of your control. Though the guidelines are avaialble to give you a good starting point fom which to experiment. We did some playing around using the same water parameters, brewing method and merely changing the roast and bean. Not suprising completely different flavours with the same water. Further looking into the roasting and cupping to check roast flavour,they used their own tap water for the qualification which was higher than the SCAE recommendation and on at last one roast higher water values gave the best flavour. Also great to actually review destilled water - there is the common statement that it over extracts - try it and you may actually find extraction is under extracted, but there is a high extraction of acidics which may not give the greatest of flavours - which is where I guess the term is implying over extraction of particular components rather than a balanced extraction.

  3. That is really nice and helpful information that can helps us a lot, great post!