There are many large and embarrassing gaps in my coffee knowledge, and coffee leaf rust is one of those. However, it seems that this is something that is having an increasing impact on producers and the industry so it seemed like time to do some research.
Before having a look at recent changes in global climate, rust resistant varieties and the conflict of crop vs cup we should probably start with exactly what coffee leaf rust is:
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The internet is quite talkative at the moment. The coffee sliver of the internet anyway. Lots of talk about seasonality, which is a good thing.
This does beg the question – how long is coffee good for? Green coffee I mean – we’re still arguing about roasted coffee’s shelf life and a great deal more time and money has been spent on that topic in the last 100 years.
If anything, and we are getting into the realm of personal opinion here, green coffee is trickier because green coffees don’t age the same way. Each lot is an individual little time bomb. As much as we can look after it as well as we can in storage/in roasteries – we are still working with an individual fuse whose approximate length was determined before the coffee left the producing country. (more…)
Back in 2006 I published a recommended reading list. Since that time my collection of books has (worryingly) increased so I thought I should probably update it. I could easily write a list of coffee books that one should avoid (having learned the hard way) but I suspect that would get me into rather a lot of trouble, so I shall leave that for now. I’ve broken it down into two parts and then down into sections, and have indicated which are nice to have, and which I would consider are essential on that subject.
I will try and keep this one updated – if you think I’ve missed something obvious then let me know. I haven’t recommended books I don’t own, so this means some books may be missing that you would expect to see here.
I had a brief moment to dig into a couple of books and was pleased to come across the following passage in Coffee: Recent Developments 
According to the owner of the stoneworks auction website, I was one of up to 3000 users watching or participating in the latest auction. It went on for 9 hours and you had to feel very, very sorry for the Japanese who would have started bidding at 10pm and finished around 7am. (though you suspect they probably had access to sufficient caffeine)
I am not going to go through who won what (it is there on the website still) but there are a couple of things about this auction process, about the success of this farm, that I want to write a little about and get some feedback on from the community.
First of all I was quite surprised that the Petersons decided to auction off so many small individual lots. The high prices achieved in the past were a function (in my mind) of both quality and scarcity. I don’t debate the mesmerising cup this coffee is capable of producing, but I don’t think that it would have reached $130/lb last year if there had been 10 times the volume available. Granted, the small individually processed batches have drive the price up on the top lots to similar heights but this then leaves the issue of how to communicate the difference between Stumptown and Sweet Maria’s $105.25 lot and a $6 lot. What key areas would the consumer respond to and be willing to massively increase their spend for?
The variation in price also implies a variation in quality. This is not a criticism of the farm – no farmer in the world is going to claim they produce nothing but exceptional coffee. I do worry, however, that there is potential to damage the brand. (and I have no doubt that it is a brand now) I have seen more extreme examples of this in other super-farms such as Daterra. Daterra is a cutting edge farm, capable of producing stellar coffee, and the research they are involved in is invaluable. I know they did a great deal of work on tracing aroma in the cup back to the crop with Illy and I hope eventually some of that research will see the light of day. What surprises me is that they have not distinguished very strongly between their best lots (like the reserve) and then other lots which don’t taste as good. I have seen several roasters proudly claiming the Daterra component of their blend without specifying which one it was and the coffee not tasting great. I thought the idea of the Esmeralda Especial worked well, but was still being muddied by some people so if anything I would have thought they would have distinguished lots even more aggressively.
I feel very strongly that for us to really move forward in speciality coffee we must consistently deliver on our promises to the consumer. Asking them to pay a high price for a cup promises that it will be worth it, and making proud boasts about the coffees we use promises that they will taste something that will be starkly different, discoverable and satisfying. Will every single roast of the Esmeralda be great this year from all the different companies? Does a new, but interested consumer, tasting an average cup of Esmeralda leave them very confused about the prices of the higher lots? Do we risk looking exclusive rather than inclusive to those teetering on the edge of becoming interested and excited about great coffee?
My other thought on the success of the farm has been the double edged sword of the visibility of the Geisha varietal used. I travelled a little bit in Costa Rica last year and every farm I visited had at least a little Geisha planted. Some were more cautious than others in the space they were giving over to the gamble. In three or four years will we see a sudden flood of Geisha on the market (which will immediately drop its desirability) and will it be any good. A while ago I dug through my coffee text books to see if I could find any references to the varietal. I found very little except for a small study carried out abotu 40 years ago in Costa Rica comparing the success of various varietals of which Geisha was won. It lost out primarily because of its lack of yield – less of a problem if you have quality and scarcity on your side, but with lots of people suddenly producing lower yields from their farms scarcity becomes void. No notes are made in the study about increased cup quality, but that study could still easily be dismissed as techniques have moved on and you could also argue that Costa Rica’s quest for yield held it back as an origin producing distinct and amazing coffees until the more recent micro-mill revolution that we are seeing signs of. (if people want me to dig up the study I can do)
On this subject I am very happy to concede I might be wrong. I haven’t spent enough time at origin to feel completely confidant in the above statements, and if Peter or Geoff or anyone else who has spent a lot of time at origin are reading and want to correct me I would be very grateful. I really just want to learn more, and hope that we aren’t all debated-out on this issue which covers just about all of the coffee industry.
This article is a simplified version of what was researched and written for the attempted coffeed study group. Sadly that project didn’t take off – however I am grateful to people like Andy Schecter and Jim Schulman for publishing the papers they wrote regardless. The article doesn’t focus much on cup quality and the specific effects of the process – more on the process itself.
The Wet Process
The primary goal of the wet process is to remove the sticky layer of mucilage that surrounds the beans and parchment before the coffee is dried. The practise stems from a simple goal of improved consistency and reduced defects in a lot. When this layer is removed there is a lowered chance of problems and flaws in the coffee. However it should be made clear that this does not mean that it will be of a higher quality as that is both subjective and also needs to be balanced by what characteristics are desired from the coffee. As the process uses up a lot of water it is only the higher grades of cherries that go through this process – in terms of ripeness or varietal.
There isn’t much on the history of the wet process available. The earliest printed source I have is Ukers, and the process of loosening the bean from its “closely adhering saccharine coat” is documented in reasonable detail.1 I’ve heard various different things about its origin, and Costa Rica is the most commonly quoted country to me (though I currently have nothing solid to back this up).
A coffee bean after pulping, still coated in the mucilageThe mucilage layer is primarily carbohydrates – a variety of simple and complex, long chain sugars2 , and is between 0.5mm to 2mm thick3. The washing process, broadly speaking, is considered complete once the layer easily comes free from the parchment. The simplest test is to take some of the beans and rub them – if they retain a slimy texture then they are not ready, though if the mucilage easily comes free in the hand then they are ready to be removed, rinsed and dried.
The carbohydrates that we want to break down are celluloses keeping the cell walls together, the most common of these in coffee is also found in many other fruits: Pectins.
Pectins
The Structure of PectinThe key to successful fermentation of coffee is balance of the methods of breaking the pectin down: bacteria and yeasts.
Bacteria can produce enzymes like pectinase and pectase that are specific biological scissors that break the pectin down. However some research done claims that the most commonly found bacteria in the process do not produce the right kind of enzymes to effectively break down the mucilage. 4
Yeasts break down the pectins too, but the byproducts of those reactions are typically ethanol and lactic acid. In the right conditions the balance is right and the mucilage is broken down quickly with no negative characteristics being developed.
The source of the enzymes is even more of a mixture than that – there are plenty already within the cells of the fruit. These enzymes are gradually softening the fruit as it ripens. Once the bean is pulped they become much more active, due to the oxygen and the presence of other bacteria.
Of the three sources of enzymes it is important to note that yeasts prefer oxygen free conditions, whilst the bacteria are more effective with oxygen around. For this reason it is important not to let water tanks stagnate, as then the yeasts take over causing negative flavours. Different types of fermentation – open, water covered or a mixture – will have a different balance of reactions for this reason, creating a very different cup profile.
Once pectin breaks up, in an environment with sufficient calcium it can start to gel – this is useful if you are making jam for example. This also explains a rather amusing test of fermentation done in some parts of Costa Rica – a stick is put upright into the tank and if it stays upright (held by the gelatinous water) then the fermentation is done.
There are various factors that affect the balance and speed of fermentation:
Temperature
This is the key variable in fermentation, and is the key variable dictating the time it takes. Enzymatic reactions are directly linked to temperature so at higher altitudes the process takes longer as the ambient temperature is usually lower. To increase the speed of fermentation it is possible to preheat the water in various ways before the cherries arrive at the station to be pulped, but I am not sure how common this is.
Acidity and pH
Again sources here seem to disagree about whether pH should be close to neutral or quite acidic5”. It can often get down to a pH of 4.5 towards the end of fermentation – it is worth noting here again the pH is a logarithmic scale so a pH of 5 is 10 times more acidic than a pH of 6, and 100 times more acidic than a pH of 7. At lower pH the yeasts do better than the bacteria, though I’ve read that low pH can stall a fermentation.
Work was done in Nicaragua on monitoring pH to see if it was an accurate predictor/indicator of the state of fermentation6 The sharp drop to around ph 4.5 near the end of the fermentation was also matched by an increase in lactic acid and ethanol implying that the yeasts had taken over the bulk of the breakdown of the carbohydrates at this point, though it seems unlikely that they were the cause. More likely the products created by the bacterial and natural enzymes caused a drop in pH and also slowed down their own reactions.
pH during fermentation in NicaraguaThere aren’t many other studies widely published using pH as a tracker, though I’d be interested to see more.
Part 2 will cover more about specific cup qualities linked to the wet process, including the generation of off flavours like vinegar and onion. Any questions, corrections or things that don’t make sense then please leave a comment (I lost a few of my original papers since I started the original paper).
Footnotes: