To be able to decide on a brew method for a certain coffee, and more in particular on the filtration media( paper, metal, cloth, etc.), we first need to understand what it is in coffee we will be working with as well as the physical nature of these constituent parts.
Then we need to understand how these function and how they get enhanced or separated in the brew.
The two contributors in a coffees profile that change between brew methods are the Brew Colloids and Acids.
These two major effectors are what you will be manipulating in order to bring out the best in your brew. The focus today will be on Brew Colloids and the filter materials that alter them.
Let’s get started.
Firstly-Brew Colloids are formed when Fatty Oils and Sediment combine.
-Fatty oils are the undissolved liquid materials.
-Sediment is the undissolved solid material.
Interestingly, Coffee oil is composed of various triglycerides and is actually similar in composition to our everyday butter and cottonseed oil. The fatty oils in coffee play an incredibly important role, albeit somewhat subtle, in the overall flavour profile of a coffee. Besides playing a crucial role in mouthfeel creation, the oils carry other flavour compounds.
Sediment comes from two sources. Firstly, a small amount of bean fiber washes off the surface of the coffee particles in the brewing process and will remain suspended in the brew. Secondly, the remaining undissolved solid materials are proteins.
Ok….. lets move on.
Brew Colloids have two properties. They are absorbing and adsorbing.
[Visualize the combination of Fatty oils and Sediment- like little blobs ☺]
They are absorbing when layers of aromatic compounds cling to it,holding it in the brew until the coffee is swallowed. (This is where retro-nasal aroma perception comes from.)These brew colloids will break up when swallowed and the volatile molecules of aroma reach the olfactory receptors in the nose, where aroma is perceived as taste(This mechanic is known as retro-diffusion).
They are adsorbing when they act as a buffering agent in a brew to produce a less acidic cup. This can be detected both through taste and measuring the pH. As an analogy, imagine that the acids are pins, and the Brew Colloids are marshmallows. Put a marshmallow on the tip of a pin and you won’t feel the pinprick.
Side note: One major purpose of Traditional Cupping is to greatly enhance Brew Colloid formation, so that the broader spectrum of a coffees flavour can be perceived.[Keep an eye open for my future blog on Cupping and flavour analysis.]
So how can we apply this information in our everyday brews at home or at the office?
Lets take a look at the most popular filters of our brew methods- paper, metal and cloth.
Paper holds a huge amount of Fatty oils as well as Sediment. The cup in this regard will generally be lighter bodied and have a super clean texture. The adsorbing effect would be minimized(your acid perception would increase). This is especially great for East African or Central American coffees, washed coffees that have a high quality and prominent acidity potential.
Metal allows large amounts of both Fatty Oils and Sediment into the cup, depending on the porosity of the filter and dynamic of the brewing process, of course. In this regard, you can look for heightened body,texture(mouthfeel) and aroma perception(because the absorbing effect has been enhanced). This is especially great for South American, some Central American and Asia Pacific coffees.( Although this type of filtration allows for a great deal more versatility.)Be warned that using metal filters will allow some degree of micro-fines(tiny bean fibers)in your cup. This typically over extracts and creates astringency and bitterness.
Cloth seems to allow a fair amount of oil through, with no visible or perceptible sediment. The cup is actually super clean but has some decent body (from the oils) and a moderately high level of aromatics because of this. Complex coffees with a good balance between acid and body-quality potential work really well here. The decision making process on coffee choice here seems to be broader, and depends on the overall character of the coffee.
So the next time you purchase coffee- think about how you are most likely going to brew it. As you can see, the type filter alters the brew in a serious way.
Next time I will talk about the effect of the brewing dynamic, grind size and water temperature.
[P.S.-I prefer Paper filtered East African coffees, where the adsorbing and absorbing mechanic has been negated and the acidity potential has been given room to shine. But thats just me. ☺]
Until next time.
Espresso Coffee: The Science of Quality(http://www.amazon.com/Espresso-Coffee-Second-Edition-Science/dp/0123703719/ref=sr_1_1?ie=UTF8&qid=1405444525&sr=8-1&keywords=the+science+of+espresso)