Coffee is prepared by the extraction of a complex array of organic molecules from the roasted bean, which has been ground into fine particulates. The extraction depends on temperature, water chemistry and also the accessible surface area of the coffee. Here we investigate whether variations in the production processes of single origin coffee beans affects the particle size distribution upon grinding. We find that the particle size distribution is independent of the bean origin and processing method. Furthermore, we elucidate the influence of bean temperature on particle size distribution, concluding that grinding cold results in a narrower particle size distribution, and reduced mean particle size. We anticipate these results will influence the production of coffee industrially, as well as contribute to how we store and use coffee daily. - Nature Article Here
I’ve been asked several times why the espresso here tastes different than many other places. I’ll just write a bit about espresso here and cover that question next time. Espresso is the product of a method of brewing, in which hot water is forced under pressure (about 9 atmospheres) through tightly packed coffee. The key to brewing espresso is obtaining optimum extraction. An all too common mistake is overextraction. In general, the good stuff in the coffee extracts first. If one continues to extract (ie. continues to let water pass through the grounds) after most of the pleasant compounds have been extracted, that person is committing the sin of overextraction. By passing to much water through the grounds you end up with a thin, bitter, watery drink. The “ideal” extraction for espresso is to get one ounce of espresso from 7 grams of grounds. The time it takes the water to penetrate and flow through the grounds must also be considered because if it takes to long brew that rich, creamy, flavorful, one ounce shot, you would be overextracting on a time basis – as the water has been in contact with the grounds for to long. Vice a versa with underextraction. The “ideal” extractiong time for a shot is 25 seconds. Some like a shot pulled a little longer to mellow it a little (a lungo, or long shot) and some like the shot pulled shorter for a very small and intense shot (a ristretto, or short). Espresso originated and evolved in Italy thus much of the espresso jargon is Italian or relates to Italy. I’ll talk about the roast degree and bean blends with respect to espresso next time.
In my explanation of why Muggswigz coffee has grounds at the bottom of the cup, I am describing some different brewing methods. Last week I wrote about three methods of brewing coffee; Middle Eastern (aka. Turkish or Greek), concentrate brewing, and percolating. In this issue, I'm going to write about vacuum brewing, drip brewing, and French press (aka. plunger press) brewing.
Vacuum brewing uses an elegant looking device that consists of two glass globes that fit together with an air-tight seal. Either in one of the globes, or between the globes, is a filter to separate the grounds from the liquor. Ground coffee is placed in the upper globe, often on top of the filter, and enough water to brew the grounds is placed in the lower globe. The globes are then fitted together and the lower globe with the water is heated. The water in the lower globe begins to heat to a boil and as this causes the pressure in the lower globe to increase it forces the water up a tube connecting the globes and into the upper globe containing the grounds. Once all the water has made this air pressure induced trip, the apparatus is taken off the heat source. This allows the lower globe to cool down back to room temperature, decreasing the pressure in the lower globe and thus sucking the brewed coffee back down (through the filter) into the lower globe. The coffee is then poured out of the lower container and enjoyed. Well, perhaps not always enjoyed. Because while the vacuum brewer is a great visual, scientific, and romantic experience, it does not always produce the best cup. A great cup of coffee can be achieved with the vacuum brewer, but it has its downfalls. Firstly, the coffee is being extracted by water around 212F, while it should be extracted between 195F-205F. Secondly, their is very limited control over the extraction time (the time grounds are in contact with water). Some swear by this method and it is growing in popularity. Perhaps I need more training in the technique, but I've never had very much luck with vacuum brewing. If you want to try vacuum brewed coffee, I think you can find the brewers at more up-to-date houseware stores, and I think they my sell the bodum version at Starbucks, or if you ask nicely I'll loan you one of mine for a test run.
Autodrip! This is the most popular way to brew in the US. Drip brewing is simply pouring hot water over grounds in a filter and letting the brew drip out the bottom. Drip brewing is a very good way to brew and can give an excellent cup if the correct equipment is used. A primary issue with autodrip machines is that they don't brew at the right temperature! I have read that Bunn is one of the few companies who's machines are calibrated to extract at the right temperature. If one has a good autodrip machine or one decides to heat and pour the water themselves, the next issue to surmount is the filter. Paper filters can impart a taste on the coffee and also do not allow many of the coffee oils and organic compounds through. A good gold-plated reusable filter (we do carry some) is a great option for drip brewing. Provided you clean and rinse it well after each use, it will not impart a taste on the coffee, and they don't trap as much of the coffee's essence as a paper filter. Another slight drawback is that drip brewing, in general, does not give the operator much control over extraction time.
French-press brewing gives the operator complete control. While it may be more labor-intensive then autodrip, the brewing variables can be easily and directly controlled. Coarsely ground coffee is placed in the glass carafe, then water at the desired temperature is poured over the grounds and the top is placed on. When brewing is complete, the plunger (a mesh filter on a stick) is pressed down, pressing the grounds to the bottom and leaving the coffee liquor on top to be poured off. The filter is not as tight as a paper filter and because of the larger pores, a coarser grind is required so the grounds are filtered out, and the plunger does not become almost impossible to press down. The mesh of the filter allows the coffee oils and all those delicious dissolved and undissolved solids through without a problem. Also, because a coarser grind is required, a longer steep time is required (because of the decreased surface area to volume ratio). A brew time between 3 to 6 minutes is common for French-pressing. This prolonged, direct contact of the grounds with the water allows for a more complete, more controllable, and even extraction. Unfortunately, even with the highest quality burr coffee grinder or mill, a coarse grind will still result in some very small coffee grounds. These grounds are not filtered by the French-press filter and thus end up in the cup. A cup of French-pressed coffee with be noticeably fuller, with much more body, and often with more flavor, it will often also have the tell-tale sediment at the bottom of the cup.
We're asked this very good question somewhat often here at Muggswigz. I personally love when I am asked this question because it gives me a chance to satisfy someone's curiosity about coffee and hopefully bring them to a greater appreciation of the beverage. I may also like it because it gives me a chance to brag. There are primarily six popular ways of brewing coffee (excluding espresso), each a permutation of the brewing variables - brewing temperature, introduction of the water to coffee, and separating the brewed liquor from the coffee grounds. These methods are Turkish brewing, concentrate brewing, percolating, vacuum brewing, drip brewing, and French Press brewing.
Middle Eastern, "Turkish" or "Greek" brewing involves boiling in water coffee that was ground into a very fine dust. Traditionally the coffee is often brewed (boiled) with large amounts of sugar, but it may be brewed without the sugar. Middle Easterners seem to like to add spice to their coffee, and their spice of choice is often cardamom. The coffee is not filtered from the liquor and one is left with a pungent, thick, and muddy brew. In the western world this method is more of an occasional indulgence as opposed to an everyday brew.
The next method, concentrate brewing, is very popular in Latin America and some other parts of the world, and is starting to make a commercial appearance in the US. In concentrate brewing, large amounts of coffee are brewed with little water to brew a concentrate, when one desires a cup of coffee, some of the concentrate is mixed with some hot water. The concentrate can either be brewed hot or cold. When brewing cold one must let the coffee sit for at least a day. This method results in a mild, light-bodied cup with little aroma, and often little acidity and a muted flavor.
Percolating, the procedure that involves continuous brewing of coffee grounds using boiling water which then turns to boiling coffee liquor brewing overextracted grounds. This method, while practical, is a disparaging disgrace to the coffee bean. Even brewing with boiling water is bad enough (coffee should be extracted at 195 - 205 degrees F), then actually boiling the liquor is asking for a thin, bitter, tarry cup. To add insult to a sufficient mangling, the grounds are continuously being overextracted. However, to show the variance of personal preference, I know of people that prefer this method. I can only imagine the preference can only stem from either positive memories associated with it, an acclimation to it over years of knowing no other, or the same phenomena that makes people stop to stare at a car wreck.
Coffee, like produce, is perishable. Not only is roasted coffee perishable, but how it is stored drastically affects how quickly it perishes. Beans kept properly maintain their freshness for about ten days. Coffee kept improperly can go bad within minutes. The first thing one can do to extend their coffee’s freshness life is to get a grinder. This is also one of the first things I often suggest to people when they ask me how they can improve their coffee at home. Get a grinder. Buy, borrow, find, construct, inherit, stumble upon, or ask nicely, but somehow acquire a grinder. Then make it a point to use said grinder (not store it away) and use it effectively (grind beans fresh for each brew).
Whole beans keep their freshness for days to weeks, grounds usually for minutes to days– this depends a lot on packaging too. Coffee beans go stale by oxidation (the same type of process that is used to process tea leaves into black tea). The rate of oxidization increases with oxygen concentration (whether is be in the form of air or water, therefore dry vacuum sealing and/or nitrogen flushing is preferred), the rate of oxidation is also increased, like most reactions, by increased temperature or light. So, staying practical, it is best to store whole coffee beans in an opaque airtight container in a cool dry place. We happen to package our retail bean purchases in just such a container!