Chemical Engineering 101: Optimized Extraction Of Aromatic Organic Compounds From Thermally Processed Herbal Rubiaceae Seeds (Commonly Referred To As “HOW TO MAKE GREAT COFFEE”)
WHAT MAKES GREAT COFFEE?
When we think of great coffee, we think of a rich tasting brew with a deep color, fragrant aroma and full flavor rich in aromatics and some sweetness, with little bitterness or sourness. We generally think of coffee which tastes as good as it smells out of the bag.
Specific qualities of great coffee are generally:
SO WHERE DO WE START?
THE BASICS, #1 INGREDIENTS
The first things to look at are the raw ingredients used to make coffee. Coffee is a natural product and it contains many delicate compounds which make up its aroma, taste, flavors and mouth feel. Some of these compounds are volatile (they can evaporate out of the coffee as it stands exposed to the air) and some will break down when they are exposed to heat, light (especially sunlight) or moisture (water, humidity in the air, or condensation). Coffee will also pick up flavors and tastes from its surroundings.
To get the best most flavorful knock-your-socks-off cup of coffee that tastes as good as it smells, you must start with quality coffee beans and you must store them appropriately so as to maximize the delicious life of the coffee and prevent it from going stale for as long as possible.
So here are the basics for managing your coffee supply:
The next thing to look at is the equipment used to make your coffee. Everything that touches your coffee should be spotlessly clean. Think about if you were ordering coffee at a restaurant or coffee house. You would not want to see old stained coffee pots and coffeemakers full of scale and residue…yuck!
Another critical piece of your brewing system which makes contact with the coffee and greatly influences its quality is the filter. A good filter will produce a clean tasting flavorful cup of delicious coffee, while a bad filter can produce a bland cup of coffee with a cardboard like flavor. So always use good quality filters. This means:
Have you heard this statement before? “I like how coffee smells, but I don’t like how it tastes”
So why is it that coffee which starts out smelling heavenly out of the bag ends up not tasting so great when it’s in your cup? What happened to all those great flavors and aromas?
The answer to this has to do with the chemistry of the coffee brewing process. Roasted coffee beans contain many compounds (chemicals) which make up the characteristics of the qualities of the coffee. Some of these compounds have great aromas and flavors. Some are sweet. Some make the coffee feel smooth when you drink it. But others are bitter, or sour. Some taste like cardboard and some make your teeth feel squeaky when you drink them. And then there is caffeine which is also a compound extracted from coffee. Caffeine tastes bitter at high concentrations, but in coffee there is not enough caffeine to add any flavor.
The balance of flavors in the cup of coffee you drink is determined by the brewing process used to extract out or dissolve out the compounds from the coffee beans and get them into your cup. Brewing is a chemical process known as “extraction” which removes compounds from one substance (coffee beans) by using a solvent (water). The purpose of the brewing process is to extract out the greatest amount of the good compounds (flavors, aromas, sweetness, smoothness) and leave behind as many of the bad compounds (sourness, bitterness, off flavors) as possible.
Hot water works much faster than cold water in extracting out compounds from solid materials, especially compounds which contain oil. Cold water will work too, but it will take a long time, just like making ice tea using a pitcher of cold water and tea bags.
For brewing coffee, the typical brewing process is to grind the beans and then pass hot water over them to extract out the desired compounds. The coffee is ground to increase its surface area. More surface area means more contact with the hot water and that means more compounds are extracted. The coffee/water mixture is then filtered to separate out the solid parts (the coffee grounds), and the result is the delicious cup of coffee you can drink.
It might sound like more extraction is better because it means more flavor, but this is not the case since the extraction is taking out the good and bad compounds from the coffee and dissolving them into the coffee you will drink. More extraction means more bad compounds which can overpower the good compounds and result in a very bitter flavorless cup of coffee. The trick is to extract out the right balance of compounds mostly good ones and a minimum of bad ones. There is a point in the extraction process where the quality of the brewed coffee is optimized (the best you will get). Too little or too much extraction will make less than great coffee.
In general coffee that is under extracted (too little extraction of compounds out of the coffee) has a weak flavor and tastes sour. And coffee that is over extracted (too much extraction of compounds out of the coffee) has a strong but bitter flavor and may cause your teeth to feel squeaky.
The extraction is determined by the following factors:
There is an optimal point for all these factors where the best coffee is produced. All of these factors need to be considered to get to this point. Let’s look at each one.
THE TYPE OF BREWING METHOD USED
Making coffee is a type of chemical process known as extraction where compounds in one material (ground coffee beans) are dissolved out into a liquid solvent (water). There are different methods for doing this extraction. Some use electronic systems to control the extraction and others are manual which allow the process to be varied but also requires someone to perform and closely monitor the process.
The most common electric coffee making systems are drip coffee makers and percolator systems. There also espresso making systems which use a different process where hot water under pressure is forced through the coffee beans in a very short time.
Drip coffee makers are the most common type of coffee making systems. In this system, water is heated to a set temperature and then the hot water is showered over the ground coffee which is in a basket lined with either a paper filter or metal screen. The water passes over and through the ground coffee and drips out the bottom of the basket into a coffee pot. The coffee pot is either glass or it can be stainless steel. Coffee makers with glass coffee pots typically have a hot plate under the pot to keep the brewed coffee warm. Stainless steel coffee pots are typically thermal type carafes which keep the brewed coffee warm through their insulating properties, much like a Thermos bottle where there are 2 walls of the bottle with air space in between to reduce the conduction of heat out of the pot. Of the two types of coffee pots, stainless steel thermal carafes are more expensive but they are able to maintain coffee for a longer time without losing any flavor. The heated glass pots will tend to drive off the flavors and aromas of the coffee as more heat is added after brewing. Many restaurants use drip coffee making systems, as do coffee shops since they are reliable, consistent, economical, and easy to clean.
Percolators used to be the standard coffee making systems before drip became more popular but they are still used. Usually at large gatherings you see coffee urns which are large percolating systems. In a percolator, the coarse ground coffee is placed into a basket at the top of the coffee pot. Water is added to the bottom. The percolator heats water to boiling and then uses the pressure created by the steam to force the hot water up through a tube and sprays it over the basket where it comes into contact with the ground coffee. The water is recycled many times until the desired strength of the coffee is reached. For electric systems, the percolator will automatically turn off at a preset time. For stove top systems, the person making the coffee must keep track of the time and turn off the stove when the coffee is done. This method is different from drip coffee where the water passes through the coffee only one time. Percolator systems are used for large gatherings like conventions, weddings, church events etc. because you can make a large amount of coffee quickly without needing to watch over it and the pot keeps it hot.
Espresso requires a specialized coffee making system where hot water under pressure is forced through finely ground coffee to extract out the maximum amount of flavor in a very short time.
There are also the pod type coffee makers. These systems are fully automatic and do not allow for any variation on the brewing process beyond the settings on the user panel (i.e. some allow for “Strong” vs. “Regular”). The coffee is contained in a sealed plastic cup with a filter at the bottom. Therefore the amount of coffee used is set by the supplier and cannot be varied. The water temperature and brew time are automatically controlled by the machine. So the only part of the brewing process that the person making the coffee can control is the type of water used to make the coffee.
Popular manual methods for making coffee include French press and pour-over. The French press is a cylindrical glass coffee pot with a stainless steel plunger with a screen at the bottom. The ground coffee and hot water are added to the pot and then the plunger/screen are placed at the top of the pot. After a set amount of time, the person making the coffee presses the plunger down and the screen slides down the pot and strains out and compresses the ground coffee at the bottom of the pot. The brewed coffee above the screen is then poured out into a cup to drink. People like this method because it results in a more full flavored and full bodied coffee than drip coffee. Paper filters used in drip coffee tend to remove some of oils in coffee which contain the flavors and aromas of the coffee beans.
The Pour-over is much like a manual version of drip coffee. The ground coffee is placed in a screen or paper or cloth filter in a funnel which is placed over the coffee pot. The person making the coffee boils the water in a kettle and then lets it sit for a minute before pouring the hot water slowly over the ground coffee in a circular motion so as to wet all the ground coffee evenly. The water passes over and through the ground coffee and then drips out the bottom of the funnel into the coffee pot. This method requires that the person carefully pours the hot water at a controlled rate so all of the ground coffee is in contact with the hot water for a set amount of time. Specialty coffee shops use this method to produce very flavorful coffees.
Moka pot is a two-chamber pot used on the stovetop, typically used in Europe and Latin America, for making espresso-like coffee. The Moka pot uses stem to brew the coffee by boiling water in the lower chamber and then passing the steam pressurized hot water through the coffee basket and then into the top collection chamber.
This pot uses steam to pressurize the hot brewing water, which allows for higher brewing and extracting temperatures. This is similar to the espresso brewing process, however the pressure is lower than pressures used during espresso brewing. The result is a bolder more intense flavorful coffee than drip brewed coffee, somewhere between drip and espresso brew.
TURKISH & GREEK COFFEE
Turkish coffee is made by taking very finely ground coffee beans and boiling them in a special pot (with a narrow neck and a long handle) on top of the stove. After a set amount of time, the heat is removed and the ground coffee sinks to the bottom of the pot. The brewed coffee is poured off the top of the pot. It still contains suspended solids after it is poured into the cup. This sinks to the bottom and laves a layer of sediment in the cup.
Each of these methods noted above requires the coffee beans to be ground to a specific size range to achieve the best results.
GRIND OF THE COFFEE
Each brewing method works best with a specific grind size. The rule is:
The finer the grind of the coffee, the greater the extraction of compounds. If the coffee is ground too fine for the brewing method, the brewed coffee will be too strong and bitter and might make your mouth squeaky. You will end up with ground coffee that smells great before you brew it but does not taste great after you brew it.
If the ground coffee is too coarse, the coffee will be too weak and have too little flavor, aroma and body. Once again you will end up with ground coffee that smells great before you brew it but does not taste great after you brew it.
The method of grinding is important as it is important for all the ground coffee to be uniform in size. If there is variation in the size of the ground coffee (some pieces are big and some are very small) then the quality of the brewed coffee will not be consistent as some of the ground coffee is over extracted, some is perfectly extracted and some is under extracted.
The best way to get a grind which is uniform is size is to use what is known as a burr grinder. This is the type of coffee grinder used in coffee shops and supermarkets. It works by crushing the coffee beans between two disks called burrs. The distance between the burrs is adjustable and this allows you to select the size of the grind you want. The ground coffee that comes out of this type of coffee grinder is very uniform in size. The problem with these types of coffee grinders is that they tend to be more expensive than the lower cost blade grinders.
Blade grinders work by breaking up the coffee beans using a spinning blade (like a food processor or blender). These types of grinders are inexpensive but they produce ground coffee which is not uniform in size (some pieces are big and some are small). Also, the high speed action of a blade grinder can heat up the coffee and cause it to lose some of its aroma and flavor oils. These are less expensive but they are not perfect.
Another problem is that you cannot select the size of the ground coffee. You must judge this by eye as you grind it. If you do use a blade type grinder, it is recommended that you pulse it on for a few seconds and then let the ground coffee rest for a few seconds, then tap the grinder to redistribute the coffee and then pulse again. This increases the uniformity of the final grind and reduces the amount of heating of the ground coffee. For drip or pour-over coffee, grind the coffee beans for a total of 15-20 seconds. For French press or percolated coffee, grind the beans for 10-12 seconds
QUALITY OF WATER
Since water is the solvent used to extract the compounds from the coffee and water is 98% of the coffee you are drinking, the quality of the water used for making coffee is very important to the quality of the coffee you make.
Not all water is the same. There are many different sources of water and each source contains different chemicals which change the flavors and qualities of the water.
Distilled water is produced by boiling water and condensing the steam back to liquid. Distilled water is ultra-pure and contains no dissolved chemicals.
Tap water is what comes out of the faucet. This water contains different minerals like calcium and magnesium, depending on where the water comes from. It also contains added chemicals like fluoride (for the health of your teeth) and chlorine (for killing germs and bacteria).
There is bottled water which contains minerals similar to tap water but without the chlorine and fluoride.
And then there is treated water such as tap water you filter in your home or city water which is processed through a reverse osmosis (RO) system in a restaurant. The filter or RO system removes sediment, bacteria, chlorine and other chemicals which give the water a bad taste.
For the purpose of making coffee, distilled water is not acceptable. Some mineral content is needed in the water or else the coffee will taste flat and lacking in flavor.
Tap water is generally not the best choice because the chlorine will add undesirable flavors to the coffee. Some tap water may also contain minerals such as gypsum (calcium sulfate) which add an undesirable flavor (like sulfur – rotten eggs) to the water and to the coffee.
The best choice for water to use for making great coffee is water that tastes great to drink. The ideal type of water to use for brewing coffee contains some mineral content but does not contain any compounds which produce bad flavors (like chlorine or rotten eggs).
Good choices include bottled drinking water (spring water or purified drinking water, not distilled water) or tap water which has been filtered or conditioned using a purification system designed for drinking water.
Softened water is not good for making coffee as most of the beneficial minerals such as calcium have been replaced with sodium, which will result in a duller flavor and add to your intake of sodium which many people are trying to limit.
Most coffee shops use treated tap water. This enables them to have control of the quality and consistency of the water they use. Bottled drinking water is fine as well. Or if you live in an area where the quality of the local water supply is very good (such as ground water from deep wells or aquifers) and does not need treatment with chemicals, then feel free to try this out for brewing coffee.
The bottom line is that if the water does not taste good to drink by itself, then it will not make good coffee.
Just one thing to keep in mind with ground water (such as well water) is that it tends to contain higher levels of minerals such as calcium and magnesium which will leave deposits (scale) behind in your coffee making equipment at a faster rate than water with lower mineral content. This means that you will need to clean and descale your equipment more frequently. Soaking your equipment in a vinegar/water solution for an hour or so will generally remove the scale from the surfaces.
TEMPERATURE OF THE WATER
The temperature of the water when it comes in contact with the coffee has a big effect on the extraction. Different compounds in coffee (and there are tons of them) are soluble at different rates depending on the temperature of the water. As the water gets hotter, the rate at which compounds can dissolve out of the coffee and into the water gets faster (think about dissolving sugar in hot water vs. cold water). Also as the water gets hotter, it is easier to remove more of the water resistant (oily) chemicals from the coffee. This is why it is much faster to make coffee and tea using hot water than using cold.
The problem is that hotter is not always better. Some of the compounds taste bitter or taste “off” (i.e. taste bad, such as tasting like cardboard) and you want to limit the dissolution of these into the water but you still want to maximize the dissolution of the good chemicals (the flavors and aromas and sweetness). If the water is too hot, you will end up with coffee with a lot of extra flavors and bitterness which may cover up the good flavors and qualities. You will get coffee that smells great but does not taste too good.
If the water is colder, the rate of dissolution will be slower. This means there will be less bitterness, but there will also be less flavor as some of the important compounds may not be dissolved into the water in sufficient quantities to give the coffee the qualities you want. Once again you will get coffee that smells great but does not taste too good.
The trick is that you need to have water that is sufficiently hot but not too hot so that you will extract out the exact balance of compounds needed to give you the qualities of coffee you want; smooth, full of flavor and rich aromas with some sweetness and little bitterness. To achieve this when brewing hot coffee, the ideal water temperature is just slightly below boiling. This is 200-205 degrees F (93.3-96.1 degrees C).
If you are using an electric coffee maker (drip, pod or percolator), the temperature is automatically controlled for you, so you do not need to worry about this.
If you are using a manual brewing method like French press or pour-over, the best way to get the correct water temperature is to bring the water to a boil in the kettle, then turn off the heat and let it sit for 1 minute before pouring it over the coffee.
AMOUNT OF TIME THE COFFEE IS IN CONTACT WITH THE WATER
The next big factor which determines the amount of extraction of compounds from the coffee is the amount of time the water is in contact with the coffee. Since each of the compounds can dissolve out of the coffee at different rates, some will be completely dissolved quickly and other will take longer.
The amount of time that the water stays in contact with the coffee will determine how much of each compound is dissolved out or extracted out into the coffee. Ideally you want the good compounds (flavors, aromas, sweetness, smoothness) to be completely dissolved out and the bad ones (sourness, bitterness, astringent quality – makes your mouth squeaky) to be left behind as much as possible.
If the coffee is in contact with the hot water for a time that is too short, not enough of the good compounds will be dissolved out and the coffee will be bland and not have the full flavor and aroma it should have. You will get coffee that smells great but does not taste too good.
If the coffee is in contact with the water for a time that is too long, too many of the bad compounds will be dissolved out and the coffee will be too bitter and may have off flavors (stale, cardboard, etc.). Once again you will get coffee that smells great but does not taste too good.
The ideal time for the hot water to be in contact with the coffee is 4 – 5 minutes. If you are using an electric brewing system (drip, pod or percolator) and you have the correct grind size, the brewing system will pass the water through the coffee for the correct amount of time. If you are using a manual brewing system like French press or pour-over, you will need to manually control the amount of time the water is in contact with the coffee. For French press this means setting a timer and then removing the coffee from the pot (otherwise the extraction will continue for too long). And for pour-over this means having a timer and controlling the rate at which you pour the water over the coffee.
THE RATIO OF COFFEE TO WATER (HOW MUCH OF EACH)
The amount of ground coffee compared to the amount of water used to brew coffee is critical for getting the right extraction. If the amount of ground coffee is too little for the amount of water, there will be too little of the good compounds dissolved out into the brewed coffee. The bad compounds (bitterness, off flavors and astringency – makes your mouth feel squeaky) will be more apparent in the brewed coffee. You will get coffee that smells great but does not taste too good.
If the amount of ground coffee is too much for the amount of water, the brewed coffee will not achieve the full flavor, but the coffee may be very bitter, as the water will not be able to completely dissolve or extract out all of the good compounds from the ground coffee in the right proportion to the bad compounds. Once again you will get coffee that smells great but does not taste too good.
You need to have the right ratio of ground coffee to water in order to provide right balance of compounds extracted or dissolved out into the brewed coffee. This perfect ratio is generally 2 Tablespoons of ground coffee to 6 ounces of water. This can be varied slightly but not too much. Always read the directions on the coffee package or start with this ratio of 2 Tablespoons ground coffee to 6 ounces water when first brewing a new type of coffee and then try experimenting by changing the amounts in small quantities up and down and see what the results are.
QUICK CHECKLIST – DO’S AND DON’TS OF MAKING GREAT COFFEE
Do Make Sure You:
Don’t Make These Common Mistakes:
That’s it! If you follow these logical steps you too can brew incredibly rich flavorful coffee without spending a lot of money on fancy equipment or taking lots of time experimenting with different recipes.
More information at: https://www.ibrewthebestcoffee.com/
© 2022 Diogenes Publishing LLC
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