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Extraction and Coffee Brewing – A Guide to Coffee Perfection

Many different factors can influence the rate and extent to which coffee is extracted. Factors such as grind size, coffee to water ratio, and brew temperature are all interlinked and together are responsible for coffee extraction. When one factor is adjusted, all others are affected. This is why you need to follow that-recipe-you-found-on-the-Internet religiously.

Brewed Chemex Coffee

This article will discuss some of those main variables which govern how strong or weak a brewed cup of coffee is, as well as whether or not a brewed coffee is over or under extracted in a bit more detail.

Our intent is to give you enough information, so that you understand how changing brewing parameters will affect your final cup. We want you to be able to change that-recipe-you-found-on-the-Internet, and make it better.

What Is Extraction?

Extraction is the process that pulls flavors from coffee grounds into the water. Extraction is affected by many factors, including time, water temperature, grind size.

What is Coffee Extraction?

Grind Size and Extraction

Grind size is perhaps the most commonly discussed factor when it comes to coffee extraction. When brewing espresso, the size of the grind and the amount of coffee, or the dose, in the portafilter are the two components which are adjusted on a more regular basis in order to achieve a balanced extraction. Adjusting grind in espresso is also known as “dialling in” espresso.

Coffee Of Various Grind Sizes

Extractions vs. Total Dissolved Solids (TDS)

It is important here to discuss the difference between extraction and TDS. Extraction refers to properties being taken from coffee beans whereas TDS refers to the concentration of these coffee properties in the final brewed coffee. It is possible to have a high extraction but a low TDS in a coffee if too much water is used during brewing. A high ratio of water to coffee would cause the TDS to become diluted in the cup, producing a weak cup, even if lots of coffee compounds and properties were extracted from the bean during extraction. For example, filter coffee is prepared with more water than Americano coffee. Coffee extraction aside, the Americano is a “stronger” cup than filter coffee due to less water and a higher concentration of TDS.

Does Finer Grind Make Stronger Coffee?

Espresso brewing calls for a finer grind compared to other brewing methods such as filter coffee or French press. Espresso coffee is also thought to be stronger than the other methods. This, among other facets, lends to the belief that finer grind means stronger coffee.

Coffee is ground finer in order to increase the surface area of the bean that is in contact with water during extraction. This increased contact causes greater extraction. Therefore, if coffee is ground finer and all other brewing parameters are not adjusted, finer ground coffee will extract more coffee properties to be dissolved into the water, resulting in a beverage with a greater TDS which is therefore stronger. However, if more water is added to the recipe, a coffee that is brewed using finely ground beans would have a lower level of TDS and would be a weaker tasting product.

What Happens if You Grind Coffee Too Fine?

Coffee grind size varies depending on different brew methods for a variety of reasons. If grind size is altered considerably from the recommended specifications of a particular brewing method, it will result in a final cup of coffee that is either under or over-extracted.

It is thought that grinding coffee too fine will result in over-extraction. However, in itself, grinding coffee finer will generally only result in more good properties being extracted from coffee. The main problem with coffee grounds that are too fine is that they pass through coffee filters. Other brewing factors, when increased too much, are more responsible for the over extraction of poor, bitter coffee substances than grind size.

What Is the Best Coffee Grind Size?

As the coffee industry has developed, it has been discovered that specific grind sizes are optimum for specific brewing methods. These sizes are governed by the other brewing and practical elements for each method.

Optimum grind sizes for standard brewing methods are as follows:

  • Cold brew - Coarse
  • Percolator - Coarse
  • French press - Coarse
  • Drip - Medium grind size
  • AeroPress - Fine
  • Espresso - Extra fine
  • Turkish coffee - Powder

Turkish coffee is traditionally ground extremely fine in order to achieve an intense, strong and dark brew. A specific Turkish grinder is usually required as standard industry grinders do not have the capacity to grind finely enough.

Espresso coffee is ground finer than drip coffee because of the added element of pressure during brewing, which speeds up extraction. This will be discussed later.

Aeropress coffee grind size falls in between espresso and drip grind size, as Aeropress brewing can be described as an amalgamation of those two brewing methods. Some pressure is added during brewing but not as much as espresso. The filter is also not as fine as a portafilter. Therefore a fine, but not extra fine grind is used.

Drip coffee brewing is reliant on gravity alone for brewing, therefore a coarser grind is required to allow the water to pass through the coffee within the optimum brewing time.

French press coffee is traditionally ground coarse as the French press filter screen is also coarse.  Finer coffee grounds would pass through the filter and into the coffee cup. The same is true for percolator brewing. However, with good quality equipment, a finer grind size can be successfully employed with French pot brewing.

Cold brew is traditionally brewed using a coarse grind, due to the longer cold brewing extraction time and filtration problems. The idea behind coarse grind for cold brew is that cold brew can get over-extracted due to the longer brewing time. This would result in extractiing unwanted compounds in the final brew. However, in my experience, we are only extracting more of the same compounds, and by diluting your final cup a little more, you can get a great cup. 

Science of Coffee: Tasting Extraction

When Should You Adjust the Coffee Grind?

Coffee grind should generally be adjusted to correct brew time. If coffee is too coarse, brew time will be too short and the grind should be made a little finer. On the other hand, if coffee is too fine, brew time will be too long and coffee will need to be made coarser. Brew time will be discussed in more detail later in the article.

Coffee to Water Ratio

Another main factor that contributes to coffee extraction is the ratio of ground coffee to water. If the ratio of water to coffee is incorrect, the final brew will be unbalanced.

Black Porous Ceramic Paperless Coffee Filter On Glass Jug. Gooseneck Kettle. Electronic Scale. Manual Brewing Still Life

What Is the Best Ratio of Coffee to Water?

The barista ratio for brewing is generally 1:16 or 1:17 i.e. for every gram of coffee, add 16 or 17 grams of water. This translates roughly 16 grams of coffee in an 8 oz cup of coffee.

Espresso is brewed to be much more concentrated with a ratio or 7 grams of coffee to 1 oz of water. Espresso is then often diluted by water or milk.

How Much Water to Add to Coffee at Home

A good general rule of thumb for home brewing, known as the “Golden Ratio”, suggests 1 to 2 spoons of coffee for every 6 ounces of water. This can be adjusted based on taste preference.

Extraction and Coffee Brewing Temperature

Brewing temperature is perhaps the most important factor for coffee extraction. Incorrect temperature, more than any other factor, is usually responsible for over-extraction. The other brewing elements also play a role in over extraction, but normally in conjunction with incorrect temperature, not as stand alone entities.

Standard optimum coffee brewing temperature is between 195 and 205 degrees Fahrenheit and varies slightly from brewing method to brewing method. If coffee is brewed with water that has been directly boiled in a kettle, the coffee will be burnt and over extracted.

Barista Making Drip Coffee In Coffee Shop, using a thermometer

Ideal Brewing Temperatures

Higher temperature increases the rate of extraction. Why not increase the brew temperature to the max, then? Because at higher temperatures, we extract compounds that are undesirable for most coffee lovers. Coffee becomes too bitter if we boil it; it’s over-extracted. If we lower the brewing temperature enough, we cannot extract the bitter flavors anymore, or they are in very small quantities.

For this reason, brewing practices like espresso that already have a high rate of extraction due to other factors, such as pressure, require a lower brewing temperature for optimum extraction. The best temperature for brewing espresso is between 190 and 195 degrees F. With espresso, it is not usually necessary to monitor temperature as the machine is programmed to remain at the correct temperature. This is unless the machine is faulty.

Aeropress brewing temperature varies a lot depending on the recipe. We can afford to lower the brewing temperature below any of the other brewing methods. AeroPress is a combination brewing method. It's a hybrid between immersion and pressure extraction. We also need to extend the steeping time with a lower temperature.

French press coffee is brewed slightly hotter again, at roughly 195 degrees F. Water is cooled rapidly during French press brewing due to its exposure with the air, therefore water at a higher initial temperature yields the best brewing results. The typical glass French press has poor insulation and will lose it’s initial temperature very fast.Remember, a little kick in your brew is not bad. It’s only when you extract too much of the bitter compounds, that we have a problem. That becomes an over-extracted coffee.

Pour-over coffee is brewed a few degrees hotter than French press. This is due to the presence of a finer filter, which slows down extraction. Pour-over brewing water is also in constant contact with the open air and cools rapidly. Pour-over brewing should be done at 200 degrees F. One other factor is that most of the time, pour-over recipes require lighter roasts. Light roasts need hotter water to dissolve the soluble solids in coffee. We’ll show you why in a bit, when we talk about roasting levels.

French press is an immersion brewing method, and all of the hot water is poured at once over the grinds. In contrast, pour-over is a gravitation method, and water is poured over the coffee bed in small batches. This allows the water to cool down a little faster.

Automatic drip coffee temperature is normally pre-programmed and isn’t an adjustable factor. Coffee maker manufacturers build their machines so that at the height of the brewing cycle, drip coffee temperature normally reaches around 205 degrees. This is the top of the brewing spectrum, which makes drip coffee makers prone to over-extracting coffee.

Turkish coffee is sometimes brewed as hot as boiling point. The Turkish coffee is famous for being a strong and intense beverage with an extremely high TDS and so all brewing factors are high for this brewing method. Over-extraction is avoided, when brewed properly, because coffee is added to the water before it is heated as opposed to other methods, with which coffee is only in contact with the water when the water has reached brewing temperature.

Cold brewed coffee is brewed using cold water, with no added temperature.

Brewing Time

Brew time, (or contact time), is the last main element that is responsible for coffee extraction. Brew time is the amount of time that ground coffee is in contact with the water. If other factors are adjusted so that the brewing time is correct, it is likely that the coffee will be extracted well.

Ideal brewing time for espresso is between 20-30 seconds. This quick brewing time is achieved by pressure that is added during brewing.

Aeropress brewing time is slightly longer, normally between 1 and 2 minutes due to the presence of some slight, manually created pressure.

French press coffee takes roughly 4 minutes to brew. If finer ground coffee is used, brewing time will be shorter.

French Press Extraction Brewing Time

Optimum brewing time for pour-over coffee varies considerably as different pour-over brewing methods use different filters with different thicknesses. Standard pour-over coffee makers with standard commercial filters take roughly 2.5-4 minutes. The Chemex, on the other hand, uses a finer filter and extraction time is normally between 4 and 5 minutes.

Cold brewing time falls between 12 and 24 hours, depending on preference and the roast used.

Turkish coffee extraction traditionally takes between 3 and 4 minutes.

Over-extraction and Under-extraction

As previously mentioned, the main cause of over-extraction is temperature that is too high. All other factors in coffee brewing such as time and grind size will generally encourage the good properties from the coffee beans to be extracted.

How Do You Tell If Coffee is Over-extracted or Under-extracted?

You can tell if coffee is over-extracted or under-extracted mainly by taste. Different flavor profiles are extracted at different stages during brewing. Fats, oils and acids are extracted first, followed by sweetness, followed finally by bitter notes which consist mainly of plant fibers.

Why Is Coffee Under-extracted?

Coffee is under-extracted when one or more of the following occur: grind is too coarse, brewing time is too short, brewing temperature is too cold.

Why Does Coffee Taste Sour?

If coffee tastes sour that is a strong sign that it has been under-extracted.

Why is Coffee Over-extracted?

Coffee is over-extracted due to one or more of the following: grind is too fine, brewing time is too long, temperature is too high.

Why Does Coffee Taste Bitter?

A bitter taste in coffee is due to over-extraction of the bitter fibers from the coffee beans.

How Do You Know If Coffee Is Strong, But Not Over Extracted?

Strong, well-extracted coffee will have lots of intense flavors that feel balanced to taste, without any one flavor being overwhelmingly dominant.

Roast and Extraction

Roast is another important factor to be considered when brewing. As with brew time, roast time also influences the coffee extraction. Darkly roasted coffee that has been roasted for longer will release more coffee properties during extraction. The opposite is true for lightly roasted coffee. Therefore, brewing factors need to be adjusted to the specific roast being used.

Roasted Coffee Beans Various Roast Colors

Which Coffee is Stronger - Light or Dark?

As previously mentioned, if the other brewing factors aren’t adjusted for a darker roast, darker roasted coffee will release more TDS. This will result in a stronger coffee, as long as the same ratio of coffee to water is used.

Here is the interesting part about light vs dark roast: Dark roasted coffee contains less caffeine per gram of ground coffee than light roasts. However, a brewed cup of coffee using a light roast will contain less caffeine than one brewed with dark roasted coffee. It's because darker roasts are more soluble, the celular structure is broken from the additional cooking during roasting. 

With a longer extraction time and higher brewing temperatures, we could get more caffeine from a light roast, but w almost never do that because coffee is not that great anymore.

Let me get this straight though: A stronger coffee doesn’t necessarily mean more caffeine, though. Caffeine will be released faster in the brewing process, and increasing the TDS will not considerably increase the caffeine content. So don't think that if your coffee is holding a spoon straight has huge ammounts of caffeine. Unless you know you used three times the amount prescribed in the recipe. (I miss those days...)

How to Make Dark Roasted Coffee Taste Less Bitter?

In order to make dark roast coffee taste less bitter, decrease all other brewing parameters ie. a slightly coarser grind, shorter brewing time and cool brewing temperature than lightly roasted coffee.

Dark Roast Coffee to Water Brew Ratio

In order to compensate for a darker roast, a slightly lower brew ratio of coffee to water is recommended such as 1:15.

Light Roast Brew Ratio

Light roast brew ratio, on the other hand is around 1:16 or 1:17, depending on the specific bean.

Is it Possible To Use Lightly Roasted Beans with Espresso?

Even though espresso is traditionally brewed using medium to dark roasts, light roasts can of course be brewed as espresso, to great success. Light roasted espresso is becoming more and more popular in the specialty and third wave coffee movement.

Typical Tasting Notes from Lighter and Darker Roasts

Lighter roasts retain more of the specific notes from the coffee beans and the region where they were grown. Lighter roasts will also have a lighter and brighter profile.

Darker roasts, on the other hand, will have bolder and smokier notes, due to the Maillard reaction taking place during the extended roasting time.

Adjust Brewing Parameters for Roast Level

Lighter roasts are more difficult to extract, because the cell structure is not as soft as it is with a dark roast. For this reason, slightly higher brewing temperatures, and sometimes finer grind sizes are needed.

Pressure

Pressure is an interesting thing in coffee brewing. We have brewing under pressure, espresso and Moka pot, and we have brewing under vacuum for cold brew. The higher the pressure, the higher the boiling point. The higher the vacuum, the lower the boiling point.

Exposing a liquid to high pressure, in theory, should slow down the brewing time. Vacuum, on the other hand, will speed up the brewing time.

How then, Pressure Speeds Up Brewing Espresso?

Espresso Pulling Kevin Butz Unsplash

The pressure in espresso brewing is not applied statically, that would just stall the brewing almost completely. The pressure is just used to push the water through the coffee grounds with a high force. This increases the agitation in the brew and speeds up the dissolution of the soluble solids in coffee.

During the espresso extraction, along with the dissolution of soluble solids, we also emulsify the oils in the coffee, and mix in gases from the beans. The result is the crema on top of every successfully pulled espresso shot, and a coffee with a distinct flavor, like no other coffee extraction method.

Pump driven spresso machines push 9 bar pressure, standard pressure at sea level.  Pump driven espresso machines are high pressure coffee makers. High pressure is also the reason that well brewed, fresh espresso has a layer of foam or “crema” on top of the coffee.

A a properly brewed espresso is extracted between 20 and 30 seconds. Shots pulled over 30 seconds are overextracted. The reason is again, we expose grounds to a high temperature for an extended time.

Steam based espresso machines typically generate roughly 3 bars of pressure. From a definition point of view, they are still espresso machines. However, the extraction is different. The low pressure does not emulsify enough oils into the shot, hence we don't have crema.

To a lesser extent, other brewing methods also make use of pressure such as the Aeropress and the percolator or the Moka pot. These methods generate up to 1.5 bars of pressure.

Vacuum

The lower the pressure, the lower the boiling point of water. If we lower the pressure enough, we can boil water at room temperature. That means we can boil a cup of coffee at room temperature.

Cold Brew Coffee Brews Faster In Denver

In Denver, because of the high altitude, water boils at 202 degrees Fahrenheit, compared to 212 degrees in New York. This means that at the same room temperature, coffee will steep faster in Denver than in New York. On the other hand, many hot brew coffee recipes can be adjusted to "straight of the boil" temperature for coffee lovers in Denver. 

Some cold brew coffee makers also exist that create an air vacuum when brewing, such as the Dash and Gourmia Brewdini. The vacuum lowers the boiling point of the water, allowing more coffee extraction to occur which in turn speeds up the cold brewing process considerably.

Cuisinart Vacuum Cold Brew Coffee Maker

No Pressure

Most of the coffee brewing methods do not use pressure rely on gravity or immersion for extraction. These processes extract at a slower rate.

Extraction with Gravity

Brewers that rely on gravity are mainly automatic drippers, pour-over, and cold drip coffee makers. Gravity methods rely on the water movement to generate energy. This energy will help dissolve the solutes in coffee.

Immersion Extraction

Immersion coffee makers do not use external energy to brew coffee. Some times an initial stirring is involved, but mostly to saturate the coffee grounds with water and make them fully immerse. Immersion coffee brewing uses Brownian motion as it source of energy for dissolving coffee solutes.

Brewers that utilize full immersion during brewing are the French press, AeroPress, percolator and immersion cold brew.

Other Brewing Factors

Along with the main brewing factors already discussed such as grind size, brew time, temperature, coffee to water ratio and roast, there are several other factors present in particular types of brewing which also contribute to coffee extraction and TDS in brewed coffee.

Agitation or Turbulence

The action of agitation, also known as turbulence, refers to coffee being continually moved and dispersed in the water.

Agitation helps brewing in two ways. Firstly, it ensures that all the coffee grinds are in contact with the water for the entire brewing time. Secondly, turbulence aids in dissolution, in a similar way that stirring helps to dissolve sugar or salt into water.

Take a look at my article on How To Make Cold Brew Coffee Fast. I show in there how agitation works for speeding up extraction.

Filters

The final factor to consider in some coffee makers is the use of a filter; the most obvious of these being drip, or filter, coffee. The use of a fine filter, made from paper or metal, acts as slight obstruction for the water and dissolved coffee solids to pass through during brewing. This obstruction is remedied by grinding coffee coarser. The finer the filter the coarser the coffee. Other brewing factors are subsequently affected and adjusted accordingly. A fine coffee filter also stops some coffee compounds, especially oils, from entering into the brewed coffee, resulting in a cleaner cup. This is considered an advantage and disadvantage by different coffee drinkers and brewers.

coffee filter

The AeroPress brewing method is the only brewing method that consists of a fine filter, full immersion and pressure, resulting in a beverage that has properties typical of espresso, French press and filter coffee.

The French press and the percolator contain coarse filter screens that somewhat filter coarse coffee grinds but do not filter coffee fines. The French press method produces a brewed coffee that is considered to be the strongest due to the lack of a fine filter and total immersion of the coffee grinds for the whole brewing time.

Espresso is brewed using a portafilter, which is coarser than drip coffee filters and, combined with the pressure from the machine, stops all grinds and fines from entering into the coffee but allows fatty and oily properties through.

Finally, cold brew coffee can be filtered in various ways, such as with a paper filter or French press filter screen, depending on the chosen cold brewing method.