Editor’s note: A version of this post originally appeared in Perfect Daily Grind on June 28, 2017
Home preparation is one of the amazing things about coffee that sets it apart from similar specialty food industries like cocoa, beer, or wine. If you drink coffee at home, you are probably doing at least a little work, like grinding the beans or pouring hot water. This kind of preparation work simply isn’t expected of you if you were to unwrap a chocolate bar or pour a glass of Chardonnay.
There’s also a lot more science and technique involved in making coffee than you might expect! Many people struggle to make great coffee at home; recreating a great cafe experience of a cafe can be difficult. So, if you’re brewing and could use a few tips, understanding the lexicon of coffee preparation can dramatically improve your skill-set and results. Let’s take a look at some common terms and concepts.
Read on to answer some basic brewing questions, including: What are the differences between immersion and infusion? What are extraction, solubility, and TDS, and what do they have to do with my coffee? Why are brew ratios and extraction percentages helpful? We’ll also look at some easy ways to make your coffee taste better, like agitation, the “bloom,” and pulse pouring.
Extraction & Solubility
Scientifically speaking, brewing is the process of extracting the soluble material in roasted and ground coffee. When we talk about coffee’s solubility, we’re speaking of the hundreds of unique compounds in the miraculously complex roasted coffee bean that are extracted into the brewed coffee. Liquid coffee typically contains the following water-soluble compounds:
- Caffeine (bitter)
- Acids (sour and/or sweet flavors like oranges, apples, or grapes)
- Lipids and fats (viscosity)
- Sugars (sweetness, viscosity)
- Carbohydrates (viscosity, bitterness).
Solubility and extraction can be affected by a wide range of things, like the genetic characteristics, grind size, water mineral content, roast degree, and brew methods.
Sometimes a brew method that works well for one type of coffee might not for another, so getting the perfect brew can require some detective work. Baristas will often refer to “dialing in” a coffee, typically starting with a single recipe, and then making adjustments in dose or grind setting to affect the flavor until they get an extraction with which they’re happy.
Let’s dive deeper into brewing by dividing it into two basic categories: Immersion and Infusion.
Brewing by immersion means that the coffee grounds are fully submersed in water, which extracts the coffee over time.
Probably the most common immersion brewing method is the French Press, but others exist, including Vacpot Siphons, the Clever, the AeroPress, and the coffee industry’s standard quality evaluation technique called Cupping. Most cold-brew methods that involve a long soak (like a Toddy) are also immersion-brewed.
Immersion can be a fairly hands-off method of brewing. Just add water and wait; 4 or 5 minutes is pretty standard for hot coffee.
Nearly all immersion brews will also need filtration. French Presses use a metal filter, the Clever uses a paper one, for example, but both serve to remove coffee grounds and the finest particles from the final brew (paper filters also remove some of the oils and lipids from the coffee).
Extraction slows down as immersion brew time extends. This is because as coffee solids dissolve into the water, the brew becomes gradually more and more saturated. The water “fills up” with coffee solubles and is less and less able to hold more of them.
This doesn’t mean you can’t get a great cup of coffee, or a strong one for that matter, from immersion brewing. But it could mean that you may need employ a few tricks to get the optimally extracted brew. We’ll look at some of these a little later in the article.
Infusion brewing involves water constantly flowing through a bed of ground coffee and a filter. Basically all drip brewing methods work by using infusion: the Chemex, the Kalita Wave, and the Hario V60 are common manual drip methods, but even an auto-drip machine like a basic Mr. Coffee, a high-end BonaVita, or a batch brewing Fetco are all infusion brewers.
Infusion is a little more efficient at extracting coffee solubles than immersion. It solves immersion’s saturation problem with a constant supply of fresh water. This means that more soluble material is able to be extracted into the beverage, provided enough hot water is added… up to a point, of course. Eventually the hot water will have extracted all of the coffees soluble material.
Brewing using infusion can also present some challenges. Manual methods are susceptible to bad pouring techniques. For example, infusion methods run the risk of channelling, where a stream of water finds an easy route around the ground coffee and doesn’t extract. Additionally, if coffee is ground too finely it can prevent the passage of water entirely, resulting in abnormally long brew time or filter baskets that overflow, ruining your coffee and dirtying your countertop.
Technically, espresso is a form of infusion, but there are many differences that put espresso into its own category. The most important difference is this: espresso is a coffee extracted under pressure. Any coffee can be extracted as espresso under the right conditions using the proper equipment.
Espresso also differs because the serving size is typically much smaller, usually just 20-40 mL. It is also much more concentrated than regular drip coffee. A finer grind and pressurized water enable quicker and more efficient brews, usually in just 20-30 seconds.
Finally, espresso is also different because the brew ratio differs from standard drip or infusion methods. Let’s take a look at the importance of this relationship between quantity of water and coffee.
A coffee’s Brew Ratio is the comparison between the dose of ground coffee and the amount of water used to brew. Brew ratios are convenient for scaling up or down the amount of coffee you brew.
If you were to ask a barista what their standard brew ratio for a drip coffee might be, they might say one-to-sixteen (1:16) or sixteen-to-one (16:1). That means for every gram of ground coffee, they’re adding 16 grams of water. Most coffee preparations are made between 1:15 and 1:18. However, because espresso is so quickly and efficiently extracted, typical ratios are closer to 1:2.
All this talk about ratio necessitates a moment to relate the importance of measuring accurately. Measuring both your coffee and your brew water is crucial to pouring these ratios correctly. It will also help you to easily repeat a recipe. A digital gram scale, especially one that is waterproof and has a protective covering from heat, will become your most trusted tool when crafting coffee at home. Weight, not volume, is the best way to quantify your brew recipes.
Refractometers & TDS
Additionally, you can quantify extraction using a refractometer. This tool works by measuring how much a substance (such as dissolved coffee compounds) changes the direction of light beams in a solution. It then infers the amount of Total Dissolved Solids (TDS) in a solution based on the interference to a light beam’s normal path. The more solids, the more the direction of the light changes.
When people talk about a coffee’s strength, it’s the TDS to which they’re referring – whether or not they know it. More TDS equals “stronger” coffee. Strong coffee has a higher ratio of solubles to water, but that doesn’t necessarily mean better coffee or good extraction.
Using TDS measurement in combination with Brew Ratio, you can determine Extraction Percentage. This tells us how efficiently the dry ground coffee was dissolved into the water that we drink as coffee. Used together, these two measurements are a powerful tool for dialing a coffee into its best tasting brew.
I mentioned earlier that it is possible to affect the way a coffee brews using a few techniques that could potentially improve flavor. Let’s look at a few of these.
Agitation is stirring or otherwise disturbing the bed of coffee grounds. Doing so during immersion or infusion brewing will usually increase your extraction.
It’s especially useful for immersion brew methods, for two reasons. First, it breaks up the crust of wet coffee grounds that float to the surface. Ever tried to push the plunger down on a French Press without stirring first? It’s not easy without stirring!
Second, because immersion brews can become saturated before the coffee is optimally extracted, stirring can help abate under-extracted brews.
Bypassing is adding water to brewed coffee. It’s a simple way to dilute your cup. If you like the flavor of strong coffee, but dislike the overly viscous mouthfeel, just add a little water. You’ll reduce the brew strength without affecting your brew ratio or extraction percentage.
You can get pretty technical with this if you like, weighing your bypass water and comparing pre and post-bypass TDS to achieve optimal results.
Pulsing is a term used to describe adding a little water at a time to an infusion brew. Rather than a constant stream, pulsing allows the coffee grounds in the filter bed to settle before adding more water.
This technique can be used to compensate for fresh coffee. Done consistently, pulsing will help improve consistency and efficiency of extraction.
Sometimes called “the bloom,” preinfusing is technique that introduces just enough water to saturate the grounds. Used as a precursor to infusion, baristas usually use about a 30-60 second wait time before continuing with the rest of the brew.
Much like pulsing, preinfusion can help consistently brew fresh coffee, and will improve the overall quality of the extraction for most drip brew techniques.
Practice & Perfection
Even though all the technical language associated with brewing coffee can be intimidating, in practice it’s not so tough. Repetition and attention to detail will always be your friends if you want to make consistently great coffee, whether behind the bar or at home. Practice, albeit cliche, will get you pretty near close to perfect.