Let me start by saying that “weak” is a terrible way to describe coffee. There are a number of factors involved and terms like weak can vary from person to person. For instance, weak can mean: less caffeine, a light roast, or watery.
Under-caffeinated, watery coffee can be the worst sensation though. Especially when it’s meant to wake you up in the morning.
However, before I discuss specific reasons for weak coffee, let’s first look at factors that affect coffee quality. This will provide some insight into “weak” concepts like caffeine content, bitter tastes, and roast levels.
Coffee Quality Control Factors
The quality of your coffee can depend on a combination of factors. The first starts with the beans being used and the amount of time that’s passed since the beans were roasted or ground.
Beans are deemed high quality based on the crop and how it’s processed and handled. If the beans become stale, it doesn’t matter how “high-quality” they are, they’ll create a lackluster cup of coffee. As a comparison you could use fresh but lower quality beans and compare them to a stale “superior” bean. The result will be that the lower quality bean will taste better.
The goal when it comes to coffee should be to balance the strength and yield. Coffee is comprised of 98% water and the remaining percentage is the amount of extracted coffee. This is the yield from the brew or the quality of the total dissolved solids. If too little is extracted from the coffee then it will miss essential taste properties and result in a bitter drink.
This is why coffee to water ratios are important for optimal extraction. A coffee ratio like 1:1 (1g coffee to 1g water) results in a strong grass-like taste. In this scenario a lot is being extracted because of the amount of coffee but not enough of the desirables to make it enjoyable. On the other hand if you have too little coffee you will get a weak bitter brew.
Though, there is a common misconception where people consider bitter coffee as being weak. As we noted above, using too little coffee may result in a bitter brew. This can be true to an extent. If you were to brew your coffee and allow the grounds to steep (changes based on grind size), the desirables would still be present in the first third of the brew; As the extraction tapers, the bitter components start to shine through.
Some Reasons for Weak Coffee
1. The Water
We noted above that coffee is 98% water. If your tap water tastes bad then the brewed coffee will taste just as bad or worse. It’s best to use filtered water or a water softener.
The next thing to discuss is the temperature of the water. The Speciality Coffee Association notes that for optimal extraction of the coffee the water needs to be in the range of 195 – 205 degrees fahrenheit. This results in the best flavors being extracted from the coffee. If the water isn’t at the optimal temperature then it will be under-extracted and result in a weak brew.
2. Bean Roast, Grind Size, and Storage
Each brew method has a preferred grind size that extracts the most flavor components from the bean. The most common mistake is using too coarse of a grind. Large grinds have more surface area causing the water to flow too quickly which under-extracts the coffee.
Another issue can stem from the beans being over-roasted. The roaster may have also “baked” the coffee which is a term describing a flat taste. This insipid taste is a result of roasting the beans with too little heat over a long period of time.
As we mentioned above, stale beans are bad beans. Improper storage results in the beans becoming oxygenated. The process of degassing should be prevented as much as possible. This means you should avoid buying too many coffee beans and grinding them as you need them.
It’s important to understand the nuances of coffee and factors that affect the flavor profile before assuming that certain tastes are a result of weak coffee. Proper care of your beans, grind size, storage, and water are all important factors that can affect the coffee before it’s even brewed. As long as these are addressed you won’t experience a “weak” cup of coffee.