Bad coffee is easy to brew. However, avoiding mistakes can go a long way to breaking your lousy coffee blues.

What is lousy coffee (in my opinion, from my experience)? - Under-extracted or over-extracted, too weak or too strong, inconsistent or not repeatable, and just not enjoyable when consumed. 

Here are the common mistakes I corrected to help brew a far superior cup of French press coffee. You may have heard some of these before, but if you don’t understand why you need to avoid the mistake, you might be doomed to making them. So, I’ll do my best to explain some fundamentals and convince you that the extra effort is worth it. 

Avoid these mistakes:

1. Not preheating the French press and cups.

2. Not warming the milk.

3. Not using a scale or a timer.

4. Using a roast that is too dark.

5. Not allowing enough brewing time for light roasts.

1. Not preheating the French press and cups

Problem: Under-extracted. Tastes bad. Cold coffee.

As in the case of the French press, immersion brewing takes a long time. Brew times are typically around 4 minutes but can go longer (see mistake 5 for an example). 

(Note about Immersion brewing: This is a brewing method where the coffee grounds are completely saturated in water for some time. With the French press, coffee grounds are covered with water for a while, ensuring the grounds are “immersed.” The soluble coffee content is dissolved into the water, resulting in brewed coffee.)

The freshly boiled water poured into the French press carafe will cool over the brew time. 

The brewing water must retain as much heat as possible for the heat to be transferred to the coffee grounds. Therefore, the grounds expand when exposed to heat. This causes the soluble coffee to dissolve and the coffee flavor to develop. This process is known as “extraction.”

Suppose the heat is dissipated due to the temperature differential between the boiled water and the cold carafe. In that case, the coffee grounds will not be exposed to sufficient heat over the brew time. This could result in an under-extracted brew. The resulting coffee may taste sour (like a yucky, overly sharp sour, not a tasty, citrusy sour), but it feels thin and flavorless, and salty.

To correct this mistake, pour some boiled water (or parboiled at least) into the carafe to preheat it before you start your brewing process. This reduces or eliminates the heat lost to the French press carafe. 

2. Not warming the milk

Problem: Cold coffee.

Even if you preheat the French press and the cup, the brew will still lose heat, and adding cold milk may make it too cool to enjoy. If you are looking forward to a hot cup of coffee, then lukewarm won’t do.

So if you are adding milk to your French press brew, warm it up before you add it to your cup.

3. Not using a scale or a timer

Problem: Inconsistency due to inaccuracy and not repeatable if you get it right.

A scale allows you to accurately measure the ground coffee and water used in your brew. Knowing the accurate measures helps you understand the ratio of the brew. This gives you an idea of the “strength” of your brew. Check out our article on ratios to get a better understanding of coffee ratios.

Using a timer helps you accurately time the brew. This ensures you are in the extraction time zone you intended for your brew.

Before brewing, you’re making specific decisions about the brew. So using the scale and timer helps you execute those decisions related to the strength and extraction.

Measuring the weight of the coffee and water and measuring the brew time also helps inform your opinions about that brew. Being informed about those inputs enables you to make adjustments if there is something you want to change about the brew. 

And when you get into the ratio and brew time that you are happy with, using the scale and timer allows you to repeat that brew consistently. 

4. Using a roast that is too dark

Problem: Over-extraction. Tastes bad. Too strong.

Dark and extra dark roast coffees have their place. But dark roasts often hide staling and extend shelf-life in commercial spaces while masking subpar bean flavors. So if you are using off-the-shelf supermarket dark roast beans or retail (and non-specialty) coffee shop beans, consider a different dark roast bean source or a different roast entirely when making French press coffee.

Check out - Coffee Bros Guide To Dark Roast

An interesting take - Why Starbucks Makes Burnt Coffee

Don’t get me wrong, I still buy dark roast from the supermarket. But I use it for brewing espresso. I’ve found a brand that offers reasonable quality that I have been able to dial in (as best as a home brewer can).

But what’s so bad about dark roast French press coffee? Typically, the dark roast aroma is what is appealing about dark roasts. Still, when brewed, those same toasty notes turn to burnt, ashy, bitter notes on the tongue. Those harsh flavors overpower other subtle flavors. Also, at this roast level, the soluble coffee more easily dissolves into the brew, giving the coffee a higher strength. Unfortunately, this also adds to the bitterness of the coffee. 

So, the dark roast French press brew is more often overpoweringly bitter. 

There are brewing techniques to get a good brew out of a dark roast, but that adds complexity to what should be a simple, easy brewing process. Check out our troubleshooting article if you want to give it a try in a French press. 

But my recommended solution is to go with a medium-dark roast or anything lighter than that. The French press does a great job with light to medium roasts.

5. Not allowing enough brewing time for light roasts

Problem: Under-extraction. Tastes bad.

Lighter roasted coffee needs time and heat to open up the grounds to release and extract the bright flavors that make light roasts appealing. But if you don’t allow enough time, the brew will be under-extracted (no flavor), sour and acidic in an unpleasant way. 

I’ve experimented with light roast brewing in my French press. I found that the standard 4 to 5-minute French press brew time is not enough to develop a solid flavor and a fuller brew that does not dissipate after it hits your pallet. 

I currently brew my light roasts at 8 minutes and 30 seconds.

Here are my 2 tips to make this work for you:

1. As soon as I start the count down on my timer, I pour half the freshly boiled water into the carafe and put the kettle back on the boil. I then stir the grounds and water until the timer counts down to 8 minutes then I add the rest of the required water.

2. I wrap the French press in a dishcloth to insulate it to maintain as much heat as possible over the long brew item.

Once you apply a longer brew time for light roasts (and a bit of heat management), you’ll be drinking balanced, bright, citrusy French press coffee. 

That’s it, go forth and brew some coffee.