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Why Is My Coffee Bitter?

Let's get to the bottom of your bitter coffee problem. Starting from the top [clever], here is a quick checklist for removing the bitter from your morning cup.

Stale Coffee Beans
How old is your coffee? Is it pre-ground? As a general rule, whole bean coffee stays at peak freshness for about three weeks after it's roasted. After three weeks, the oils and sugars within the coffee bean escape, causing the flavor of the coffee to taste bitter. If you're using pre-ground coffee, the coffee can take on a bitter flavor 24 hours after it's ground. That's why we always recommend buying freshly roasted whole bean coffee and grinding it right before you brew.

Coffee Too Finely Ground
Grinding coffee too fine is a common cause of bitterness (also known as over extraction). How do you know what grind size is right for you? This often requires a little experimentation. The grind you use depends on how you make coffee. For an espresso maker or an AeroPress where the coffee grounds aren't exposed to water for a long period of time, you'll want to use a finer grind. For a pour-over brewing method where the grounds sit in water, such as a French Press or Chemex, you'll want to use a courser grind. For an automatic coffee maker, you'll want be somewhere in the middle. 

Grounds Steeping Too Long
Using a French Press, don't leave the coffee grounds submerged in water for more than 4 minutes. A classic French Press looks beautiful and might take you back to your adventures in Paris. However, you'll want to serve the coffee immediately after it's done steeping in the French Press to prevent your coffee from meeting a bitter (over extracted) fate.

Water Too Hot
195 to 205 degrees is the sweet spot for brewing coffee. Going old school, that's about 2-3 minutes off of boil. If your water is too hot or over boiled, you'll extract the bitter compounds from the coffee. 

Roast Profile
Coffee preferences and tastes are very subjective. A coffee drinker who enjoys a darker roast will often label a lightly-roasted coffee with a more tea like or fruity tasting profile as bitter or tart. This isn't necessarily a brewing issue or imperfection with the coffee. 

I hope this checklist helps you diagnose the cause of your bitter brew. 
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Beyond controlling for freshness, grind, roast profile, time, and temperature, there's a well-known psychological aspect to perceiving bitter coffee: the color of the cup. Our perception of taste comes not merely from the chemical aspects of what we consume and how those bear on our body's senses of taste and smell, but from our own mental state.

Turns our that white cups provide greater contrast for the dark color of coffee, and thereby predispose us to perceive stronger, and often more bitter, tastes from the coffee we're drinking. By contrast, using clear glass to drink from predisposes us to imagine that we're drinking something lighter and sweeter than we'd otherwise detect. The research on the effects of color on coffee taste is compelling, and I can personally vouch for the effects, not just in myself, but having observed hundreds of people at our tastings over the past few years.

As I have a tremendous sweet tooth, it should come as no surprise that my cup of choice is a clear, 5-ounce juice glass. No bitter mugs for me!
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Let's dig into some possible causes of the sour taste. One common cause is under extracting the coffee during the brewing process. This happens when not enough flavor is taken out of the coffee grounds while you are brewing. The longer coffee brews the more sugars are extracted from the grounds making the coffee taste sweeter. However, go too long and you end of with a bitter taste (over extraction). The second cause of a sour taste is more a matter of taste preference. If you are used to darker roasts, you might associate the fruit notes of a lighter roast as having a sour taste. I've even heard a coffee drinker refer to a fruity Ethiopian roast as tasting like someone poured orange juice in their coffee. If the sour taste is a matter of taste preference, I would recommend either sticking with darker roasts, or slowly working your way from darker roasts to medium and then Colombian/ Brazilian coffees to Ethiopian. It's a great way to ease your palate into the full spectrum of coffee tastes. You don't have dive right into the deep end. If you think under extraction is the cause, here's a quick checklist of what can cause under extraction during the brewing process. 

Causes of Under Extraction by Brewing Method
- Doing a pour over?
Try a more medium grind size. If your grind size is too course, it can cause under extraction. 

- Espresso or an AeroPress? 
Try a more fine grind size. Even a medium grind size can cause under extraction with a fast brewing method. 

- French Press? 
You want a more course grind for a French Press since the grounds are steeping in water for a long time. A more common cause of under extraction is steeping the grounds for too short of a time. You should let the coffee steep for 4 minutes before pushing the plunger down and serving. 

I hope this checklist helps you diagnose the cause of your sour cup. 
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Root out evil! Down with sourness in coffee! Our perception of sour taste in coffee has a number of roots: if coffee is over roasted (i.e. roasted too dark or roasted too fast); if the brew process leads to under extraction; if brewing happens too quickly after roasting (i.e. before it "settles"); if the water used has a pH of less than 7 (use pH neutral, filtered water); or if coffee remains in a heated state post extraction (think heat plates on drip brewers).
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There are three culprits to the burnt coffee taste so highly prized among gas station cafes:
  1. Coffee that's over roasted, or where the roast profile heats up too quickly. While some of us love a great dark roast, too much of a good thing can end up tasting bitter and/or burned in the cup.
  2. Coffee that's stale (i.e. spoiled, or over a week or so past roasting for dark coffees) will also taste bitter and/ or burned in the cup.
  3. Once brewed, the heat plates on most drip brewers are a flavor killer. The idea is to keep coffee warm, but prolonged exposure will literally cook the coffee, producing the ultimate in burned coffee taste.
  4. Avoiding burnt coffee is pretty simple: look for small batch roasting that isn't ultra dark; use fresh beans; and don't leave the pot on the heater all morning!
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Yes, yes, and yes. The "staling effect" in coffee is very well understood, but unfortunately that hasn't yet been recognized in the marketing and sale of most coffee in the United States. For a great overview of the mechanisms and their effects on taste, have a look at thisoverview of coffee staling.

The short answer to how coffee stales is simple: tincture of time, multiplied by exposed surface area (whole bean versus ground), and made worse by exposure to heat, air, water, and sunlight. And the most obvious outcome is immediately perceptible in coffee taste, as bitterness (it's literally rancid).

What's amazing is that despite a massive cultural shift towards every shorter food supply chains, with an emphasis on local production and freshness, people still treat coffee as a durable commodity, as opposed to a perishable one, which it is.

Our rule of thumb is pretty simple: coffee is at peak freshness between two and fourteen days post roast. When you buy coffee, buy whole bean only, and grind just before you brew. Most importantly, when you buy, insist on a "roasted on" date as opposed to an expiration date.
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