Burnt / Burned Coffee Taste – What They’re Doing Wrong

This morning, I got my usual coffee made by my favourite barista, and it tasted disgusting and burnt. This is a rarity, her coffees are usually consistently good. It got me thinking about where this burnt taste comes from. I have heard conflicting reasons, and even the google research was not straight forward. This post attempts to explain why your coffee tastes burnt or like ****.

I am a coffee snob. I like my coffee, and I like it bitter. I don’t add sugar, and I choose a cappuccino over a latte because if made properly, it will taste stronger. Although a lot (or even most) coffee shops don’t know this, a cappuccino should be equal parts espresso and milk (and the rest is filled with foam)... whereas a latte should have twice as much milk as espresso.

The first thing to note is that the taste does not come from burnt beans; it’s all in the making. A dark roast can be bitter with “charcoal” characteristics, but a coffee snob will be able to tell whether it’s a bitter roast or whether the coffee has been badly made. Where coffee using the same roast (ie at the same cafe) tastes different depending on the maker or day, that’s a good indication that it’s not the bean type that you have an aversion to.

Source: 123rf.com

Let’s get technical for a moment. Coffee making is actually more science than art. “Extraction” refers to the percentage (by weight) of the soluble coffee grounds that are dissolved in the water. Another issue is which solubles are dissolved – this depends on solubility of different substances at different temperatures, changes over the course of extraction, and is primarily affected by temperature.

Ideal extraction yield is widely agreed to be 18%–22%. The numbers themselves don’t matter; what matters is that there is a range in which coffee is considered to be well extracted. Coffee that tastes burnt has been over-extracted, as bitter components continue to be extracted after acids and sugars have largely completed extraction (and the process should have stopped).

Water temperature is also crucial as it affects the proportions in which solubles are extracted – you want to extract the desired flavors as much as possible, and the undesirable flavors as little as possible. The recommended brewing temperature of coffee is 93 °C. If the water is too hot, some undesirable, bitter, elements will be extracted, adversely affecting the taste.

Don't try to understand this graph unless you like graphs (I didn't...)- it's here to show how seriously some people take coffee making, and how maths and science comes into it. Source: Coffee Cuppers 

But what does all this mean? What is the barista (or under trained 18 year old making your coffee) doing wrong? 

Let’s apply this to the commercial coffee machine. Firstly we need to understand how it works. It works by forcing almost boiling water through packed coffee grounds.There are different types of machines, but most of the ones you see in cafes in Australia are steam driven. They use steam to force the water through the grounds.

Things that will cause over-extraction (and the yucky burned taste):

- When the steam/water is not forced through the beans fast enough. Depending on the grind type, there is an ideal brew time. Over brew and you over extract. This almost always happens because the tamp (that's the pressing of the ground beans into the holder) is too firm - so the barista has either put too much coffee into the holder, or has put the right amount but has stamped it down way too hard. This then means that the water can't get through the coffee as quickly as it should.  Ideally, a shot needs to be timed and the barista needs to measure how heavy the tamp is compared to how fine the beans are grinding at that moment.

- Another issue is that the group head (the coffee holder goes in here) gets very hot, and if the grinds are left in there too long it will adversely affect temperature.

- Dirty, unmaintained machines can contribute to **** tasting coffee – when the machine isn’t working properly, the barista has little hope of getting the pressure right.

In short, it’s the coffee being over-extracted that results in the burnt taste – not burnt milk as some would suggest. Burnt milk is a whole other story, and will also adversely affect the taste of coffee (but doesn’t cause the burnt bitter taste). Burnt milk tastes sweeter than normal milk, is thinner and less creamy and has the aroma of “burnt milk” (overheat milk in the microwave and you’ll see what I mean if you don't already).

Got through all that science? You can call yourself a real coffee snob now! Congrats..

Of course, coffee making IS also an art... some coffee works of art (latte art): 

More here....