What are the signs of under-extraction and over-extraction in coffee? How to avoid over or under extraction in pour-over coffee

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Understanding Coffee Extraction

A few days ago, I was chatting with friends about extraction. When it comes to extraction, we can't avoid two situations that make many coffee enthusiasts feel frustrated—under-extraction and over-extraction. What's the difference between these two situations? How should we improve them during pour-over brewing?

What is Extraction?

First, let's understand what extraction is!

Coffee extraction is the process where water passes through the coffee bed, carrying out substances from within the coffee. During this process, we need to pay attention to many factors: water temperature, grind size, water amount, stirring, etc. Any of these parameters can affect the extraction of a cup of coffee. We generally categorize coffee extraction into: under-extraction, golden cup extraction, and over-extraction.

Golden Cup Extraction

So-called golden cup extraction means that when your brewed coffee concentration falls between 1.2-1.4 TDS, and simultaneously achieves an extraction rate of 18%-22%, it's considered to be within the ideal extraction range. Below this extraction range is what we call under-extraction, while exceeding it is over-extraction.

Under-Extraction & Over-Extraction

Under-Extraction

Under-extraction means that the water hasn't extracted enough substances—there are still many extractable materials remaining in the coffee grounds. At this point, the coffee tastes sharp and sour, lacks sweetness, has a somewhat salty sensation, and feels thin in body with a short aftertaste.

This is because during extraction, small molecular substances like acid and salt are extracted first, followed by sweetness, and finally bitterness. Because not enough substances were extracted, they couldn't neutralize the acid extracted in the early stages, making the entire cup of coffee feel overly acidic and unbalanced.

Over-Extraction

The soluble substances in coffee account for 30%, but what we need at most is only 20%. Exceeding this 20% is over-extraction. Because too many substances were extracted, this makes the coffee carry obvious burnt bitterness, off-flavors, and astringency.

How to Make Adjustments?

So how should we make adjustments?

Let me take FrontStreet Coffee's Yemen Mocha as an example:

1. Water temperature 89°C, powder-to-water ratio 1:15, BG grinder 6W (Chinese standard 20-mesh sieve pass rate 35%), brewing time 1'43". The entry had some rather sharp acidity, thin body, and a "watery" sensation.

I believe this was under-extraction, so I adjusted the grind to be finer.

2. Water temperature 89°C, powder-to-water ratio 1:15, BG grinder 5B (Chinese standard 20-mesh sieve pass rate 70-75%), brewing time 2'20". The entry had rich dark chocolate and caramel sweetness, but with some rubber and woody flavors.

Although this brew no longer had sharp acidity and brought out caramel sweetness and dark chocolate flavors, it also introduced some undesirable flavors, such as woody and rubber notes, plus a somewhat astringent sensation. It felt like drinking through gauze. Therefore, I believe this was over-extracted, so I adjusted the grind to be slightly coarser.

3. Water temperature 89°C, powder-to-water ratio 1:15, BG grinder 5R (Chinese standard 20-mesh sieve pass rate 60%), brewing time 2'06". The entry had a relatively rounded grape-like acidity, with dark chocolate-like bittersweet notes in the middle, and the caramel aftertaste was quite persistent!

Different grind sizes yield different extraction rates during extraction. Coarser grinding reduces extraction rate, causing under-extraction; while grinding too fine increases extraction rate, easily leading to over-extraction. Of course, water temperature also has an impact—lower water temperature naturally leads to lower extraction rate, while excessively high water temperature increases extraction rate.

If you want to identify the reasons affecting your coffee's flavor, I recommend recording the data for each brew session and changing only one parameter at a time when adjusting!

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473