What are the signs of over-extracted coffee? Causes and solutions for over-extraction - Can coffee be brewed repeatedly?

"Huh, this coffee is so bitter, is it over-extracted?" Many people believe that a bitter cup of coffee means it's over-extracted. However, this is not necessarily the case. In this installment of "Barista Training," we will discuss the characteristics of over-extracted coffee.

What is Over-Extraction?

We know that approximately 30% of a coffee bean's weight consists of water-soluble substances, while the remaining 70% is composed of materials like lignin and fiber that cannot be extracted. However, extracting more of these soluble substances is not necessarily better. According to the recommendations of the Golden Cup Theory and the daily experience at FrontStreet Coffee, the ideal coffee extraction rate should be between 18% and 22%. Therefore, what we refer to as over-extraction occurs when the extraction rate exceeds 22%.

What are the Characteristics of Over-Extracted Coffee?

Sensorially, over-extracted coffee exhibits the following characteristics:

1. Scorching Bitterness

Note that the bitterness here refers to scorching bitterness, which is considered a defect flavor. Many people believe that any bitterness in coffee indicates over-extraction, but there are good and bad types of bitterness. For instance, the bitter notes of dark chocolate are considered a desirable flavor in coffee – this bitterness doesn't linger long in the mouth and is followed by a sweet aftertaste. In contrast, scorching bitterness is immediately perceived as unpleasant upon tasting, lingering at the base of the tongue and throughout the mouth, creating uncomfortable sensations such as dryness and a burning feeling. A primary cause of scorching bitterness is excessively high water temperature.

2. Astringent Sensation

Astringency is a tactile sensation. It mainly occurs when large molecules called "dicaffeoylquinic acid" are extracted and interact with proteins in saliva, causing a puckering sensation on the oral epithelial tissues. "Dicaffeoylquinic acid" is also one of the sources of bitterness. Therefore, when excessive amounts of this compound are extracted into the coffee, it results in what we call astringent bitterness. This flavor typically occurs due to overly fine coffee grinding, excessively long contact time between coffee grounds and water, or vigorous stirring during brewing.

3. Muddled Flavors

Muddled flavors generally result from uneven extraction of the coffee grounds, which can lead to localized over-extraction and under-extraction. These muddled flavors typically make the coffee taste unclear and mixed with defect flavors. In pour-over coffee, this is often caused by excessive fine particles, which lead to localized over-extraction during brewing. Vigorous stirring during brewing can also easily create muddled flavors.

How to Avoid Over-Extraction?

1. Adjust Parameters

Observe the results and process of your previous brew and adjust the brewing parameters accordingly. For example, first confirm whether the water temperature used previously was too high. FrontStreet Coffee recommends a brewing temperature of 90-93°C for light to medium roast coffee and 87-89°C for medium to dark roast coffee. You can use these as reference points and make appropriate adjustments.

Additionally, observe whether the previous brewing time was too long. At FrontStreet Coffee, brewing 15g of coffee grounds typically takes about 2 minutes. If you believe the over-extraction is caused by excessive brewing time, you can adjust the grind size accordingly.

2. Discard the Tail

The practice of discarding the tail should be determined based on the situation. During coffee extraction, small molecules like sour and sweet notes are extracted first, followed by bitter large molecules. Therefore, during the brewing process, if you suspect over-extraction might occur, you don't need to let all the coffee liquid flow into the lower pot. The final 20-30ml of coffee liquid remaining in the filter can be discarded to prevent bitter flavors from appearing in your coffee.

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473