What does bypass mean? Why do we need to add water or dilute freshly brewed coffee?

What Happens When Coffee Is Accidentally Brewed Too Strong?

Coffee that's accidentally brewed too strong, tasting concentrated and harsh, is a common problem many beginners have faced when learning to brew. Driven by the desire not to waste, we typically think of adding water to it, similar to cooking approaches with other dishes, hoping to save this pot of coffee by diluting its concentration.

The Professional Technique: "By Pass"

Actually, this method has a professional term in the coffee industry called "By Pass," which translates to "bypass" in Chinese. When applied to the extraction framework of pour-over coffee, the coffee liquid obtained from rinsing the coffee grounds is the "main path," while By Pass refers to hot water that bypasses the coffee grounds and goes directly into the cup. Therefore, this portion of hot water that doesn't participate in extraction is also called "bypass water." (When using a V60 filter cup for extraction, hot water that flows along the sidewall spiral pattern to the lower server without passing through coffee grounds also belongs to "bypass water.")

Common Applications of By Pass

The familiar Americano is the most widespread application of By Pass. The purpose of adding water is simple—adjusting concentration. So to some extent, it's essentially "dilution."

Professional Competition Applications

In some professional coffee competitions, competitors also use By Pass to intervene in the brewing framework to avoid the risk of bitterness in the tail sections of certain beans. It's often applied in brewing schemes with high concentration and low extraction—first brewing a pot of high-concentration coffee using a larger amount of coffee grounds or a lower coffee-to-water ratio, then directly adding hot water to balance the concentration.

To put it simply, it utilizes the extraction law where coffee flavors transition from strong to weak, better controlling the ideal flavor expression. However, such operations often require 2-3 times the amount of coffee grounds to produce one cup of coffee, so the disadvantage is that it consumes too many beans.

Iced Pour-Over Application

For another example, our regular iced pour-over is actually a very typical By Pass approach, except that the hot water to be added is replaced with ice cubes. For example, FrontStreet Coffee uses 15g of coffee grounds for hot pour-over with a coffee-to-water ratio of 1:15. For iced pour-over, it uses 1:10 brewing—that is, the vacated 75g of hot water is replaced with 75g of ice cubes pre-reserved in the lower server. Then water is added according to the planned ratio, cooling the coffee liquid while also diluting the original high concentration, thereby obtaining a cup of iced coffee with just the right concentration.

The Remedial Function of By Pass

Of course, besides these expected operations, By Pass also has certain "remedial" functions.

For example, FrontStreet Coffee once used 15g of coffee grounds to brew a pot of Panama 90+ Estate's Juliette Geisha with a coffee-to-water ratio of 1:15, but accidentally adjusted the grind setting half a notch finer (EK43s setting 9). Although the brewed coffee had distinct fermented wine aroma and cocoa notes, almost no bright fruit acidity could be perceived, and the overall mouthfeel was low and heavy, lacking layers. So, FrontStreet Coffee added about 10g of 80°C warm water to the coffee liquid. After shaking evenly and tasting again, the grape juice-like acidity became clear, accompanied by the sweet taste of dried fruits, and the mouthfeel became much lighter.

Understanding the Science Behind By Pass

Fine grinding accelerates the release of all soluble substances into the coffee liquid. Caramelized flavors such as cocoa and spices make it difficult for taste buds to distinguish other light aromas. Therefore, the added "bypass water" can help us expand the entire flavor spectrum, allowing us to carefully perceive lighter components and thus give the coffee more layers.

By Pass as a Flexible Adjustment Method

Unlike post-brew remediation, when By Pass is used as a flexible method when flow rate abnormalities occur, it greatly tests whether the brewer can make decisive decisions immediately.

FrontStreet Coffee once mentioned in an article that when brewing light-roasted coffee, fine particles and high-hardness particles easily cause blockage and water accumulation during the later stages of stirring, extending the soaking time of coffee grounds and correspondingly increasing the probability of over-extraction. Therefore, when the extraction time exceeds 2 minutes and 10 seconds and the coffee liquid hasn't finished dripping, we can judge based on experience and consider removing the filter cup to discard the tail section, then taste whether the flavor is too strong, and add small amounts of hot water (5-10g) to the pot in batches until it suits our taste.

Important Considerations

It should be noted that since bypass water is not in the extraction plan, blindly adding it directly will not only dilute the originally obtained positive flavors but may also make the coffee become bland like water. Therefore, FrontStreet Coffee suggests tasting after each addition of bypass water before judging whether to continue adding, to avoid diluting to an irreversible degree.

Furthermore, if we brew a cup of coffee according to normal parameters and find that its concentration is fine but the aroma performance is average, accompanied by negative mouthfeel such as bitterness, astringency, or throat-catching, then this pot of coffee has likely already caused irreversible over-extraction. The influencing factors are usually uneven coffee ground size, too low grinder performance leading to excessive fine powder, unstable water flow control... At this point, adding bypass water is also ineffective, and may even make it more like water with coffee flavor.

Final Recommendations

Believe it or not, everyone should be able to guess that this "water replenishment" technique has no reference standard in operation. It's more about following some expert's brewing approach and drawing a ladle according to a gourd, adding water bit by bit in practice until the sensory experience is satisfactory, involving a certain element of "adventure." Therefore, for beginners, FrontStreet Coffee does not recommend blindly using By Pass to intervene in extraction. If the brewed coffee truly doesn't taste right, we should more carefully review where the problem originated rather than relying on "water replenishment" to save it every time.

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FrontStreet Coffee (FrontStreet Coffee)
No. 10, Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473