Blooming and clogging are two important phenomena that significantly affect brewing efficiency and coffee quality during coffee brewing. Blooming refers to the gas release that occurs with the initial wetting of the coffee bed, while clogging describes blockages that cause the flow to slow down or stop during brewing. In this article, both concepts are examined from a scientific perspective; factors such as the relationship between coffee particles and gas release, the role of grind size and flow rate are discussed in the light of academic research. In addition, the interaction between blooming and clogging and scientific suggestions for optimizing these processes are also discussed.
What is Blooming?
Blooming is the intense gas release and swelling process that occurs when a small amount of water is added to freshly ground coffee at the beginning of brewing. Scientifically, coffee beans store high amounts of carbon dioxide (CO₂) gas during roasting, and after grinding, this gas is trapped in the ground particles for a while. When hot water first comes into contact with the coffee, the water displaces the gas inside the grains and pushes it out; this is observed as bubbles and foam in the coffee bed. In other words, the "blooming" seen during blooming is actually the rapid release of CO₂ trapped inside the coffee grains.
A metaphor can be used to understand the relationship between coffee particles and gas release: fresh coffee beans are porous structures that contain CO₂ gas formed after roasting. In order for water to penetrate the coffee during brewing, the gas inside must first escape. Otherwise, gas will escape through the gaps where water is trying to enter, creating an opposing pressure. This situation has been likened to “trying to get in while people are trying to get out of a narrow corridor.” Indeed, when CO₂ is rapidly escaping, it becomes difficult for water to penetrate the coffee particles; water cannot find the paths it needs to flow through the coffee. Adding a little water during the blooming phase and waiting for most of the gas to escape allows water to move more easily through the coffee. In this way, the coffee grounds are thoroughly wetted and the water can start to dissolve the aromatic compounds more evenly.
The scientific purpose of the blooming process is to replace the gases in the coffee bed with water. In academic literature, blooming is sometimes referred to as “pre-brewing” or “pre-infusion” and during this first stage of brewing, water drives the gases in the coffee out and wets each particle. As a result of this process, the coffee grounds expand slightly, creating a suitable environment for the water to come into contact with all areas during the later stages of brewing. The bubbles that form during blooming are especially intense in freshly roasted coffee, as the freshness increases the amount of CO₂ in the beans. If the coffee is very stale (e.g. months after roasting), no significant gas evolution may be observed during blooming because most of the gases have already evaporated.
Both experimental studies and observations by coffee professionals have yielded varying results regarding the effects of blooming time and water amount on extraction . It is generally accepted that skipping the blooming step in brewing completely results in under-extraction of the coffee and a weak (bland or sour) cup in terms of taste. Blooming, even with a small amount of water, allows water to better penetrate the coffee, preventing sub-extraction . Keeping the blooming time sufficient is also critical; common brewing guides usually recommend a blooming time of ~30 seconds. In fact, Taguchi Mamoru (2004) has stated in the literature that 20–30 seconds is the ideal blooming time. Waiting times of 30–45 seconds are frequently used in pour-over recipes, and this range is generally considered sufficient for gas evolution and water absorption. The amount of water used for blooming is typically around twice the amount of coffee (e.g. ~40 g water for 20 g of coffee). This amount is adjusted to provide enough water to completely wet the bed without allowing excess water to pass into the flow. In this way, the water is absorbed into the coffee during blooming, while removing CO₂. However, some baristas have tried blooming with a higher amount of water (such as 3-4 times the amount of coffee) and have stated that it makes it easier to wet all the grounds. The effects of this on brewing have been scientifically studied: For example, an experimental study examined brewing times and extraction using different bloom water ratios. The results showed that as the amount of bloom water increased, the total brewing time increased (i.e. the water drained more slowly). Interestingly, at an extremely high bloom volume (for example, with 8 times the amount of water as the coffee), the time shortened again. This finding suggests that the relationship between bloom water and brewing dynamics is not linear, and that after a certain point, different mechanisms come into play.
Graph: Effect of water used in the blooming phase on drawdown time in pour-over brewing. When bloom water ratio was increased from 1:1 to 8:1 for 15 grams of coffee, brewing time initially increased gradually, but decreased again at extremely high bloom volume (120 g). This behavior can be explained by the fact that when blooming with excess water, the grounds bed becomes saturated and the remaining water passes through more quickly.
Source: Barista Hustle experiment data Academic studies on the effect of blooming time and amount on coffee extraction quality can yield mixed results. Some studies show that the blooming step increases extraction efficiency.
For example, in a coffee brewing experiment, it was reported that the total dissolved solids content (TDS) was slightly higher in brews using a higher proportion of bloom water. This can be attributed to the fact that blooming allows the water to extract more compounds from the coffee. A review reported by Trade Coffee summarized this as “longer bloom = higher extraction efficiency”, but emphasized that this comes at the cost of increased heat loss during brewing. Indeed, while waiting for blooming, the coffee bed begins to cool, which can slow down the next extraction step. Therefore, blooming for too long can upset the balance of flavors. Indeed, one study indicated that excessively long blooming and brewing times can lead to over-extraction, which can carry unwanted bitter and astringent flavors into the cup. This is especially evident in finely ground coffee, because when water is in contact with the coffee for a long time, more unwanted soluble compounds (such as excessively bitter tannins) can pass into the water.
On the other hand, the effects of not blooming or keeping it very short on the taste profile have also been investigated. In an experimental study conducted by Nasko Panov, the effect of blooming on the amount of dissolved CO₂ (carbonic acid) in the cup was measured. Interestingly, no significant difference was found in the dissolved CO₂ levels measured at the end of brewing between samples that had 30 seconds of blooming and those that had not. According to this result, it is suggested that the blooming step does not have a significant effect in terms of acidity reflected in the coffee. The researcher commented as follows: “Brewing the coffee already removes CO₂, a special blooming step does not do this extra.” However, since this study was not focused on taste and only made chemical measurements, it is necessary not to ignore the indirect effect of blooming on taste. In fact, in the same study, it was noted that blooming may have an effect on the extraction distribution or the movement of the coffee bed, which may also change the taste. Coffee professionals similarly state that the main purpose of blooming is to ensure that the water wets the coffee bed evenly, rather than changing the flavor contribution of CO₂. For example, one expert stated that blooming allows the coffee bed to be used more evenly, which has a positive effect on the final flavor.
As a result, the blooming stage is a critical preparatory step in coffee brewing. From a scientific perspective, proper blooming: (i) removes gas from coffee particles, allowing efficient water infiltration, (ii) prevents sub-extractive flavors by increasing total extraction, (iii) but can upset brew balance if done too long or with too much water. A general recommendation is to wait ~30 seconds for bloom before brewing fresh coffee and use about 2-3 times the amount of water as much as the coffee. This range seems to be optimal in terms of both gas release and temperature balance based on experimentation and taste feedback.
What is Clogging?
Clogging is the situation where the flow of water during the coffee brewing process is partially or completely blocked by the coffee bed or filter. In practice, it manifests itself as the water draining much slower than expected in a pour-over brew or the flow coming to a standstill in an espresso shot. Scientifically, clogging usually occurs when fine coffee particles (fines) block the filter or the pores in the coffee bed. These dust-sized microparticles that form when coffee is ground can be dragged with water during brewing and block the pores of the paper filter or fill the holes of the espresso basket. As a result, the water passages narrow or are completely blocked; the flow rate decreases and brewing control becomes difficult. In short, when clogging occurs, the water flow weakens like the flow of a “clogged sink” and proper extraction becomes difficult.
The most common cause of clogging is that the grind is too fine or contains a high percentage of fines. The finer the grind, the greater the surface area of the coffee particles, which can speed up extraction, but it also reduces the spaces between the particles and makes it harder for water to pass through. In many grinders in particular, the finer the grind, the greater the disproportionate amount of fines that are produced. These fines particles tend to move towards the bottom of the coffee bed during brewing, driven by gravity and water flow. This phenomenon, called “ fines migration”, has been likened in physics to the separation of particle sizes known as the “Brazil nut effect” : smaller particles are filtered through the spaces between the larger particles by the effects of vibration and flow, and settle towards the bottom. This dense layer of dust accumulates at the bottom of a V60 filter or the lowest part of the espresso table, blocking some of the filter pores and preventing water from passing through. When a certain threshold is exceeded, a sufficiently large portion of the filter surface becomes blocked and clogging occurs. From this point on, the flow of water slows down and becomes uncontrolled; instead of being distributed evenly throughout the coffee bed, the water begins to flow through channels where it can most easily find its way. As a result, extraction homogeneity is disrupted.
The effect of grind size on clogging has also been recently demonstrated in scientific studies. In a study conducted on espresso brewing, it was observed that a finer grind unexpectedly led to lower extraction efficiency . This adverse effect was explained by the fact that fine grinding restricted the water flow and some parts of the coffee bed remained “blind” . The study stated that beans at a very fine setting caused partial clogging (clogging) in the espresso basket, reducing water permeability, and that the machine had to reach much higher pressure to provide the desired flow rate. Indeed, in the same experiment, the pressure values measured during brewing increased significantly as the grind became finer (e.g., ~3.8 bar for medium fineness, while it increased to ~9.3 bar for very fine grind). This high pressure shows that the machine has difficulty pushing the water and the coffee bed becomes “clogged and solidified” . This partial clogging that occurs in fine grinding causes the water to not pass through the coffee bed equally, and therefore some parts are under-extracted and some are over-extracted. These findings highlight that the optimum point for grinding in pressurized brews such as espresso is slightly above the very fine level, otherwise too fineness reduces efficiency.
Clogging manifests itself in different ways in different brewing methods :
Pour-Over (Filter Coffee) : In methods such as V60 and Chemex, a paper filter is used and the water is filtered through the coffee bed by gravity. Clogging in these systems mostly occurs at the end of brewing or in areas with dense particles. If the grind is too fine or the coffee used is too powdery, the water flow slows down towards the end of brewing and can reach a stopping point called “ stall ”. The fines collected at the bottom of the paper filter block the pores of the filter and restrict the passage of water. In such a case, the brewing time can last much longer than the normally expected 2-3 minutes, and water can even accumulate in the coffee bed, causing an undesirable “watery” extraction. In addition, when the filter is partially clogged, water tends to flow through the edges of the filter, which is the easiest route; this can lead to the coffee in the middle of the bed not being brewed as much as it should, i.e. channeling . The result is an unbalanced extraction profile: Some of the coffee may be over-dissolved (giving bitter flavors), while some may be under-dissolved because it did not make full contact. Professional brewers have also observed that clogging affects taste, especially with pour-over methods – when the filter starts to clog, water can flow around the edges and bypass the centre, and this “false brewing” can leave sour flavours that are not extracted.
Espresso : Espresso made with finely ground coffee under high pressure is the method where clogging effects are most evident. There are hundreds of small holes in the basket of the portafilter used when preparing espresso; ideally, the water should drain evenly through these holes. However, when the grind is too fine or the dosage/volume ratio is inappropriate, it can become blocked to the point where water does not flow at all (as baristas call it, “shot choke” ). In such cases, the machine’s pump increases the pressure to over 9 bar, but the flow is only a trickle or completely cut off. Technically, this blockage is caused by the lack of space in the coffee bed for water to pass through. Clogging not only slows down the flow, but can also cause channeling during espresso extraction. The water quickly passes through the weakest point by opening a tunnel, and the rest remains compressed and dry. In this case, the coffee that reaches the cup can contain both the sourness of the under-extracted parts and the bitterness of the over-extracted parts. In qualitative coffee studies, it has been shown that the fines ratio disrupts the balance of espresso extraction: Grinds with too much fines “easily clog the flow paths, forcing the water to seek alternative channels” , resulting in an uneven brew. Therefore, in modern espresso recipes, it is important to ensure that every point of the coffee bed is wetted evenly (for example, with pre-infusion ) and not to make the grind too fine. A modeling study by Cameron et al. in 2020 also mathematically demonstrated that a coarser grind (with less fines) in espresso provides higher and more consistent extraction, while an ultra-fine grind disrupts consistency.
French Press : French press is a method in which water is completely mixed with coffee, waited for a certain period of time and then filtered through a metal filter. Here, the water flow is not restricted during brewing in the classical sense (because water and coffee initially come into free contact), but clogging can occur when the plunger is pushed down. The French press metal filter is in the form of a porous mesh and very finely ground coffee can easily fill the pores of this mesh. If the coffee used is finer than necessary or contains a lot of dust, the filter screen becomes clogged with this sediment when it is time to filter and the piston cannot go down. Coffee lovers who have experienced this situation know that the piston suddenly hardens and even the glass chamber can crack as pressure is applied. In fact, one source states that the main reason for the French press piston to get stuck is that “the dust from the coffee grinds clogs the metal filter” . The fine dust layer acts like glue and locks the piston. This not only creates difficulty in use; At the same time, coffee that is not fully filtered means that the brewing time is extended, which poses a risk of over-extraction. In the case of the French press, another dimension of clogging is the sediment passing into the cup . Even if the filter is not clogged enough to be overcome, very fine particles will pass through the filter and seep into the coffee, leaving a muddy texture. This can lead to an unwanted bitter taste and a gritty feeling in the throat. For this reason, a coarse grind is always recommended for the French press; the aim is to obtain particles large enough not to clog the filter and to keep the dust content in the grounds low. Coffee ground quite coarsely (coarse-grained) with a well-adjusted grinder will allow the French press piston to descend easily, and the coffee will pour into the cup with an acceptable level of sediment, although not clear.
When clogging occurs, coffee extraction and flavor profiles are inevitably affected. Clogging can increase the amount of solute in water, usually by prolonging the extraction time; however, this increase is not controlled and can have a negative impact on the flavor profile. For example, if the filter is clogged in the pour-over method, the water will be in contact with the coffee for longer than planned and the extraction percentage in the cup may increase (a stronger, more intense coffee). However, at the same time, the coffee in the areas where the water cannot flow may not be brewed enough, while other areas may be over-brewed. In this case, the resulting flavor profile can be an unbalanced cup with both sharp sour notes (from under-brewed parts) and charred bitter notes (from over-brewed parts). Qualitative analysis shows that the irregular flow is perceived on the palate as “spoiled extraction.” In espresso, the taste effect of clogging is usually low yield and “weak body” – the total amount of solute may remain low because the water cannot pass properly, but the incoming liquid may be disproportionately bitter. However, in practice, when the espresso shot is completely blocked, the problem is understood in terms of volume and density rather than the taste profile (for example, an overly concentrated shot of 10 ml instead of 30 ml). In the case of a blockage in the French press, the coffee becomes bitter as the extraction time is extended and the drinking quality decreases as the amount of sediment increases.
In summary , clogging is undesirable and should be avoided for optimal brewing. While the causes are mostly fine grinding and high fines ratio, brewing technique (mixing, pouring) and filter type also affect the risk of clogging. Minimizing the formation of very fine dust by using a good grinder, choosing the appropriate grind size and not disturbing the bed unnecessarily during brewing (e.g. not shaking the filter, not pouring water from too high) are the basic ways to prevent clogging. These points will be discussed in more detail below.
The Relationship Between Blooming and Clogging
The concepts of blooming and clogging may seem to belong to different stages of the brewing process, but they interact with each other. The effect of blooming on the risk of clogging has been a topic of research in both practical and experimental studies in recent years. In theory, blooming can reduce the likelihood of clogging during a brew, because the gases in the coffee bed are removed in advance, allowing the water to follow a smoother flow path. A sudden release of gas accumulation (for example, the violent foaming that occurs when pouring water without blooming) can upset the coffee bed, causing uneven distribution of fines particles. This can obscure the flow paths and cause local blockages or channels. Since this gas release occurs in a controlled manner in advance with blooming, the water can flow more calmly and steadily during the actual extraction phase of the brew. For this reason, many baristas believe that the blooming step helps prevent filter clogging in pour-over brews.
But the interesting thing is that the way blooming is applied can also have a significant impact on clogging. As mentioned above, blooming with a large volume of water for a long time can extend the brewing time and increase the tendency for clogging. An experiment conducted by the Barista Hustle team examined exactly this interaction: it was observed that the degree of clogging of the filter (measured by the drawdown time) increased as the amount of water used in the bloom phase was increased. When less water was used for blooming, the coffee absorbed the water and swelled, but most of the water was still retained by the coffee, so very few fines reached the filter. When the bloom water increased, this extra water started to drain early from the coffee bed, carrying more fines down with it and partially filling the pores of the filter. As a result, the area through which the water would pass during the main brewing phase was reduced, slowing down the flow (tendency to clogging). This effect was demonstrated in the experiment mentioned, with the continual increase in the percolation times when the bloom water ratio was increased from 1:1 to 4:1. However, in a very extreme case (like 8:1), the total time is slightly shorter because most of the coffee bed has already been washed in the bloom stage and the amount of water remaining is less.
Another factor that affects the relationship between blooming and clogging is the speed and style of pouring . In academic terms, this can be considered as the effect of flow rate and turbulence on the coffee bed. Pouring water from a very high and fast angle in a pour-over brew creates stronger turbulence in the coffee bed and causes particles to be displaced. This can accelerate the fines’ transport towards the filter, thus increasing the risk of clogging. In fact, observations have shown that pouring height can have a dramatic effect on clogging – water poured from a high angle can clog the filter more. Just think, if the water hits the coffee bed quickly, it will lift the small particles up and push them to the edges and paper. In contrast, water poured from a low and slow angle provides a gentler brew; the coffee bed moves less, and the fines remain relatively in place. For this reason, baristas in brewing competitions are often seen pouring the water close to the surface and at a controlled speed. In addition, stirring or shaking during brewing also affects the distribution of fines. For example, while gentle stirring after blooming in a V60 brew will ensure even wetting of the coffee bed, shaking or tapping the filter toward the end of brewing (to drain off any remaining water) can suddenly stir up accumulated fines and momentarily clog the filter. A physics study cited by Gagné has shown that even tapping vibrations in filtered brewing can create a convective flow, driving fines to the bottom. In other words, any physical impact applied to the coffee bed has the potential to change particle distribution and increase the likelihood of clogging.
When discussing the relationship between blooming and clogging, it is also worth mentioning the concept of pre-infusion in espresso brewing. Pre-infusion is the process of wetting the coffee by briefly adding water to it before applying high pressure to it in an espresso machine – essentially the equivalent of blooming for espresso. When pre-infusion is applied, water slowly penetrates the dry, compacted, thin coffee bed, pushing CO₂ gas and air bubbles to the top and causing the coffee to expand slightly. This allows the water to move more smoothly through the coffee when the main pressure extraction begins. Many experts state that pre-infusion reduces channeling in espresso and helps the bed to extract more evenly (which indirectly reduces the risk of clogging, because the water flows through all channels rather than just one). Although direct academic publications on this subject are limited, practical experience and some technical reports suggest that pre-infusion improves flow, especially in dark roasts. In summary, blooming or pre-infusion prepares the water flow paths by providing a lower initial flow rate and lower initial pressure to the brewing system, thus preventing sudden blockages.
The balance between the amount of water used during blooming and the risk of clogging is also reflected in practical recommendations. In light of the experiments conducted, coffee brewers are generally advised to “use no more than 2-3 times the amount of water for blooming”. This is because, as mentioned above, using more water can increase fines transport at an earlier stage of brewing and encourage filter clogging. For example, the Barista Hustle team’s experiment showed that brewing time was significantly extended (the filter remained “dirtier”) when 60 grams (4:1) of bloom was made with 15 grams of coffee. However, blooming with around 30 grams of water (2:1) provided enough water to completely wet the bed and, since most of the water is retained by the coffee, very few particles pass through the filter. Therefore, the optimal bloom water is the amount that is sufficient to wet and release gas but does not strain the filter.
As a result, there is a delicate interplay between the blooming and clogging processes. A balanced bloom can reduce the risk of clogging by preparing the coffee bed, but an overly aggressive bloom can have the opposite effect. Academic and experimental data show that optimal blooming practices (with the appropriate amount of water, duration, and pour technique) make coffee brewing more predictable and minimize clogging. Brewers should adjust their recipes to consider these two factors together: for example, blooming a little longer for a very fresh and fizzy coffee, limiting the bloom water for a very finely ground coffee, or making the pour more gentle.
Scientific Studies and Experiments
The science of coffee brewing has made great progress in recent years, with both chemical analysis and physical modeling. There are also several recent scientific studies on blooming and clogging:
Scientific studies on blooming : Although the number of academic publications directly examining the effects of blooming is relatively small, some theses and experimental studies have shed light on this issue. Nasko Panov's study focused on the chemical effect of blooming, measuring the CO₂ levels in the cup at the end of brewing and finding that the blooming step did not change these levels. This study raised questions about the indirect effects of blooming on taste. Again, in an Asian study (Hung et al., 2022), parameters such as grinding degree, water temperature, blooming time and water-coffee ratio in pour-over brewing were experimentally changed to search for ideal coffee extraction . In this study, different blooming times (20 seconds, 30 seconds, 40 seconds) were compared; it was reported that 20 seconds of blooming achieved the highest extraction efficiency, while a slight decrease was observed at 40 seconds. The extraction rate obtained with 20 sec blooming was 18.3%, while it decreased to 17.9% with 40 sec. These data support the idea that the optimum time remains in the range of ~20-30 sec, indicating that very long blooming can reduce yield. Furthermore, the ideal range of 20-30 sec stated by Taguchi (2004) is in line with this experimental result. Another current approach to blooming is sensory analysis: For example, some tasting panels have scored the differences between coffees brewed with blooming and coffees that were omitted. The general consensus is that blooming produces a more balanced and clean cup, but such experiments are mostly in the form of industrial reports and are not fully reflected in the academic literature.
Scientific studies on clogging : Since clogging is related to the physical dimension of coffee extraction, we see studies on this subject especially in the engineering and physics literature. An article published in Matter magazine in 2020, which made a splash in the coffee world, examined espresso extraction with mathematical modeling and experimentation . This study by Cameron and his team tried to optimize espresso quality by systematically adjusting the grinding particle distribution. One of the results is that, contrary to traditional belief, finer grind is not always better for espresso. It has been found that excessively fine grind reduces total extraction by making some areas of the coffee bed impermeable to water and still leaves soluble matter in the discarded coffee. Modeling shows that even under high pressure, water cannot pass through the clogged areas and is directed to other easy paths (channels), which leads to irregular extraction. As a result of this study, it has been suggested that a slightly coarser setting (and perhaps lowering the dosage) in the espresso grind, which does not produce too much fines , can give more consistent and efficient shots. As a matter of fact, some third wave coffee houses have revised their espresso parameters under the influence of this research and achieved higher extraction percentages.
There have also been scientific attempts to understand clogging in the filter coffee field. An analysis reported by Jonathan Gagné on the Coffee Ad Astra platform attempted to define an objective clogging index by comparing the pore size distribution in paper filters with the coffee particle distribution. This approach can be used to predict how prone a particular filter-paper-grind combination is to clogging. For example, in very fine metal filters (disc filters) or in some reusable filters, if the pores are small and uneven, there is a high probability of overlapping with coffee particles, which means frequent clogging. In contrast, some specially manufactured filter papers (for example, brands that claim high permeability, such as Sibarist) are designed with the goal of less clogging. This kind of engineering approach is valuable for optimizing brewing equipment and grinding parameters together.
There are also academic studies that model water flow in a coffee bed. Giacomini et al. (2020) numerically simulated the flow of water through a porous medium in an espresso coffee bed and applied the principles of multiphase flow to coffee. This study aims to better understand how water moves through coffee, pressure and flow changes in silico (in a computer environment), and phenomena such as blockage and channel formation. The model results show that, just like in a soil or filter sand bed, water flow paths are very sensitive to local permeability changes. Permeability in a coffee bed depends on grind size and particle packing. Such simulations can guide future flow profile optimization of espresso machines or ideal distribution of grinders.
In addition, research from a food science perspective has also compared the results of brewing methods. A 2023 study evaluated different filter coffee methods (V60, AeroPress, French Press, etc.) with both chemical analysis (volatile aroma compounds) and sensory analysis. While this study did not directly focus on blooming or clogging, it did highlight the impact of filter material and brewing style on the outcome. For example, it was found that brews using paper filters (V60, AeroPress) produced coffees that were cleaner and more intense in certain aromas (caramel, floral notes), while methods such as the French Press, which used a metal filter, produced more distinct flavors (fruity, roasted notes). This difference is partly related to the effectiveness of the filtration: the paper filter retains more oils and fine particles, leaving a brighter but lighter-bodied coffee on the palate; while the French Press increases the body as fine particles pass into the cup, but some unwanted bitter components may be detected. Indeed, in the same study, it was stated by the panelists that coffee prepared with a French Press received the lowest score in some quality criteria. This finding indicates that even in the absence of clogging, the presence of fines particles can reduce sensory quality. Therefore, preventing clogging (i.e. keeping fines under control) is a critical goal not only for flow but also for taste.
In summary, scientific studies on blooming and clogging provide valuable insights into the optimization of the coffee brewing process. Both experimental studies (e.g. experiments comparing different brewing parameters) and theoretical modeling (such as fluid dynamics simulations) have deepened our knowledge in this area. The findings confirm some of the traditional practices and question others: for example, while blooming is scientifically proven to be beneficial, data-based guidance on how much water and for how long to use it is emerging. Similarly, while we have always known the importance of coffee grinder selection and grinding settings, this is the first time that its numerical effects (on extraction efficiency or flow pressure) have been quantitatively demonstrated. Issues such as uniform particle size distribution to reduce the risk of clogging and filter design are now under scientific scrutiny. These developments show that the art of coffee brewing is increasingly scientifically based and that engineering principles are also coming into play in the quest for the “perfect cup.”
Conclusion and Recommendations
Blooming and clogging are two important interconnected elements in the coffee brewing process, and their correct management is essential to obtain a quality and consistent cup of coffee. In the light of scientific studies and experiments, the following conclusions and recommendations stand out:
Blooming Time and Water Optimization : The blooming step is critical for proper wetting of the coffee grounds and removal of CO₂ gas. Scientific data suggests that a blooming time of around 20-30 seconds is optimal. During this time, the coffee bed will visibly rise and then start to deflate slightly, indicating that most of the gas has been released. The amount of water for blooming should be kept at around twice the coffee mass. For example, 40-50 grams of hot water for 20 grams of coffee is enough to wet all the particles and not drain the excess water. Going above this level, as research has shown, can unnecessarily extend the brewing time, disrupt the flavor balance and increase the risk of filter clogging. In short, do a bit of blooming for each cup , but not so much that you wait minutes. Do not neglect blooming, especially for fresh and gassy coffees (e.g. 1-2 days after roasting), otherwise the water will be restricted from reaching the coffee and will create a sub-extractive, flat taste. Be careful to maintain the water temperature during blooming (this is why it is useful to preheat your brew vessel), as the temperature drop accelerates with long waiting times.
Grind Settings to Prevent Clogging : Minimizing the risk of clogging largely depends on choosing the right grind size. Scientific studies have clearly shown that grinding too finely can cause flow problems. So determine the grind range that’s right for your brewing method. Medium-fine to medium (usually the size of sea salt is recommended for pour-overs like the V60), and a very coarse (coarse) grind is ideal for a French press. For espresso, experiment to find the finest setting that works for your machine’s pressure profile, but if your shots are constantly clogging, go a notch coarser. Try to get a uniform grind : Cheap or poorly maintained grinders can produce excessive amounts of fines, which can lead to clogging. Use a quality burr (grinder blade) if possible, and replace any that have become dull over time. Grinders that produce less “dust,” even on a fine setting, are better for both flow and taste. If you experience frequent filter blockages while brewing, grind one level coarser and try again – you’ll probably find that the flow is improved but the taste is still balanced.
Brewing Technique to Reduce Clogging : Not only the grind, but also the technique during brewing affects clogging. Be careful about the height and speed of the pour . Instead of pouring the water from a very high and powerful stream on pour-overs like the V60, pour as close to the bed as possible and in a controlled manner. This wets the coffee bed without over-agitating it and prevents fines from accumulating in a single spot in the filter. If your brewing equipment allows it (such as a Chemex or French press with separate filtration), you can ensure that the remaining water passes evenly by gently stirring or shaking at the end of the brew; however, do not allow the bottom of the filter to suddenly fill with sediment while doing this. If you are using a French press, do not rush when lowering the plunger after 4 minutes of brewing – apply slow and controlled pressure. If the plunger is too hard, pull it back up slightly before applying force and try again; sometimes this maneuver will disperse the trapped fines and open the flow. These types of small techniques solve clogging problems in the kitchen and also ensure your safety (to prevent glasses or jugs from exploding due to excessive pressure).
Equipment and Filter Selection : The filter material used also affects the tendency to clogging. Paper filters are usually very small in size and retain a large amount of fines; this can have both desirable (clean cup) and undesirable (clogging) results. If you have frequent clogging problems, you can try the more permeable filter papers available on the market, such as the “fast drip” type. For example, some third-party V60 filters or brands like Sibarist promise faster flow (which can mean fewer clogging). When using a metal filter (such as the metal filter of the AeroPress or the French press), clogging is less of a problem, but over time the metal filter can become covered with coffee oils and its pores can narrow. This slows down the flow in the long run. That’s why filter cleaning is important: Just as paper filters should be thrown away after each use, metal filters should also be degreased regularly. In espresso machines, the holes in the portafilter basket can become clogged with coffee oils and micro particles over time; cleaning and polishing them periodically (such as with cleaners like Puly Caff) will maintain flow performance.
Coffee Degassing : An indirect way to prevent clogging is to use coffee that has been aged for a few days instead of coffee that is too fresh. Coffee that is roasted too fresh will bloom more during brewing because it contains a lot of CO₂ and will move the coffee bed more. Coffees that are 4-7 days old after roasting will still have fresh aromas and will offer more predictable extractions as the gas release has calmed down a bit. This can make blooming easier to manage and can reduce the risk of clogging a bit. Of course, coffee that is too stale is also undesirable, as the aromas of coffee that has completely degassed can be faint. The ideal balance is achieved when the coffee is aged for a few days after roasting.
As a result, in order to improve the coffee brewing experience, it is necessary to master both blooming and clogging. By applying blooming correctly, you can prepare your coffee bed for the best extraction, and by preventing clogging, you can ensure that this extraction continues uninterrupted. In the light of scientific studies, some practices that baristas have long fixed with experience have been proven to be correct: For example, simple but effective rules such as “Coarser grind for French press, bloom for V60, thicken the espresso a little if it is clogged” are supported both practically and scientifically. As technology and research progress, perhaps soon brewing machines will be able to measure the potential for clogging with particle sensors in the ground coffee and warn the user or automatically adjust the ideal bloom time. For now, the best guide we have is both the information we obtain from the scientific literature and our own taste. Using both of these, it seems possible to bring every cup of coffee a little closer to perfection.
D.EMRE KURTULUŞ