We thought we’d release a post on something which we’ve noticed being a point of mystery for most professional and home baristas. There is a distinct lack of information available about the ‘coffee bloom’, though it is something that most are used to seeing (if they brew filter coffee manually at home). We’ve been utilising ‘the bloom’ as it is known to our brewing advantage for a long while. It’s a beautiful thing to watch, and while the term is banded around regularly in recipe talk all over, it is a process rarely understood in full.

So what is Coffee Bloom?

Coffee bloom is the occurrence of a foaming and bubbling during the brewing process, that can be seen as you add water to ground coffee (or sometimes cannot be seen, as you might learn below). It represents mainly is the release of CO2 and some oils from the inside of ground coffee, as water begins to permeate and displace it.

See below some  pictures and a short video of the bloom within various devices. Most obviously it occurs in devices with a narrow chamber such as an AeroPress, where foam and bubbles of gas must rise and leave a quite narrow space. However, the bloom is highly visible in all open-top brewers too, such as cones like the V60, or Kalita Wave. You are often able to view it in domestic batch brewing machines too, such as a Moccamaster.

 

You might be interested to find out that even the crema you see on top of any espresso is in fact a lasting display of the coffee bloom, but for a high-pressure, sealed-in brew method where gas does not escape. The foaming and bubbling of gases and oils does not manifest itself the same way as it would if coffee was brewing in an open top brewing device, by rising to the top of the bed of coffee. Instead, both the pressure and water carry that same foam out in a compressed format that flows with your liquid until it is sat in the cup, where it remains at the top (until you stir it or mix it with something else you’re adding to your drink).

Why do we talk about it?

The bloom is used in recipes and so it is often communicated in discussions of what to do with a particular filter coffee. It’s part of a gentle brewing style most of the time, looking to prioritise evenness and quality in brewing, rather than prioritising simplicity.

Roasters, baristas and trainers use the bloom to describe how someone ought to initially wet the coffee grounds being used. Often it’ll be an instruction for adding your first amount of brewing water: “add twice the weight of the ground coffee you are using”. This one is the most commonly used guideline, because roasted coffee tends to absorb roughly twice its weight before it begins to ‘flood’ and subsequently leak water from its structure.
Adding up to 2 x the weight of your coffee dose in brewing water quantity at the start of your brewing process can help to reorganise the bed of coffee being used in your device, helping it to sit more evenly in your device and end up more resilient to displacement or damage from aggressive pouring.

This wetting phase (where the bloom starts to occur) involves the brewing water displacing the gas inside the roasted particles – causing the bubbling and foaming we see as the bloom. Following that displacement of gas and reorganisation of the coffee ground in the device, the remaining brewing water can then go forward dissolving actual flavour matter evenly without as many issues as if the bubbling and foaming was not controlled by timing. So, we talk about it to help people use coffee with more chance of gaining tasty, repeatable results.

Generally people only refer to the ‘coffee bloom’ as the first period of brewing, for example: “bloom for 30 seconds with 40g water” or “add the first 40g water over 30 seconds to bloom”. But, when you begin adding the rest of your brewing water, blooming does continue. It just does so in a more predictable fashion that you have hopefully accounted for in your recipe, so that the bubbling does not disturb the flow of water through your coffee. That’s the idea at least, but we do see it misinterpreted a little on occasion, for example where a coffee user will add 40g regardless of the dose used, due to never being told that it’s actually 40g because you’re using 20g, and it’d be roughly double any given dose being used. Try to remember that 2 x your coffee dose or a touch less than that, will suffice for doing most of the ‘blooming’ work. No pun intended.

So, blooming is used in a mainly instructional domain as a concept. But, we’re well aware (and come across it a lot) that a lot of people are ‘blooming’ coffee during brewing without understanding it, and how to properly use and account for it. It can be advantageous whether you understand it or not, which is at least very reassuring. But, with proper understanding you can learn a lot from it too! Read the below if you want to get more specific or technical with it.

 

To stir, or not to stir?

To use the example of espresso, mentioned here. With its crema on top of it: stirring agitates the compressed, tiny microfoam bubbles in your espresso crema and separates them from each other. This leads them to eventually break and dissipate. This is, for tasters, a good thing! Ridding your drink of the foam that draws out with it into the cup allows you a clear path to sipping your actual espresso, without tasting the light taint of the foam.
Most purist espresso drinkers agree that although crema is a lovely visual, and to an extent protects the coffee below from immediate oxidisation, it does prohibit your taste of the liquid below. Tasting with the foam will inevitably add a little texture of course, but by flavour alone espresso is often preferred without crema, particularly in blind tasting tests.

Fortunately for most blooms, the actual foam and gas are readily released into the atmosphere above the coffee being used, and if not they are separated from your brewed coffee by a paper filter in between your cup / serving carafe and your brewing device. So, this texture and visual disturbance of things does not generally pose any concern.
Revisiting the espresso drinkers though – they tend to not use the foam as part of their beverage, but instead treat it as an important visual, and an important part of the culture around quality espresso service. Visual indicators of quality, and an appreciation of quality in service are two things that the bloom can help us with – read on below to find out more!

An important visual indicator

Coffee bloom, foam or crema, depending on how it is presented, can be used as a very important indicator of certain key parts of coffee service, whether at home or in a professional environment.

Freshness

Most importantly to us as roasters of coffee, the bloom of coffee represents (in light to medium roasts of Arabica coffees) a suitable level of freshness in the ground coffee being used.

The gases released by coffee during the coffee bloom would simply already have released themselves into the atmosphere from the ground particles or whole beans, if they had been left a while after roasting. So, during brewing we would not see an active bubbling or foaming process as there would in fact be no gas to release from the coffee ground for use.

Coffee’s oils would have begun to stale too at this point, leaving little to no quality aftertaste relative to the actual potential that had been made available through roasting. Both the gas release and oil staling mean a reduction in quantity and quality of flavour available in the brewed coffee.

For a good experience with seeing the coffee bloom, and overall a very positive and valid experience of what a roasted coffee really tastes like, try to use whole beans from fresh coffee harvests, within a maximum of one month after they are roasted. You’ll get the full visual experience and the full sensory experience from the coffee’s maximum available flavour then, too.

Proper storage of coffee

Linked heavily to the above, we also aim to use the coffee bloom as an indicator of how we have been storing our coffee – primarily to gauge whether it has been successful for keeping it fresh or not.
As you can glean from the above, if a coffee gets a little old after roasting, the bubbling and blooming process will suffer. A lack of fervent bubbling, or a lack of activity during brewing would be your cue that you may have gone a little wrong with your storage.

Common issues are storing coffee for too long, or doing so in the extremes of temperature. Higher temperatures than your average room temperatures will accelerate the rate of ageing of coffee, effectively meaning you see less and less coffee bloom despte your coffee perhaps being well ‘in date’ as per roasters’ guidelines. Cold temperatures (below 0 degrees Celsius namely) are great at slowing the rate of ageing in coffee flavour, conversely to the above.

Fridges and freezers are mistakenly seen to be adequate storage sites for coffee, though they’ll reduce the lifespan of coffee if not properly understood. So, that timespan of usage of ‘use within a month after roasting’ ought to be vastly reduced if coffee is going in a hot environment, or if it will be inside a damaging environment such as a fridge.

Fridges are simply a no go – the temperature is not low enough to slow the release of gases not to slow the natural rate of ageing of coffee particles. Fridges also contain moisture, various odours and of course air, all of which will  affect your coffee’s performance when it is ground and brewed, and are likely to leave it showing accelerated ageing during use. A cool, dry place is highly preferable to a fridge. What’s more, you’ll avoid your coffee absorbing those fridge smells too.

Freezers can be a great aid to coffee storage, but it is extremely difficult to get this right. Coffee must be properly airtight before being stored in a freezer. That means an airtight container must be completely full to the brim, or perhaps more easily you can leave it in its original bag (which typically features a one-way valve for gas release during storage) then vacuum / squeeze air out of it, leaving the coffee as airtight as possible for freezer storage. With this method, you’ll actually retain more flavour and life in the beans, and possibly even lengthen the number of days that you can experience a full, bubbly coffee bloom for. 🙂

Pre-grinding coffee

Grinding coffee more than a few minutes in advance of your brewing process is also a big problem for keeping your coffee bloom on the go. We call that pre-grinding, and it’s a big issue for the coffee bloom, but more importantly it accelerates the ageing and staling of coffee tremendously! As we’ve said, the bloom is essentially a function of gas being released from freshly roasted coffee, and a little release of some other compounds too. Ground coffee has been cut up into tiny pieces, usually by a burr grinder. After just minutes (even 10 minutes from grinding) essentially you have allowed most of the gas to escape from within the coffee beans’ structure.
So, if you’re not careful enough to grind immediately before brewing, you’ll see a loss in the coffee bloom (and more importantly, flavour quality) despite it seeming like ‘just a couple of minutes’ in your own head. Before you’ve actually started to brew the grinds, they’ll quickly release the gas that water normally displaces from them, amaking way for oxygen attacking flavour compounds in the beans. It can be a tough thing to take if you’re used to extremely fresh, lively bubbling from your coffee bloom, and then you see a weak, watery brew slurry below you as you make your morning brew – and it really doesn’t take long for this to show!

Be careful with grinding in advance and always try to use your coffee within a minute or so of grinding. Ideal standards are listed below. The coarser the ground particles are for a method, the longer you have before statistically significant staling has occurred:

Espresso – up to 1 minute and no more to ensure freshness and highest levels of crema (bloom in this case)

Pour-over cone (V60, batch brewers, Kalita Wave drippers, Clever Drippers and similar) – up to 3 minutes and no more to ensure lively coffee bloom and highest potential flavour quality available

French press / cafetiere / cupping – up to 5 minutes and no more to ensure a good bloom

With this guideline here, you can potentially see how we as roasters can actually use the information on pre-grinding to gauge quality in service, and to assess conditions of storage in new cafes or in our own procedures. We certainly can’t vouch for the flavour being comparable in pre-grinding, and it follows for the bloom too. Quite quickly it becomes minuscule to non-existent. Within a day of grinding there ill be little remaining at any particle size.

Brewing water temperature

The coffee bloom (as we know it to occur) is a process that presents itself at speed where temperatures are high. This generally has been found to hold true for brewing water between 92 and 96 degrees Celsius being used. The bubbling and foaming is only obviously visible when it occurs at a reasonable pace, as you might expect. Heat is a catalyst for the coffee bloom and for the brewing process in general. At the high temperatures above, both brewing and blooming occur at a quicker rate.
Matter dissolves into hot water much more quickly than in cold water. It follows suit for the gas and oil release during the coffee bloom. A few degrees Celsius in temperature can be a major difference in seeing the visual of the coffee bloom or not (if you’re using a device that can show you it). Too low in temperature can leave the release of gases and oils being very slow and untimely. If the bloom is not aggressive in nature (rapid bubbling) then you could use this as a cue that your water temperature may have been a little lower than you might have liked. Rest assured though, if the blooming process (mainly seen by us as bubbles being formed) occurs in a lively fashion with a little energy to it, you’ve most likely picked a suitable temperature for brewing – whether it was on purpose or not!

Roast degree

The degree of coffee bloom found during brewing is, to an extent, governed also by the roast degree of your coffee. With extremely lightly roasted coffee, less oil and less gas is trapped within the coffee beans at any given size. That means when they’re ground up or as whole beans. The issue this brings about is when you leave a light roast a little longer than a month after roasting for example. Less oil and less gas were there in the first place, so you were already likely to see less of a notable coffee bloom. When you leave the coffee or age it, this reduces to virtually nothing at all!

So, your helpful visual indicator strikes again. You can literally use the blooming process to gauge how lightly roasted your roasted coffee is (internally of course, since it’s simply evident by colour on the exterior of beans anyway).

The converse is true for darker roasts. There is more oil and gas created through cooking a bean to a dark colour degree generally speaking, as the beans undergo further chemical reactions that alter the bean structure and break down compounds into gas. Additionally, the bringing about of higher oil quantities on the surface of the coffee beans during darker roasts actually acts as a mild coating to gas escaping from roasted beans.

Effectively this is making darker roasts actually seem fresher for longer by visual indications. A win in a superficial sense for anyone roasting to dark colour degrees, looking to prove that their coffee is still ‘fresh’ after a long duration of time from its roast date. Of course, it isn’t fresh it has simply been made to appear it due to the creation of oils and in fact extra gaseous material. So, perceive this however you like. Our guidance even with such a coffee would be to begin using it within a week or so of roasting, so to not lose any of the created flavour that may be pleasant for you to try. You May prefer it left a little longer than 7 days from roasting, but you cannot know that until you’ve tried both!

So, use your coffee bloom as a dictator of coffee freshness and roast degree, and you’ll be able to see patterns forming with the bloom as your coffee ages. Less vigorous blooms are coming from lighter or older roasts, generally, and vice versa.

Grind particle size

Another way to use the bloom to your advantage – in a perhaps more nuanced technical way – is to use it to gauge whether you are grinding suitably for your expected results. This is actually most helpful when using a different grinder, or if you are short on time!

Coarse particle sizes mean your bloom will begin to occur more gradually. Finer particles expose the gases more readily to be displaced by water. So, you might see a more immediate and energetic bloom with fine particles occurring during brewing. Use this as your first indicator of whether your grind choice might be successful or not at extracting the flavour you wish to take from your coffee.

If the bloom isn’t happening quickly and you’re making a pour-over coffee, and you know you’ve already added a good portion of your water, you might wonder whether you have chosen a particle size a little too coarse for the brewing device being used. Likewise, if it looks like the bloom occurs rapidly but you’re not adding water rapidly, you may think to speed up how quickly you add the brewing water, or add less brewing water and dilute the beverage afterwards, to avoid over-brewing your coffee.

Perhaps a little more advanced as a technique, but one that is worth eventually taking into account, particularly as you get used to different equipment, devices and more.

Tips for using the bloom

So, a few different things are covered off above about the bloom, what it tells us and how it is generally spoken of. But, what do you do now with this information? Well, our guide would be the below. Use these principles to ensure you see a good set of indicators of and from your coffee bloom.

1. Use the guideline for blooming of adding at or around 2 x your coffee dose in water. Aim to add it gently without damaging the surface or structure of the coffee sat in your device. Then, it’ll reorganise itself adequately for the remainder of your brew to have a higher chance of even brewing. This produces a generally more balanced, representative flavour from the coffee you’re using, usually more closely matching the marketed flavours and notes.

2. Keep water temperature high to avoid a weak, lifeless bloom and the under-brewed coffee that comes with it. Use water at 92-96 degrees Celsius if you’d like to see an energetic process during brewing, and guarantee that you won’t struggle to actually withdraw the flavour from the inside of the coffee being used. Too low in temperature could mean that you do not displace the gas early on or ‘bloom’ effectively. This will mean the dissolving of flavour from inside your coffee dose will become delayed by the lack of bloom, potentially meaning the water passes through your coffee and into the server / cup before any real quantity of flavour has gone through with it! This could be just like removing a tea bag a little too soon – weak, thin, watery!

3. In espresso, use a pre-infusion or pre-wet program if you have it available. Gently dropping water from your machine into the bed of coffee within your machine’s portafilter will allow the espresso particles to reorganise and brew more evenly, while possibly repairing a little human error from distribution and tamping before brewing. This ‘bloom’ is highly valuable for professionals and home baristas alike – it makes any situation more likely to produce a more favourable brewing process, and potentially a higher quality result.

4. Check out how the bloom differs within the same recipe of coffee at a roasted age of one week versus one month old. See if you’ve been storing your beans suitably, in other words. 🙂

5. Use a dark roast and a light roast and note how the bloom alters with roast degrees. You’ll see how it changes with the cooking process during roasting. Very interesting!

 

Do let us know if you’d like any more info on brewing, as we have a whole host of courses in our Coffee Academy from both our own curriculum and the Speciality Coffee Association. We run Brewing modules regularly and if you like to get technical with things, our Leeds Dock site’s Academy is the place to be!

Ollie

North Star Coffee Roasters