Coffee facts · Brewing coffee
Whole beans or pre-ground? The clock starts when the coffee is ground
Short answer: When coffee is ground, a clock starts. Up to three quarters of the gas that protects the aroma is gone within 90 seconds, and then oxygen starts breaking down the flavour. That goes for all ground coffee. The difference is how long it takes before the water arrives: weeks or months for pre-ground, under a minute for beans ground at the brewer. The more you pay for your coffee, the more you have to lose.
You pay extra for what disappears first
You have decided on better coffee. Maybe your supplier offers whole beans, maybe you have started looking at specialty coffee. Then it is worth knowing what you are actually paying for.
The difference between an ordinary batch brew and a specialty coffee is rarely in the caffeine or the colour. It is in the aroma, the sweetness and the acidity: what makes a coffee from Kenya taste of blackcurrant and one from Brazil of chocolate. Those compounds are the most volatile in the whole bean. They are the first to leave the coffee.
Do the maths. A cup of batch brew is about 8–9 grams of coffee. For a coffee at €14 a kilo that is around €0.12 a cup. For a specialty coffee at €37 it is around €0.31. So you pay roughly 20 cents extra per cup for flavour. Put in your own prices. The point is the same: those 20 cents are what evaporates if the coffee is left standing ground.
Buying specialty coffee and letting it go stale is paying for something you do not serve.
90 seconds: the starting gun
Researchers have weighed coffee straight after grinding to see how much gas disappears. Up to 75 per cent of the gas in freshly roasted coffee is gone within 90 seconds.
That does not mean you have to brew within 90 seconds. The gas disappears whoever does the grinding, and some of it you want gone. That is why many roasteries let coffee rest for a few days before it is brewed.
But the gas was also what kept the oxygen out. Once it is gone, oxygen starts breaking down the aroma and the oils. That is what makes coffee stale, and from that moment the clock is running.
Think of a loaf of bread
A whole loaf stays fresh for several days. Slice it and leave the slices on the counter, and they are dry by the afternoon. Same bread, same baker. The difference is when you cut it.
Coffee works the same way. In a whole bean the aroma has a long way out and the oxygen a long way in. In ground coffee there is almost no way at all.
Three routes from green coffee to cup
| Pre-ground | Whole beans, ground at the brewer | Roasted and ground on site | |
|---|---|---|---|
| Roasting | At the roastery | At the roastery | At your place |
| After roasting | The coffee is ground and left to degas, or the vacuum pack will inflate | The beans rest and are packed whole in a valve bag | The beans rest at your place, for as long as you choose |
| Transport and storage | Wholesaler, warehouse, delivery | Delivery | None |
| At your place | An open bag behind the counter, one scoop at a time | Today’s beans in the grinder | Today’s beans in the grinder |
| Time from grinding to brewing | Weeks to months | Under a minute | Under a minute |
| Time from roasting to cup | Unknown, often months | Depends on the supplier | You decide, to the day |
Two things in the left-hand column deserve a second look.
The first is that vacuum-packed ground coffee looks fresh: hard, tight, sealed. But for the pack not to inflate, the coffee must first have released its gas. The protection the bean built in has been lost before the coffee is even packed. The pack protects what is left, not what is already gone.
The second is that the makers of packaged coffee themselves say an opened pack should be used up within a couple of weeks. And that is coffee that was already ground when it was packed.
We will come back to the right-hand column.
See the difference with your own eyes
Pour hot water on freshly ground coffee and it bubbles, rises and forms a dome. It is called the bloom, and it is the gas leaving the coffee. Coffee roasted a week ago and ground just before rises in a clear, even dome. Coffee that is three months old sinks with a few scattered bubbles. Pre-ground coffee from an opened bag lies flat.
Lift the lid of the brewer one morning and look. The bloom is a freshness test that needs no instruments, and it takes ten seconds to show a curious guest.
Would you like to be able to judge the coffee before it is even brewed, by roast date, aroma and the look of the beans, and know what actually makes a coffee specialty coffee? Read how to tell if coffee is fresh.
The aroma and the ritual
One of our customers bought the grinder for a reason that was not in our product description. She wanted the room to smell of coffee every time someone ground, and she wanted to show her guests that the bean and the craft behind it deserve respect.
She has the research on her side.
Smell is the sense with the most direct route to the parts of the brain that govern emotion and memory. That is why a scent can bring back a memory faster than a picture. And coffee aroma seems to be particularly powerful. In a 2018 study, people solved analytical tasks either in a room that smelled of coffee or in a room with no scent. The scent contained no caffeine. Even so, those in the coffee room performed better, and the researchers could show why: they expected to perform better. The scent alone raised their expectations.
The study was about maths problems, not about how coffee tastes. But expectation is a word every restaurateur understands. A guest who smells freshly ground coffee before the cup arrives has already decided it will be good.
And there is something almost ironic here. The aroma released when coffee is ground is the same aroma that leaves the coffee. It disappears whoever does the grinding. The only question is where. For pre-ground coffee it is released in a factory, long before the coffee reaches you. If you grind yourselves, it is released in your room, in front of your guests.
It also turns the grinding into a moment. A sommelier opening the bottle at the table, a chef carving the meat in front of the guest. Thirty seconds at the grinder, with a bag of beans beside it, says the same thing: we take this seriously.
So put the grinder where your guests can see it. Not in a back room.
Batch brew forgives nothing
Espresso is strong and concentrated and hides a fair amount. Batch brew does not. It is dilute, and every mistake tastes through. A mistake is not one bad cup but a whole airpot.
In Sweden, where we are based, filter coffee is also what people drink most. Yet it is where most businesses cut corners: a scoop from a bag, or a tin ground this morning. If you serve specialty coffee, batch brew is where your guests will most often meet it.
Five more things you get from grinding on site
1. The right grind for your brewer and your coffee. Pre-ground is ground for every brewer at once. If you grind yourselves, you set the grind for the brewer, the batch size and the coffee you have right now.
2. The same pot every time. A scoop measures volume, not weight, and different coffees weigh different amounts per scoop. Change coffee or roast degree and the pot gets stronger or weaker, and different people fill the scoop differently. Weighed coffee removes both errors.
3. Freedom to change coffee. Whole beans make it easy to run a seasonal coffee or two coffees side by side. No pre-ground stock that has to be used up first.
4. Bags to sell. Grind a bag for the guest who wants to take the coffee home.
5. Something to talk about. A coffee with a name, an origin and a roast date, ground in front of the guest, is a story. Batch brew from a bag is not.
Easier than the scoop
Science Brewing Grinder is grinder and scale in one, made for batch brew.
Put the filter in the holder. The grinder grinds whole beans straight into the filter and stops when the weight is right. An airpot takes about a minute.
The touch screen shows only what you have decided, for example Pot, Airpot and Large airpot. Or just one button. Whoever is at the grinder does not need to know anything about coffee.
If the beans have been standing too long in the grinder, it first grinds away a small amount, so the first pot is not stale. The burrs are made for filter grinding and give an even grind, and that matters: unevenly ground coffee is bitter and sour at the same time.
637 € excluding VAT for grinder and base platform with scale, touch screen and connectivity. Delivery 2–4 weeks.
Compare it with your coffee bill. If you buy 30 kilos of coffee a month at €25 a kilo, that is €750, every month. The grinder costs less than one of those months. The question is how much of what you buy actually reaches the cup.
If you already have a grinder, the base platform is available on its own for 364 € excluding VAT. Ask us whether your grinder fits before you order.
Next step: roast yourselves
With whole beans and a grinder at the brewer, you control everything that happens after the coffee reaches you. What remains is the time before: when the coffee was roasted, how long it sat in storage and how long it was on the way.
If you roast yourselves, you decide. You buy green coffee, which keeps far better than roasted, and roast when you need to. You let the beans rest for as many days as your coffee does best with, and you know to the day how old every coffee in the grinder is. The whole chain, from green coffee to cup, is yours.
Roasting yourselves does not make the coffee better on its own. It gives you control over the one thing you cannot steer today, and it makes you your own roastery.
Science Brewing Roaster roasts 1.2 kilos per batch in 15 minutes, on single-phase 230 volts with a dedicated 10 A circuit, with no chimney. The profile is chosen by scanning the code on the green coffee. The roasted coffee goes into the same stock the grinder draws from, so roasting and consumption are visible in one place.
How Science Brewing Roaster works · Day to day with the roaster
Want the numbers and the research behind this text? Read the technical deep dive.
Frequently asked questions
Do you have to brew within 90 seconds of grinding?
No. The 90 seconds show how fast the gas leaves ground coffee, and that happens whoever does the grinding. What decides the flavour is how much time passes after that. Minutes are barely noticeable. Hours are noticeable. Weeks you can taste.
Is it worth grinding ourselves if we buy an ordinary batch brew coffee?
It gets better even then. But the difference is biggest when there is more flavour to lose. If you buy specialty coffee it is almost a must, otherwise you pay for aromas that never reach the cup.
Is fresher always better?
Not quite. Freshly roasted coffee contains so much gas that it disturbs brewing, which is why many roasteries let coffee rest for a few days. After that, fresh is what counts, and above all freshly ground.
Should the beans stay in the bag or go into the grinder’s hopper?
Keep them in the bag. A valve bag that is rolled up and pressed out keeps oxygen away far better than an open hopper. Lower oxygen can extend coffee’s shelf life up to twenty times. Only pour in as much as you use during the day. The hopper is for today’s coffee, not the week’s.
How long do whole beans keep in the grinder’s hopper?
There is no exact limit, but the hopper is where whole beans age fastest: plenty of air, room temperature and often light. Fill it for the day. If it is quiet, fill it for the morning and then again. Coffee left overnight is not ruined, but it is no longer the best you have.
How should we store unopened bags?
Cool, dry and dark, not on top of the coffee machine or next to the oven. Use the oldest first. Look at the roast date, not just the best-before date.
Should we order 0.5, 1 or 2 kg bags?
Work backwards from your consumption. An opened bag should be finished within about a week.
| You brew about | Used per day | Bag that lasts at most a week |
|---|---|---|
| One pot a day | approx. 60 g | 0.5 kg |
| One airpot a day | approx. 125 g | 0.5–1 kg |
| Three airpots a day | approx. 375 g | 2 kg |
Larger bags are often cheaper per kilo, so choose the largest one you finish within a week. Order so that a delivery is used up within a few weeks of the roast date. Better often and small than rarely and a lot.
How do we get guests to appreciate a good batch brew?
Let them notice it.
- Say what it is. Name the coffee on a sign by the airpot: origin, roaster, two flavour words.
- Let them smell it. Grind where the guests are.
- Show the bloom to anyone who is curious.
- Brew more often and in smaller batches. An airpot that is twenty minutes old tastes better than one that is two hours old.
- Give the staff one sentence. “This is a Kenyan, it tastes of blackcurrant” goes a long way.
- Sell the beans. A bag on the counter says the coffee is worth taking home.
Where does it most often go wrong, and why?
- The hot plate. Coffee left on a hot plate keeps heating and turns burnt and bitter. The SCA brewer standard requires coffee to stay at 80–85 °C for the first 30 minutes without being reheated. Pour it into an airpot straight away.
- Topping up a half-full airpot. New coffee on top of old becomes old coffee. Empty, rinse and fill.
- Dirty airpots and brewers. Coffee oils stick and turn rancid, and that taste carries into the next batch. Wash daily and deep-clean regularly.
- The water. Batch brew is almost all water. Water that is too hard flattens the flavour and scales up the brewer; too soft gives a thin cup. The SCA guideline is around 150 mg of dissolved solids per litre. Check your local water.
- The wrong grind for the batch. A large batch gives a deeper coffee bed and longer contact time than a small one. The same grind does not always suit both.
- The scoop. Volume instead of weight, different for every coffee and every person.
- Stale coffee. Ground coffee opened too long ago, or beans that have sat in the hopper for days.
- Nobody owns the coffee. Appoint one person responsible for cleaning and refilling.
Most of the above is routine, not knowledge.
How fast is an airpot ground?
With Science Brewing Grinder, 125 grams are ground in about a minute, straight into the filter.
What is the difference from an ordinary grinder?
A grinder without a scale measures time or volume. Then someone still has to weigh. Grinder grinds to the right weight and stops.
Sources
- Smrke, S. et al. (2017). Time-resolved gravimetric method to assess degassing of roasted coffee. Journal of Agricultural and Food Chemistry.
- Wang, X. & Lim, L.-T. (2014). Effect of roasting conditions on carbon dioxide degassing behavior in coffee. Food Research International.
- Madzharov, A., Ye, N., Morrin, M. & Block, L. (2018). The impact of coffee-like scent on expectations and performance. Journal of Environmental Psychology 57, 83–86.
- Specialty Coffee Association: Coffee Freshness Handbook, brewer standard for holding temperature, and water guidelines for brewing.
Who we are
Science Brewing exists to end bad coffee. We sell green coffee and build Science Brewing Roaster and Science Brewing Grinder. We roast our own production on the machine, in Halmstad, Sweden.