- Today, we're gonna talk about resting coffee.
We're gonna talk about the sort of science behind
why we rest coffee and cover best practices
for resting it for espresso brewing and also
for filter brewing.
Now, I think resting coffee very quickly becomes
a point of anxiety in someone's coffee journey.
At the start you understand that fresh is good
and therefore you think fresher is better,
and you go online and you buy coffee from a roaster,
and they ship it to you the day it's roasted.
So you're like, "Okay, great.
This is super fresh, therefore it is super good"
And then you hear, "No, maybe not.
maybe fresher is sort of better,
but it still needs to rest and age a little bit
before you brew it"
And then you're stuck with the question of,
"How long should I rest it for?
What's the right amount?
Am bring this to soon?
Am I missing out on something?
Did I rest it too long?
Have most of the good flavors gone?
What's the right thing to do?"
And I think if we understand what's going on
inside the coffee, if we understand how it affects
the brewing process, then you can make an informed decision,
because a bunch of the factors that affect resting
are kind of down to you, your home, your lifestyle,
and your brewing method.
Let's start at the top.
Let's talk about why we rest coffee.
All of this starts in the roasting process.
When you roast coffee, there's a bunch of
chemistry going on, a bunch of browning reactions,
and almost all of those produce carbon dioxide
as a byproduct.
A surprising amount of carbon dioxide.
You'll often see a study cited that says a kilo of coffee
will produce 10 liters of CO2 during the roasting process.
Now, most of this escapes the coffee bean
during the roasting process.
Now, to say that one kilo of coffee does that,
makes 10 liters, I think is confusing
and actually disingenuous.
It produces a lot of CO2, but how you roast it,
especially the darkness of the roast really, really,
really impacts the amount of CO2 that you produce.
Light roasts produce a lot less CO2 than dark roasts.
The darker you roast, the more of these kind of
browning reactions you have, right up until
the point of combustion,
which I don't recommend reaching,
but it does produce an enormous amount of CO2.
Now, as I said, most of the CO2 does escape the coffee bean
during the roasting process, but quite a lot
is trapped inside.
And over time it will slowly leach out.
It'll just sort of come out of the bean,
but there's a couple of factors that determine this.
As I said, the lighter you roast,
the less CO2 that you're gonna have, but confusingly,
the lighter you roast, the denser the end coffee bean is.
That means the harder it is for the CO2 that is trapped
inside it to get out.
Now, a dark roast will produce a lot more CO2,
but the bean can't keep hold of it because that roasting
process has made it so much more porous.
The beans puff out and become less and less dense
and more and more brittle the darker you roast them.
And so, with a very dark roast,
the bean can't really keep hold of the CO2 inside of it.
And that's kind of it.
This is the thing that I really want you to focus on,
which is what coffee do I have?
Again, the higher grown a coffee would be the more dense
the seed is gonna be, the slower it will de-gas.
Now, why are we worried about it de-gassing
in the first place?
Well, when you finally come to brew coffee,
water hitting the grounds really helps
liberate a lot of the CO2.
When you're making a filter coffee, say a V60,
you'll see that in the bloom.
The fresher the coffee is the bigger the bloom you'll see
as you start to sort of pour water onto the grounds.
Again, this is a pretty good visual.
If you take a dark roast, you'll typically see,
especially a fresh one, a much bigger bloom than you would
see in a lighter roast, even if that light roast is
very, very fresh, 'cause it's just really is a lot less CO2
in lighter roasted coffees.
Now, while filter coffee might be a very good visual
explainer of, kind of blooming and about
the CO2 trapped inside the coffee bean,
it really causes trouble when we come to a much more intense
brewing process like espresso.
There, if you have a lot of CO2 coming out of the coffee,
and again, typically you're using darker or more developed
roast that will have a little bit more CO2 than say,
a filter coffee.
But in that scenario, CO2 coming out of the grounds
as the water is hitting, can be very disruptive
to the brewing process, making it harder and harder
to properly extract the coffee.
Therefore, with both filter coffee and espresso,
what we tend to do is rest the coffee for a period of time
to allow some of the CO2 out, hopefully not let any real
staling reactions take place, and then when we
brew the coffee, it's easier to brew and it's easier
to extract and ultimately, will taste better.
Before we get into specific recommendations around resting
coffees for filter and espresso,
I do just want to touch on one other thing that I think
is really interesting.
You can, in certain situations, shortcut the resting period.
This can be done, actually at the roasting stage
in terms of how you cool the coffee.
This was taught to me, it must be 15 plus years ago
by Tim Wendelboe, who had needed to use a coffee
a few days after roasting in a coffee competition.
And what they'd done is they'd used what's called quenching
to cool the coffee.
Traditionally, in a lot of specialty companies,
coffee will come out of the roaster into a cooling tray
and a fan will drag ambient air through the bed of coffee
to cool it down to room temperature
within two or three minutes.
Once you get into roasting very large batches of coffee,
you can't actually do that.
There's too much thermal mass, and if you don't cool
the coffee fast enough, then it can kind of keep roasting
in the tray, and eventually, potentially catch fire
with darker roasts.
What you tend to see, therefore,
are called quenching systems, where you spray a very fine
mist of water onto the coffee beans.
This mist should hit the coffee beans that are about
200 plus degrees Celsius and instantly evaporate.
And that evaporative cooling really drops the temperature
of the coffee beans very, very, very fast.
The more you quench, the more outgassing of CO2 you have
at the same time.
It seems the coffee as a whole seems to stale faster
when it has been quenched.
This is occasionally useful, if you're a roaster
and you really need to brew a coffee very quickly,
especially for espresso, then yes, you can use
just a spray bottle almost, and spray cool the coffee.
You don't want to add water to the coffee beans.
Everything you spray on wants to evaporate.
If you leave water in the coffee beans,
you will rapidly accelerate staling,
and the coffee will taste bad pretty quickly.
This is occasionally done by unscrupulous people
who know that when you roast a kilo of coffee,
you might only get 850 grams out because of loss of moisture
and other things during the roasting process.
If you add some water back in,
you might end up with 900 grams instead,
and you can sell water for the price of coffee,
but that coffee will not taste good and it will not age
well, but that's maybe not your concern
if you're just trying to make as much money as possible.
I can't give you specific instances of this happening,
but it is a thing that you can do,
should you be an unscrupulous coffee roaster
and business person.
Going all the way back, that's kind of the,
the one sort of cheat to really make a difference
to the speed of outgassing.
But, a couple of other things do make a difference.
The temperature in which you store coffee really matters.
You'll see this when you freeze coffee,
you can still have a coffee that at the end of it
has quite a lot of crema when you brew it,
it still tastes really good.
It's like it's still fresh in many ways.
The warmer the environment that you store your coffee in,
the more rapidly it will de-gas.
That can be useful, but know that you're also accelerating
other staling reactions, oxidization, all of the things
that you don't really want to happen to the coffee.
Generally speaking, the kind of room temperature of around
20 degrees Celsius is about as hot as I would recommend
storing coffee.
Though I understand that in certain parts of the world
and certain situations, you can't store it that cool,
but just know you should not rest the coffee as long,
because it is degassing that much faster.
So you'll have noticed that most bags of coffee that ship
around the world have in them, a little valve.
You won't always see it clearly on the outside
of the packaging, there might be just a few holes here.
What's inside?
Generally, something like this.
It's a very simple, usually plastic valve
that allows gas out, but doesn't allow fresh oxygen in.
Know that if you let a bag of coffee degas,
it does not substantially change the quantity of oxygen
inside the bag.
The CO2 does not displace air left inside the bag.
It will displace both CO2 and air together
at a similar ratio, so it's not a cheap way to somehow
gas-flush your coffee by having the CO2 push out any air
in the bag.
Not true, does not work.
This you'll see on bags of beans though.
It's really truly essential on bags of ground coffee.
If you seal a bag of ground coffee without a valve,
it will burst.
The pressure of the gas coming out of the grounds
is usually enough to rupture the seal on a bag,
and it just makes a bit of a mess.
Occasionally, you'll see a bag where the valve has failed
and you might see a puffy bag that looks a bit weird.
That coffee is totally fine.
It's not bad, it's not suffering from a lack of degassing.
It'll still be degassing at a reasonable rate.
It might seem a touch fresher when you very first open it,
but really, it's not worth not buying,
or it's not worth freaking out about if a valve has failed.
Though, just be aware that if it's a lot of
dark roasted coffee in there, again, that pressure
may rupture the bag.
A lot of people like to use storage jars like this,
that's not a bad thing.
They'll use vacuum chambers like this.
These, I think confuse a lot of people.
If you put very fresh coffee into one of these jars that
lets you pull a vacuum and shows you that you've got
a little vacuum pulled, that coffee will degas,
and that will sort of equalize the pressure,
which means that it looks like the vacuum has failed.
That isn't the case.
It's just the beans gassing.
You'll find that the next time you pull a vacuum,
it may take three or four days before it equalizes,
and after that, it never happens again.
It's not a faulty product, it's just gas
coming out of the beans.
You've pulled a vacuum, you've removed most of the air,
so even though it looks like you've lost your vacuum,
what's happened is you basically filled that space
that was air with CO2.
It doesn't mean fresh oxygen has gotten in,
the system hasn't failed.
It's just been an equalization of pressures.
That was a lot of information.
Let's wrap this up by giving you those specific
recommendations about aging or resting your coffee
based on the way that you're going to brew it.
Let's start with filter coffee.
Filter coffee isn't as big of a concern.
Honestly, brewing coffee the next day after roasting
won't taste as good as it could,
but it won't taste that bad.
Maybe 20 minutes after roasting, not ideal,
but certainly the next day,
it's basically drinkable and enjoyable,
but it will get better after three or four days
of good storage.
With darker roasts, if you do enjoy those,
then I would wait less time.
I'd wait maybe two days, but for light roasts,
medium roasts, four or five days is a good starting point.
But I wouldn't worry too much about trying to rest it
to a point of perfection.
If you're blooming the coffee and you're brewing well,
I don't think you're gonna have a big issue,
and if you want to drink it, you can drink it.
With very light roast, very dense coffees, yes,
you might benefit stretching that out to maybe 10 days.
In some cases, even longer.
The taste of coffee that still has a lot of CO2 in it
can be almost like forgotten sparkling water,
where you have a kind of carbonic acid tang to it.
There's an unpleasant sort of sourness,
it'll be under extracted and it generally will taste
a bit sour overall.
Occasionally, if it's super fresh,
you might taste a little bit of almost smoke,
but that's really pretty rare,
especially with lighter roasts.
Espresso is a much bigger deal.
Espresso is much more frustrating and that CO2 level
in the grounds has a much bigger impact.
With light roasts, I would probably be resting the coffee
around 10 days.
I think that's a good amount of time to make sure
it's good for brewing.
You're certainly not gonna start to generate
negative tastes.
Know that there was never that much CO2 to begin with.
So when you start to pull shots from very light roasts,
your crema might look a little thin.
It was always that way.
Light roasts will never produce a very thick crema.
Once you get into a kind of medium roast,
again, eight to 10 days I think is a very good
starting point, just to let that CO2 degas,
there is just a bit more of it,
even if it is easier for it to leave the bean.
And then with darker roasts,
really, a couple of days is probably fine.
You know what I mean?
If you leave it much longer with dark roasts,
you've got a lot of oil exposed on the surface.
You've got a very porous coffee bean.
You should really be concerned mostly about that coffee
going stale, rather than an issue with the CO2 outgassing
or the coffee resting properly.
So fresher is really better with darker roasts.
Again, a reminder that your ambient storage
makes a difference.
If you are freezing it, if you're putting it
in a cold environment, maybe you store your coffee
in a cellar or a basement, or your just house is
a little bit cooler, then you do need to extend
your resting times.
If you live in a warmer house, a warmer climate,
shorten your resting times accordingly.
Pay attention to the roast,
to the altitude of the coffee,
and I think you should have all the information you need
to rest the coffee and have a really great result
at the end of it.
But more than that, don't let it stop you
enjoying your coffee.
Resting it is just there to make it a little easier to brew.
It isn't gonna transform a coffee from disgusting
to amazing, and you're not gonna miss out
on something incredible if it wasn't there
in the first place.
But now I want to hear from you.
Do my recommendations line up with your experiences?
I know it's hard to say what is a light roast,
what is a medium roast, what is a dark roast,
but are these the kinds of guidelines
that you're working with?
Have you found resting to be stressful and frustrating?
Have you had very different results?
I would love to hear from you down in the comments below.
But for now, I'll say thank you so much for watching
and hope you have a great day.