any explaining required? You take care of coffee supplies, that should be enough

buckersss wrote:I would have thought they would degas and bags expand. I know I've done this with fresh chesnuts and the bag seems rigid the first day. But let it go a week or so and the bag will balloon. So I'd say you have to leave it for more than 1 day to get a conclusion.

I can think of two primary mechanisms for the beans to 'degas':

Gas (mostly CO2) is trapped in the structure of the bean, and that gas will slowly reach chemical equilibrium with the air surrounding the bean. Depending on the genus of the greens and the roast level, that can take days. Gas that exits the structure of the roasted bean won't leave a vacuum - it will be replaced with the surrounding air. So, no net change in overall volume because no gas is produced - it's just redistributed, 'degas' is technically 'regas'.

Despite just having been subjected to profoundly higher temperatures just minutes earlier, the chemical compounds in the roasted beans will react with each other, and some of those reactions may produce gasses. I'm no expert, so it's just my sense that 'maturation outgassing' is more likely to occur with grandpa than my roasted coffee.

Organic materials, like chestnuts, can host organisms that can produce gasses. The surface of the beans I roasted reached 220C, effectively sterilizing them of any living organism. I set the sous vide temperature high enough to suppress the growth of anything I may have inadvertently deposited on the beans before sealing them up, so I'm discounting the possibility that anything was growing and outgassing while in the bath.

Despite all the above, I am gonna try exactly what you suggested, and leave freshly-roasted beans in a well-sealed bag for at least a week. By "well sealed" I mean heat-sealed. I have approximately zero confidence in the integrity of a re-closable (aka zipper) seal.

Marcelnl wrote:perhaps the vacuumization draws (some of) the CO2 out already, indeed a longer wait seems necessary...
I read the problem statement as lack of time to wait for a fresh roast to degas, why not try grinding a small batch post roast and vacuming that for a bit for use for the next morning without sous vide?

Thanks to the HB elders, I learned in a different thread that the grind-a-day-ahead technique was described over a decade ago. I've tried it myself for up to an hour, and it works as advertised. Even thought about grinding, tamping, and locking in the portafilter the night before, but I'm still too brainwashed about the virtues of 'fresh ground' to make that leap.

Milligan wrote:Would love to see one with some beans put directly in the freezer, one sous vided, and one left to age normally at room temp.

Slow resting! Yay, another experiment! Roast/immediately vacuum seal/freeze/wait... weeks, months?

archipelago wrote:It's not just removal of CO2 that improves the flavor of roasted coffee over a period of rest-it's also oxidation. I don't think the oxidative effect would be equal here. Accelerated aging studies function similarly, however: one sample (a reference or control) is kept, and the experimental sample is placed in an environment that is warmer. The rule of thumb for this is that rate of chemical reactions (including oxidative reactions) doubles for every 10ºc increase in temperature-so, in theory, if you had a coffee at 20º and one at 40º, the one at 40 will "age" 4x faster.

You've hit on the two things I was trying to accomplish:

1) I hate carbonic acid, so that CO2 has gotta go. I could have solved the outgassing problem just by drawing a vacuum on the beans (or the grind if I'm really in a hurry). However, raising the temperature might relax the physical bean structure to allow the CO2 to equilibrate faster. I'm hoping that effect is significant enough to obviate having to vacuum seal the bag, which is more of a hassle than just tossing them into a cheap ziplock bag.

2) From what I've read (meaning, I could internet-easily be wrong) there are further chemical reactions that happen in the beans as they rest over the span of a week, and those are good, taste-enhancing chemical reactions. As you point out, raising the temperature will increase the reaction rate, and I run the risk of overshooting the mark and getting bland, overaged coffee. In addition to the non-linear effect of raising the temperature, many chemical reactions have a threshold temperature (activation energy) before they can really kick in. By rasing the resting temperature, I'm changing the relative proportions of the resting chemistry, so I don't expect the accelerated-aged beans to ever taste the same as room-temperature rested beans. But the difference may not be that bad, and perhaps might even be better.

And who knows, I might 'accidentally' drop a blueberry, or a vanilla bean in one of the bags while it speed-rests...

randytsuch wrote:My question is, how do I explain to my wife why I'm using the sous vide to age my coffee beans?

I don't see any good outcomes.

I only occasionally actually 'cook' food in my sous vide: Bulk-proofing for breadmaking. Speed-thawing frozen sauces. Melting chocolate. Decrystallizing honey. Heating aged, distilled spirits to exact body-temperature just before sipping (results can be amazing).

I'm hoping to eventually turn this into an overnight process. Per the saying "they have to sleep, sometime", it can occur when no one's paying attention.

Cool crazy coffee trick idea. I guess if you have a sous vide you're going to sous vide things.

GDM528 wrote:After 24 hours, both bags felt equally rigid, essentially just as stiff as when the original vacuum was pulled. Interesting... I've been programmed to think the little vents on bags of commercially roasted coffee are there to allow the beans to degas post-roast, so I was prepared for my sealed bags to inflate like balloons. LOL, I fooled myself. Now I'm more inclined to think the air vents are meant to keeps the bags from exploding when they're trucked over mountain passes or carried on an airliner.

Here's one roaster's take on CO2, vacuum packing, and one-way valves (he did away with them for his coffee):

But I've never had a bag explode. I have read of roasters who have and this has kept me wary of doing away with the one-way valves before proper testing. However, we have roasted and packaged hundreds of thousands of kilograms of coffee. Sometimes the valves have been faulty and not allowed gas out. In the UK, these bags usually puff up, but haven't exploded. In Malaysia, we use a vacuum sealer and quite often the one-way valves have not prevented gas entering the bags. The leak is audible. And it is in Malaysia that I've decided to do away with the valves. I also contend that, although CO2 is a by-product of the roasting process, there is no 10L CO2/kg roasted coffee released. Rather, I suggest that sealing the bags without using a vacuum results in trapped oxygen that reacts with carbon compounds within the beans producing CO2 gas. Ie 1kg of roasted coffee may produce 10L of CO2 gas if exposed to oxygen, but this amount of CO2 is not within the beans.

There is a theory that vacuum packing is not really necessary as if 10L of CO2 is produced, a kilogram of coffee packed right after roasting will push out most, if not all, oxygen through the de-gassing valve. This presumes that there is indeed 10L of CO2 hiding within the cells of the coffee. If it is in fact the oxidisation of carbon compounds that produces the majority of the CO2, then one is better of using a vacuum packer to remove as much of the air as possible without damaging the beans. The bags I've packed with a vacuum packer only puff up if the valve is faulty. Bags without valves puff up a little.

Another thing worth pointing out is that the presence of a vacuum doesn't necessarily mean the beans aren't degassing. You probably just needed to wait longer.



According to this graph for a medium roast you'd expect around 1mg/g of CO2 in the first 24 hours. And each gram of coffee beans in a vacuum bag has something around 1ml of air space. So 1mg of CO2 adds around 0.5bar, not enough to loosen, never mind inflate, the bag.

With a dark roast the graph predicts about 5.5L of CO2 per kg of coffee after 20 days, and the beans weren't done yet. That's less than what Illy says (10L) but not really that far off.

Update: Ran an experiment to test if vacuum sealing the bags was absolutely necessary. TLDR; nope.

Sous vided two samples of freshly roasted coffee:
One was vacuum sealed and the other was in a quart-sized Ziploc freezer bag. Both went into a sous vide bath set to 60C/140F for 18 hours. Both bags were aggressive 'floaters', but my sous vide bath is fully insulated such that the air just above the water is pretty close.

A few words about my arguably cavalier use of the term "vacuum": I'm using a Foodsaver system to draw the air out the bag before sealing. The pump in the Foodsaver just needs to pull out enough air to make the thin plastic film deform around the contents and create the customer perception of a 'vacuum'. However, the Foodsaver only pulls to a bit lower than one-half atmospheric pressure. Most people can draw a significantly stronger vacuum with their mouth (using their cheek muscles).

Cupped both samples:
When adding hot water to the grind, the vacuum-sealed sample produced slightly more foam. I was surprised by that, as I was expecting the vacuum would draw out more the trapped CO2. Perhaps it did, and the foam is from other mechanisms? The vacuum-sealed sample was ever-so-slightly more aromatic.

Tasted after 5 minutes: Ziploc sample was slightly milder, and the vacuumed sample was slightly brighter. But the difference was very subtle - took multiple slurps to draw a tenuous conclusion.

After 10 minutes: Ziploc sample was slightly more sour, but still quite enjoyable.

After 20 minutes: Back to a dead heat between the samples, and the lukewarm nature of the coffee was pretty distracting at this point.

So yeah, there was a slight difference, and if I were back-seat driving someone doing all the bag prep and sealing work, I would advise them to vacuum seal the roast. But if I were lazy and cheap, l can get away with Ziploc bags. Big-picture was that the coffee was quite enjoyable just 18 hours post roast.

Disclaimer: This was not a rigorous design of experiment, and I'm subject to all sorts of tester bias effects. My goal is to enjoy my coffee sooner after roasting, and I'm not above resorting to mental trickery to achieve that

Did you use the water displacement method with the ziploc bag? At least for regular sous vide it's pretty much functionally equivalent, well actually better for soft food like burgers.

I did try to remove as much air as practical from the ziploc bag, but it still floats pretty aggressively. There's a significant amount of air between the beans, and the roasted beans themselves are quite buoyant. FWIW I don't think I need to exploit the temperature precision of the sous vide; just need get the roast somewhat above room temperature to speed up the resting chemistry. My sous vide has a permanent spot on my countertop, making it a very convenient and relatively safe heat source.


You got me to check: green beans sink, and dark roasted beans float. What about light roasted beans, do they sink, or float?