bluesman wrote:It's difficult to pry the lid off without trying to evacuate the jar. The threaded band doesn't hold the lid on - it just stabilizes it against the glass, and the temp drop does the rest. You can remove the band once the jar is frozen, and it'll stay well sealed.

The secret is to fill the jar as full as you can, shaking and tapping to settle the beans and leave as little dead space as possible. I pour the entire bottle into the hopper at once - we use it up in a few days. Each "16 ounce" jar holds less than half a pound of beans - it takes all 12 plus my hopper & my wife's to hold a 5 lb bag.

I'm not sure what you are getting at. I was just stating that the lid when vacuum sealed is tight. I dont mind that I have to pry it off at all, its not too hard. Vacuum sealing a dozen jars only adds a few minutes to the process so why not.

It happens regardless of freezing or not. Its a result of the vacuum seal.

jpender wrote:The followup experiment, which I do remember posting about (I think more than once), was to simulate how I actually use coffee.

I don't remember seeing this before, which is too bad because this is a fantastic follow up to your first experiment. This is exactly the kind of posts I come to HB to see

bluesman wrote:As 80% of the tiny amount of remaining gas inside is nitrogen, and none of us can taste a difference with mechanical evacuation, I don't understand the perceived need to do more. Fanatically filling fully & freezing feels fine

Talking about the percentage of oxygen remaining is meaningless unless you have a numerical model for coffee deterioration.

And there are people who have posted on this forum that they can taste the difference with beans that have been stored long enough.

RyanJE wrote:I'm not sure what you are getting at. I was just stating that the lid when vacuum sealed is tight.

The lid when not mechanically "vacuum sealed" is also tight, because of the pressure gradient created across it by lowering the temperature of the closed container - this is also a vacuum seal. Additional evacuation just puts more force on the top, but it's equally "sealed" either way. I and others in this thread have calculated the pressure gradient across the top of a jar sealed at room temp and then frozen to be between 0.15 and 0.2 bar (P1/P2 = T1/T2). A 4" lid has 12 sq inches of surface area, so the force pushing the lid onto the jar is 30+ pounds (depending on the temperatures of your room and your freezer). If you can get the internal pressure down to 0.2 bar, the 0.8 bar gradient across the top puts about 100 pounds on it. But that force is not being applied to the outermost lip of the top because it's sitting over the glass to which it's sealed. And it's flexible, so lifting the edge enough to break the seal is palpably more difficult with your finger tips but doesn't take 3+ times the force.

Two of the questions being discussed in this thread are whether mechanical evacuation improves stability of the frozen beans and if so, why. The facts supporting my opinion are simple:

• A small Ball jar well filled with beans has little room for air.

• The volume present is only 20% oxygen, so there's not much in there to do any damage.

• The process of oxidation is temperature-dependent. Many food science studies show that there's virtually no oxidation of oil in a food matrix at or below 5 degrees C (e.g. this study in Food Chemistry 94: 37-46, 32006). So there's virtually no potential for oxidation of beans in contact with a very tiny amount of oxygen and maintained at 0 degrees F.

• Dropping the pressure another 10+ inches of mercury may make it even harder to pry off the lid, but the marginal reduction in physical oxygen content with each successive reduction in pressure is progressively lower. Even if you suck it down below 0.2 bar, there will be little or no additional change to help preserve the beans better.

I'm done

jpender wrote:Talking about the percentage of oxygen remaining is meaningless unless you have a numerical model for coffee deterioration.

And there are people who have posted on this forum that they can taste the difference with beans that have been stored long enough.

OK, John - I guess I'm not done....

Why bother evacuating if you don't believe that oxidation is a significant cause of deterioration? Regardless of the kinetics, less oxygen is better if it's a factor. If it's not, why work so hard to remove it?

Many food science studies like the one I cite in my last post show that oxidation is essentially nonexistent in food oils at or below 5 degrees C. So the combination of a tiny amount of oxygen and a temperature at which oxidation is virtually unable to proceed suggests to me that the amount of available oxygen is meaningful. You don't need a vacuum sealing system if it's irrelevant (or if it's already so low that further reduction will have no benefit).

I can taste the difference in beans that have been stored long enough too. But we're talking about tasting a difference between beans that have been stored for the same period of time in the same freezer after being put up at ambient pressure vs under mechanical evacuation.

bluesman wrote:But we're talking about tasting a difference between beans that have been stored for the same period of time in the same freezer after being put up at ambient pressure vs under mechanical evacuation.

Yes, that's what I was talking about too. There are people who claim they can taste the difference after enough time has elapsed.

There's no question that oxygen and temperature are key factors in coffee deterioration. But if you can't quantify the effect then using numbers to make a point has no real meaning.

jpender wrote:And is there any merit to the concern that the beans might deteriorate when going from room temperature to freezer temperature and back multiple times?

I came across a file I'd saved a year ago about an informal experiment someone did to test this idea. I'd totally forgotten about it.

Preserving coffee freshness for use on weekends

His conclusion was that yes, multiple freeze-thaw cycles did make a subtle, but detectable, difference.
I think we'd need to see more trials to be confident in his result but it's suggestive.

His experiment is somewhat different than what we're talking about, where the coffee is outside the freezer for a very short time, too short a time to warm completely.

Thanks dh.

I have not stored beans in the freezer for quite some time as I have been sourcing locally. However last time I did, I forgot a few jars in the back for quite some time (maybe 8 months). While the taste was ok when I did end up brewing them, there was definitely a change in taste. I recall that at the time it was reminiscent of freezer burn, or being a bit stale.

For reference I use 8oz jelly jars for storage.

bluesman wrote:OK, John - I guess I'm not done....

Why bother evacuating if you don't believe that oxidation is a significant cause of deterioration? Regardless of the kinetics, less oxygen is better if it's a factor. If it's not, why work so hard to remove it?

Many food science studies like the one I cite in my last post show that oxidation is essentially nonexistent in food oils at or below 5 degrees C. So the combination of a tiny amount of oxygen and a temperature at which oxidation is virtually unable to proceed suggests to me that the amount of available oxygen is meaningful. You don't need a vacuum sealing system if it's irrelevant (or if it's already so low that further reduction will have no benefit).

I can taste the difference in beans that have been stored long enough too. But we're talking about tasting a difference between beans that have been stored for the same period of time in the same freezer after being put up at ambient pressure vs under mechanical evacuation.

That's a cool paper....makes sense--fun to think about the physical/chemical effects at play here. (I think we all know how freezing food, in general, does a great preservation job-- most issues involve freezing damage from ice crystal formation and "freezer burn"......)