Hi,

I brought back 29 bags of beans from roasters in Sydney, Canberra, and Melbourne, and want to freeze the beans after vacuum packing them. Is there a reason to open the bags (besides wanting to weigh doses or whatever), or can I just vacuum pack the whole bags? I am thinking of doing the latter as a first step as it'll be faster, and I can always re-portion later when I open bags.

The bags are all simple bags with a CO2 valve. A couple of them look vacuum packed from the plane ride, though they were not packaged as such. They simply seem to have had all the air forced out of them during the flight for some reason.

I am not aware of any reason to open the bags, assuming they are packed in a standard bag with a one way valve, so long as any excess air is out of the bag which it should be. Interested in what others think though.

When you freeze the beans the trick is to not let them thaw before you grind them. So however you pack the beans, in their original bag (which is fine) or vacuum sealed, just be mindful that it is best to weigh individual portions (18 grams or whatever weight you will be grinding) and grind them before they defrost.

The reason is that beans that are thawed lose a lot of viscosity / body as well as flavor. Some people do t mind this diminished viscosity and flavor but for me it is the equivalent of using beans that are well passed their "best by" date.

BTW very clever resource here http://www.ielogical.com/coffee/FrzCalc/FrzCalc.php thanks to @cafeIKE

The "CO2 valve" is a one-way valve and the reduced cabin pressure (or that in the cargo hold) effectively "vacuum packed" them during the flight. The ones that don't look vacuum packed suggest that their valves are not quite as well-sealing as the others.

Vacuum packing in the original bag, assuming it has a one-way valve works well. Without a vacuum packer (or short on time), squeezing out as much air/gas as possible, taping over the valve and tossing in the freezer is functional.

There's a lot of mythology around freezing coffee and very little in the way of reasonably controlled studies. Grinding while frozen works, and I have not seen anything to suggest that it damages the burrs. Grinding while frozen does noticeably change the grind setting. There are a variety of opinions around the effectiveness of freezer compartments, upright freezers, frost-free freezers, chest freezers, ... There are also a variety of opinions around freezing an entire bag and then allowing it to come to temperature for its days or week of use. None of this seems as though it is well enough understood to have a "calculator" involved.

I would vacuum pack, regardless of whether you decide to do whole bags or divide into portions. I would not bother if the coffee was sold in hermetic, purged bags. As for the so-called one way valves, I've run simple tests on a number of them. IMHO, they are not much better than a simple pinprick. Of the dozens I tested at random, only one actually worked as one way. My test procedure was to fill the bags and seal them, then exhaust the air through the valve with a small vacuum. Although you happen to have a few bags that apparently have self sealed during the flight, I would not rely on that seal staying intact for long.

Yes, as someone pointed out, it sure seems that only two out of the 29 valves are working in a single direction only (the ones that turned my bags into "vacuum packed" bags).

I don't think the airplane effect can be counted on to decide which valves are "good" and which aren't. The degree to which they are vacuumed (an airplane is pressurized to about 0.75atm) depends on how much gas they contained to start with and also how they are packed in your luggage. The pressure in those bags, assuming the valves work, will also be variable. And if the coffee is fresh enough there will be new CO2 released into the bag.

If you seal a bag and evacuate it, like Nunas described, then what? Wait to see if it reinflates? You could have a slow leak but not see any external change. You could cut a valve out of a bag and try to suck through the inside part of the valve. But again, a slow enough leak might not be noticeable. Also, a valve might behave differently depending on conditions (e.g. in the freezer).

If it were me I'd just tape over the valves and optionally put them each bag in a ziplock. I only bother with repackaging and vac sealing when dividing into portions; or if I bought enough to last longer than a couple of months or so. But it won't hurt to do it. It just takes some time and a little money.

jpender wrote:<snip>If you seal a bag and evacuate it, like Nunas described, then what? Wait to see if it reinflates? You could have a slow leak but not see any external change. You could cut a valve out of a bag and try to suck through the inside part of the valve. But again, a slow enough leak might not be noticeable. Also, a valve might behave differently depending on conditions (e.g. in the freezer). If it were me I'd just tape over the valves and optionally put them each bag in a ziplock. I only bother with repackaging and vac sealing when dividing into portions; or if I bought enough to last longer than a couple of months or so. But it won't hurt to do it. It just takes some time and a little money.

I guess I wasn't clear enough, John. I'm definitely not advocating using a vacuum to evacuate the bags and then see if they leak. They'll leak! When I said vacuum seal, I meant vacuum sealing the beans or a bag of beans in a proper bag with a vacuum sealing machine. Although, now that you mention using a bit of tape to seal the valve, I guess that would work too. I have not bought beans in bulk for many years, as I roast my own about every week to ten days...solves the issue for me

Definitely not a "test" for me either, but clear evidence that those valves aren't to be relied on to keep air out.

@Nunas: I took what you were saying to mean that you did that as a test, just to get a rough idea of how reliable the valves are.

I think that it's probably not easy to tell other than when a valve is completely failing. Consider that the cap on a bottle of beer can allow oxygen to enter, even though the bottle is pressurized with CO2. These inexpensive "one-way" valves on coffee bags can't really be that great, maybe just better than nothing. Actually, come to think of it, nothing (as in no valve at all) might actually be better. How often would a bag without a valve explode?