Alan I agree the pressure differential is small though I wouldn’t dismiss it when coupled with the extreme cold of a cargo hold on a long haul flight with unserviceable heating or if the bags are put into a unpressurized/unheated baulk hold which you have on some aircraft. The later could be where the real problems are stemming from.
What is the effect of temperature and pressure on a liquid? Wouldn’t it’s volume increase if significantly cooled? Now add a fast descent and warming…
This is from IATA-
1.1
.This note sets value, drop to 68 kPa and it covers transportation in pressurized cargo holds only, which equal 3 000 meters flight altitude in a non-pressurized cargo hold. Modern cargo aircraft with non-pressurized cargo holds climb up to 10 000 meters, and in this case the pressure drop in the cargo holds down to 24 kPa. This pressure reduction will tend to cause discharge of liquid contents or bursting of the receptacles or packaging during flight, because the receptacles or packagings are tested for transport in pressurized cargo holds only. To prevent this risk we propose to add this information to Part 4, Introductory Notes, Note 3.
Due to altitude, pressure reductions will be encountered under flight conditions which may in extreme conditions for aircraft with pressurized cargo holds be of the order of 68 kPa and be of the order of 24 kPa in aircraft with non-pressurized cargo holds. Since receptacles or packagings will generally be filled at normal atmospheric pressure of approximately 100 kPa, these pressure reductions will tend to cause discharge of liquid contents or bursting of the receptacles or packagings during flight, unless each receptacle or packaging and its closures meet the packaging test requirements for transport in pressurized cargo holds. In the case of transport in non-pressurized cargo holds, each receptacle or packaging is to be able to meet its pressure reduction value.
Unless it freezes, the density of water actually increases as temperature drops, down to about 4 degrees if I recall - meaning that the volume will decrease, not increase. You have more experience than I do, but I’ve checked wine in luggage dozens of times, and never ever had a problem.
This, modified by Jamie’s comment re: different aircraft types. I’ve had zero problems with wine in the luggage hold. 
Ditto, except maybe even more than dozens of times. If there is any slight risk of the occasional bottle being affected (which I’ve never experienced, but let’s say for the sake of argument there is some small risk), it’s still bound to be far smaller than the risk that you get to your destination and don’t have great wine to drink while you’re there.
I’ve taken hundreds of bottles on long haul (20+ hours) flights and never had issues. The planes have typically been 747s or A380s
By the way, most modern bottling lines extract a vacuum from the bottle as the cork is inserted. So for some time the pressure inside the bottle will be less than the atmospheric pressure.
This has happened to me at least a few times with newly released DRCs. Nothing major but small seepage. When I ship DRCs, I now request the bottle to be wrapped. I hope your wine arrive safely.
Not to do with pressure changes, but be aware of your stopovers. They take the luggage out of the plane, and it sits outside and it sits in a tractor until it gets loaded onto your next flight.
We came back from CA with a wine check 2 weeks ago. Our connecting flight in Phoenix was canceled, so we had a 4 hour wait until our flight. It was 98 degrees when we landed and we were pretty worried about our wine.
We did put some of those instant cold packs inside the insulated box before we left. They were no longer cold when we got home, but it seems to have done the trick. I opened a bottle of Viognier from that case last night and it was ok.
DRC and Leroy are famous for leaking because they tend to over-fill the bottles, ie there is little or no head space.
-Al
To follow up, in case it wasn’t clear, the lack of head space makes the bottle prone to leaking (or the cork moving) with even modest changes in temperature.
-Al
I find this thread really helpful. I have flown with wine a bunch of times both domestically and overseas and never had a problem. Recently I had a bottle of SQN shipped cross country via 2 day delivery and the cork pushed out. I suspect it was a combination of lack of head space because I think SQN fills pretty high into the neck and possibly the type of plane flown. I imagine cargo planes aren’t worried about carrying people or pets and therefore don’t worry quite as much about pressure changes in the hold.
Odds are if the fill is high and the cork has pushed out, the wine was either too warm or frozen at some point. Doubtful it could have anything to do with air pressure.
Flew last night from SFO to JFK with two cases in the hold via Wine Check and a few more bottles packed in a suitcase. All arrived with no issue, including a sparkler.
For young wines, you are probably fine. However I know of a specific situation where a gentleman checked a particularly expensive bottle ($5000+) that was north of 40 years old on an overseas flight. Bottle was pristine with no signs of a bad cork before, however after the flight it was seeping. For a reference point, the airlines do not recommend checking wine, and insurance/credit card companies take note of that.
I would like to see a little more science before pressure differentials are entirely dismissed. Especially when the change in pressure is coupled with a significant temperature change. For instance, how will the cork behave as the wine approaches the freezing point and the aircraft’s cabin altitude is 8000 ft or higher as per a cargo aircraft scenario? As a wine approaches the freezing point where it expands in volume, the cork must have some vulnerability to movement, and I’m guessing that the pressure differential could come into play to at least some degree.
My advice is again, to insulate as if your wine will be put in a freezer or left on a 40 degree tarmac- or both as is the not unlikely chance with freighter aircraft. Most airlines I have worked with have a lost squadron of aging hulks configured for freighter operations. These old 747’s are notoriously unreliable and often they would break down at the half way mark of their journey to Asia on the hot tarmacs of the Middle East. So a wine heats up and then climbs back up for a 12 hour slow freeze at a cabin altitude of 8000 ft + on a long journey to Asia.
I don’t know about the USA, but I choose to ship via sea in air conditioned containers and try to avoid air freight when shipping from Europe to Asia.
I have no science. Just experiential results. I’ve traveled a fair bit checking cases of wines to final destination. Always using styro containers. A few months ago, a case of wine to the Virgin Islands. No problem. Today, a case of wine from MSP to Vermont. Too early to tell about the latter case in aggregate, but a 2000 Taittinger champagne opened tonight had no ill effects. Never had a problem with a cork being pushed or pulled. My only caveat, and it has nothing to do with pressurization, is the jostling involved with older, sediment-laden wines.