Vacuum limits on Demijohns?

[Ochimus]

Can anyone advise what level of Vacuum 5 litre and 30 litre demijohns can tolerate?

At present I degas my wine by taking off the lid and stirring the brew several times a day for five minutes a time over four days using a drill and wand.

But various clips and articles on the web show wine in a demijohn being degassed comprehensively in ten minutes, using a small pump to create a vacuum in the headspace, forcing the CO2 bubbles to rise AND without exposing the product to air

Unfortunately none of them explain what 'level' of vacuum a demijohn can take before it cracks or even implodes or explodes?

Last thing I need is a cracking sound followed by a wine Tsunami surging through the garage, worse still being injured by flying glass as the container shatters, or even creating a wine fountain when I unlock the vacuum pipe from the container!

I have asked two major Home Brew companies, but neither of them have any idea, and both said this was the first enquiry they had actually received on this topic.

Appreciate any guidance the members can give?.

Ochimus

 

[Agentgonzo]

The glass of demijohns is pretty thick. And it is circular and has a rounded top and corners. I would expect you would be able to get a total vacuum inside the demijohn and it would withstand it.

A total vacuum will result in 1 atmosphere of pressure (inwards). Standard bottles can withstand 2-4 atmospheres of pressure (albeit outwards), champagne bottles upwards of 6 atmospheres. A demijohn has thicker walls than all of those

 

[Chippy_Tea]

I wouldn't risk it, a degassing wand will do the job in a minute How to degas wine with a home made degassing wand

 

[MashBag]

There a difference between an empty one dvd a full one.

I funny think you will get a definitive answer.

I few thigs spring to mind...
Stand in a 'kitchen' clean plastic trug.
Contained the vino & the glass.
Glass does not float. So it is possible to rack or filter if you do have a breakage.

Degassing is also unnecessary, time degasses a wine perfectly. Red wine is at its best with 800ppm co2 for flavour and mouthfeel.

 

[Chippy_Tea]

Degassing is also unnecessary, time degasses a wine perfectly. Red wine is at its best with 800ppm co2 for flavour and mouthfeel

While I agree wine will Degas's (and clear) over time if you want to drink it fairly soon after it's finished fermenting you need to Degas it to aid clearing.

 

[tigertim]

Generally speaking, if a container isn't vacuum rated, I wouldn't personally want to risk drawing a vacuum in it. The design of the vessel is critical to withstanding pressure differentials, and the stress exerted is very different between positive and negative pressure. So whilst a champagne bottle can withstand an exceptionally high internal pressure (partly because of its thicker glass relative to its size and inwardly dished base), it may well perform poorly in a vacuum - I wouldn't really fancy trying!

If degassing by vacuum is something you'd like to try, I think it'd possibly be better to acquire a vacuum chamber and place the entire wine-filled demijohn in there. They can be acquired relatively cheaply because of their popularity for degassing epoxy and other resins for optical purposes in art and sculpture.

 

[MashBag]

While I agree wine will Degas's (and clear) over time if you want to drink it falrly soon after it's finished femenntimg you need to Degas it to aid clearing.

I agree, but it does open the door to over degassing, and the wine will taste flat.

Ages ago people used to do it with a vacuvin, just mod a bung to fit. More gentle.

 

[Bernie]

Don't evacuate at all.
I used to supervise research students doing theses in Engineering and I'd ask them at what pressure they'd be able to open the stainless steel door of an evaporator. None ever thought it would be near one atmosphere. In other words, there's quite a lot of force over a largish area even with small pressure differences. Why does this matter? Because that large force can collapse a brittle vessel. Think of a balloon bursting even though the pressure inside is not so great.
A glass vessel may be thick but a sharp scratch or slight crack can initiate the collapse since it's at the sharp edge of the scratch where the stress is greatest. The implosion will be sudden and catastrophic. The shards of this implosion will not collapse to the centre but can continue across. A lab acquaintance I knew had a desiccator implode and the glass buried itself in the wall opposite. Luckily, he had moved out of the way to do other work, just beforehand. Normally, wire mesh netting is placed around glassware if it's under vacuum and not inside a closed fume cupboard.

 

[Chippy_Tea]

I agree, but it does open the door to over degassing, and the wine will taste flat.

I have found one minute total degassing (5 seconds forward - 5 seconds reverse and repeat) does the job enough to allow quick clearing, i wouldn't describe the finished wine as flat so maybe the sweet spot