A magnum holds 1.5 litres, exactly two standard bottles, and it ages roughly half as fast as either of them. The reason is not the glass. A magnum has the same neck and the same cork as a 750ml bottle, so it traps about the same pocket of air, but with twice as much wine underneath it. Each mouthful sees half the oxygen.
The same rule runs in reverse, which is why a half bottle is always older than its age.
Why oxygen is the whole mechanism
Every sealed bottle has a gap between the wine and the cork. That gap holds a little oxygen, and a tiny amount more seeps past the cork over the years.
Oxygen is what drives a wine forward. It softens tannin, it turns primary fruit into something savoury and secondary, and eventually it takes the wine past its best and out the other side. Slow the oxygen and you slow all three.
Nothing about the wine itself changes in a magnum. It is the same wine from the same tank on the same day. It simply meets its future more slowly.
The formats, and the ones worth knowing
| Name | Volume | Standard bottles |
|---|---|---|
| Half bottle | 375ml | 0.5 |
| Standard | 750ml | 1 |
| Magnum | 1.5 litres | 2 |
| Double magnum | 3 litres | 4 |
| Imperial | 6 litres | 8 |
Past the magnum the names multiply and the practicality collapses. A six-litre bottle weighs more than a small child, will not fit in a rack, and needs a table of people ready to finish it in one sitting. Magnums are the largest format a normal house can actually use.
When a magnum is worth buying
Not always, and the honest answer depends on what you are going to do with it.
- For a wine you intend to keep, yes. If a wine has ten years in front of it, the format genuinely changes the outcome.
- For a wine you will drink this year, no. The ageing advantage needs years to show. Buy the standard bottles.
- For a table of six or more, yes. One magnum poured around a table is a different event to two bottles opened twenty minutes apart. It is the bottle you put in the middle of the table, not in the fridge door.
- For a gift with a date on it, yes. A magnum of a birth-year or anniversary wine is the one format still worth opening when the date comes round.
- For two people on a Tuesday, no. You will not finish it, and a magnum keeps no better than a bottle once it is open.
Storing and opening one
Lie it down, like any cork-sealed bottle, so the cork stays wet. Most domestic wine racks will not take a magnum, so plan for it: a magnum on its side on a cool shelf, out of the light, is better than a magnum standing upright in a rack it does not fit.
Opening one takes a little more care simply because of the weight. Stand it up a day before if it is old enough to have thrown a deposit, and decant it properly rather than pouring from a three-kilogram bottle across a full table. Our guidance on how long to decant applies unchanged: the format slows the ageing, it does not change what the wine needs on the night.
Magnums at Boschkloof
We bottle magnums in small numbers and only from wines we think are worth keeping, which is why they come and go rather than sitting on the shelf all year.
They are not sold at retail. The only place to get one is from us, and when a release is gone it is gone, because the next one is a different wine from a different harvest rather than a repeat of the same thing.
One question to ask before you buy one
Where will it be in five years?
If the answer is a specific shelf, a specific occasion or a specific person, buy the magnum, because the format is doing real work for you between now and then. If the answer is that you are not sure, buy six standard bottles of the same wine instead. You will drink one a year and learn what it becomes, which is the cheaper and more interesting version of the same experiment. The range is here, and a magnum release shows up there first.