How to make Vegemite at home

No, you need industrial machinery.

Part of the manufacturing process of producing Vegemite involves using a centrifuge to separate out the yeast cell membranes from the rest of the product. As a result, without access to such a centrifuge, it is not possible to make Vegemite.

Here is a description of the process I found through a Google search:

Spent brewer's yeast is sieved to get rid of hop resins, and washed to remove bitter tastes. Then it is suspended in water at a temperature greater than 37 C with no nutrients: the yeast cells die, and vitamins and minerals leach out. Then the proteolytic (protein-splitting) enzymes take over, breaking the yeast proteins down into smaller water-soluble fragments, which also leach out. The yeast cell membrane is unruptured during this time, and can be removed by centrifuging. The clear light brown liquid is then concentrated under a vacuum to a thick paste (the vacuum helps preserve flavours and vitamin B1, thiamine). It is seasoned with salt, and a small proportion of celery and onion extracts to increase the palatability.

You could instead try making your own Marmite.

Excerpts copied from MsMarmiteLover's Blog - HOW TO MAKE YOUR OWN MARMITE
Please read the whole piece for more background.

My role as MsMarmitelover meant that I was able to go straight to the top: after some negotiation with the Marmite authorities, I was given a telephone date with St.John O. Skelton, Master Blender of the Marmarati Order or, more prosaically, Quality and Innovation Expert at the Marmite factory in Burton On Trent. He was willing to help me but darkly intimated that making Marmite was “dangerous and hard to control”.

RECIPE FOR HOME MADE MARMITE:

A litre of Brewer’s yeast (top fermentation from a brewery) A little sea salt 1 onion, diced 2 carrots, diced 1 turnip, diced 1/2 celery stick, diced

1. Put a litre of brewer’s yeast with a little salt, in a bain-marie. Simmer at blood heat, 30 to 40 ºc for ten hours or overnight.
2. Then simmer this mixture at 50 to 60 º c for 2 to 3 hours.
3. Boil at low temperature 90ºc for half an hour. (In the factory they have a special machine for this, or you could ascend a mountain of 10,000ft, to achieve low altitude boiling)
4. Filter though coffee papers or a sieve and cheesecloth
5. Let it cool for a day or so. It separates further.
6. Filter again.

7. You then want to convert it to a paste. This is best achieved by putting it in a large flat pan and simmering. On an Aga, you can simply leave the pan on the lid for a few hours. Keep an eye on the mixture.

8. Meanwhile boil up all the vegetables until they are cooked. Strain off the liquid and incorporate into the Marmite paste.

9. Let the mixture reduce into a Marmite like texture. Do not allow it to burn: “We do not want to develop caramel notes” warned St.John.

The entire process takes about ten days. This home-made Marmite admittedly tastes different, like something German and healthy in a tube. Lacking the specialist equipment to ‘debitter’ the yeast, it will have beerier flavours, rather like the Guinness or XO Marmite.
It was a comfort to know that I could, in a pinch or say, a calamitous event such a terrorist attack on the Marmite factory, DIY my own Marmite. But realistically, I’ll probably stick to shop-bought.

Update: the main problem was the bitterness of the brewing yeast. The solution is to wash the yeast. You achieve this by putting the top fermentation in a jar full of water. Eventually the yeast will settle on the bottom of the jar. Pour off the water and fill the jar again with fresh water. Do this several times to wash the yeast. Then follow the recipe above.