Slow fermented grape must (druiwe mos)

Must is basically crushed grape mush that has been allowed to ferment for a couple of days. In fact, the Romans called it vinum mustum, which means “young wine”. Must (called mos in Afrikaans) is also the rising agent used for traditional South African mosbolletjie rusks, resulting in delicate rusks with a beautiful, subtle flavour.

Must is produced during the early stages of winemaking, by crushing grapes juice, seeds, skins, and all, and leaving it to ferment. During fermentation, which can take up to five days, the seeds, skins, and stems will start rising to the top, after which the pomace (all the solid bits) is removed.

If you want must for mosbolletjies, the ideal grape to use for must would be sweet Hanepoot, also known as the Muscat or Alexandria grape. Hanepoot was cultivated on the old wine farms in the Western Cape of South-Africa, after the French Huguenots settled in the Cape of Good Hope. During Harvest season, they used must as leavener (raising agent) for baking. 

Having said that, just about any organic grapes with seeds will do the job. Dark or red grapes will give it some colour, but whatever grows in your or your neighbour’s backyard is perfect. 

The supermarket’s fancy table grapes won’t work though. They are often subjected to processes like irradiation, which kills the yeast that should start the fermentation. Susan, a winemaker in California, told me that they do not wash their grapes; they simply remove the stems, leaves, and bad grapes, crust the lot, and stir it every day, which prevents it from rotting.

If you know a winemaker, you can possibly ask them for some must, but because we don’t know a local wine farmer, we make our own must. We simply ask neighbours and friends who have grapes in their backyards for some of their grapes. This is how we make our must:


2 litres (about 1 kg) organic grapes that are not shop-bought, and unwashed, so that they stil have a dusting of white yeast on their skins.

This will yield about 450 ml of must, depending on the type of grapes.


  1. Throw any bad grapes out, but keep the stems. Avoid washing them if you can. A light rinse might be required to wash off any dirt, but don't rub them dry. The main thing is not to wash of the yeasty white powder that covers each grape. 
  2. Place the grapes in a large container. You need at least a 2-litre container for 1 kg of grapes. Mash the grapes and mix the juice, skins, seeds, and stems together. 
  3. Cover with cheesecloth and allow it to ferment at room temperature, for about 2 to 5 days. The weather and temperature will determine the speed of the fermentation.
  4. Stir it twice every day. The important thing is to work the top layer back into the mixture. This prevents mould from forming. The grape juice will start to become more and more fizzy, and will smell a bit like young wine. It is not a great smell, but not a bad one either.
  5. When the skins, seeds, and stems have formed a fairly solid layer on top, and the grape juice is so fizzy that lots of foam forms when you stir the mixture, as shown on the photo above, you can strain it with a sieve. You now have grape must. The solid residue (the pomace) can go into your compost heap.


The must should be mid-ferment when used. 

If we had the necessary equipment to measure the sugar level, it would be ready once it reaches about 17 Balling. (Balling is a density scale for measuring sugar content in water solutions.)

We simply go with our gut feeling though, which means that we ferment the must for three to five days, until it is fizzy and smells quite intense. Like most things in life the best way to learn is by trial and error.