The type of miso that you want to make will determine the salt content you need to use.
Salty misos typically contain 12 – 15% salt. These misos take a year or more to mature; developing a deep, complex flavour. The high salt content means the can be kept indefinitely at room temperature and they will continue to mature, getting better with age. They have a powerful flavour, so not much is needed to add that umami kick to a dish. These misos are best suited to making glazes and marinades, but also make fantastic soups and stocks.
Sweet misos typically contain 6-8% salt. These misos have a more delicate flavour and are normally only take a few weeks/months to reach full maturity. Their low salt content mean that they need to be refrigerated once ready. Sweet misos are best for making soups, salad dressings or sauces.
There are also many misos that fall between these two types – combining the best of both worlds!
The majority of reactions that take place in a maturing miso are anaerobic (do not require oxygen), but a small number of reactions do require air.
For this reason we recommend that 90% of the miso’s surface is covered with weights, leaving a small area open (only covered with salt), to allow gases to escape. If these gases cannot escape, they can build up and cause other off flavours to develop.
To prevent insects or other pests from contaminating the miso a muslin or cotton fabric should be secured across the top with an elastic band or string.
Yes, a small amount of lacto fermentation happens within a maturing miso. This creates small bubbles of carbon dioxide. This is why it is important to put a weight on top of misos that are maturing for longer than 2 months (see question below)
Bad bacteria can thrive if areas of miso are exposed to the air. This is why it is important to squash all the air out of a miso when you make it. Bubbles can also form due to lacto fermentation, so it is important they are removed as soon as they form.
A weight should be added to any miso that is maturing for longer than 2 months. There is no harm in adding them to shorter ferments too.
The weight should be at least 25% as heavy as the miso being made. For example, use a 500g weight if making 2kg of miso.
Any salt can be used to make miso, but ionised salts or those containing anti-caking agents should be avoided, if possible, as these inhibit fermentation.
You should also be careful if using large salt crystals, as these can remain undissolved in the miso. This leads to areas of the miso being under salted. We recommend using a finely ground, natural salt, like Droitwich Sprinkling Salt.
It’s normal for small amounts of alcohol to be formed within a miso, but if you find that the miso is becoming very alcoholic you have too much yeast present. This problem is more prevalent when the miso is stored at a warmer temperature.
To prevent yeasts from becoming dominant within the miso, add more salt. Yeasts aren’t very tolerant of salt, so by mixing more salt into the miso and moving it to a cooler temperature the balance should be restored to the miso.
If you have too much alcohol in your miso (see above) the alcohol can react with acetic acid to form ethyl acetate – a compound that smells of nail varnish remover. The remedy is the same as for too much alcohol in your miso – stir in more salt and move it to a cooler temperature.
The amount will vary depending on the exact conditions in which you make the miso. 1 to 2 % alcohol has been found in home-made miso. If you are at all concerned about consuming alcohol, just ensure the miso is heated to 70°C before eating, as this will ensure the alcohol evaporates.
When the miso comes into contact with air, oxidation can occur. This is completely harmless, but can affect the flavour so just remove this portion if you don’t like the taste.
If you have any more questions about making miso, please leave a question in the comments and we’ll do our best to answer it.