Mix the water and salt together. Stir to dissolve the salt.
In a glass jar, place the garlic, mustard seeds, black peppercorn, fresh dill in the bottom.
Add cherry tomatoes on top of the herbs and spices in the glass jar. Pour the salt water into the jar to cover the cherry tomatoes.
Seal the jar with a lid, and let them ferment in a dark spot for about 7 days, until they reach the desired flavour and softness. The tomatoes will start to produce bubbles when fermentation begins. Open the jar daily to release gas.
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Notes
You can taste the cherry tomatoes around 5 to 7 days of fermentation. The longer they ferment, the more flavours they will take on from the brine, and the softer they will become. If they haven't reached the flavour and texture you desire, you can ferment them for a few days longer and continue checking on them. I find the cherry tomatoes with thicker skin require a longer fermentation time. If the cherry tomatoes are fermented for too long, they begin to crack and break down into the brine. The ideal window to eat these cherry tomatoes is when they have soften, but before they begin to fall apart. Store the fermented cherry tomatoes in the brine, in sealed glass jars, inside the fridge.