Cold soak or the far more technical and scary sounding “cold maceration” is a pre-fermentation process to extract colour and flavour from fruit. Its an easy enough process plonking your fruit in cold water for a while before you add the yeast.
Skins, particularly in berries have most of the flavour trapped in the skins rather than the juice that will eventually be squeezed from them. Soaking them allows the flavour and colour to leech into the surrounding water extending aqueous contact during fermentation. Elderberry, gooseberry, red & blackcurrants and blueberries are all fruit that can be aided.
After foraging (or buying) the fruit I usually freeze it for a week. This breaks down the pectin by up to half reducing the potential haze that could develop during fermentation and also breaks down cell walls allowing more juice to be extracted. Even if you are not cold soaking this is recommended for sloe, haw and rosehip wines.
A day before you want to start the cold soak boil some water to sterilize it, cover and then set aside to cool. On the day get a nice sized food grade tub or stainless steel pan and crush one campden tablet and sprinkling on the base. This is used to kill the wild yeasts and any remaining bacteria that might be present on the skins. Pour in the fruit, then as much of the water as you possibly can. It is important not to squeeze the fruit as you want to affect the skins as much and seeds as little as possible. The fruit should at least be totally covered but the more water the better.. Keep a note of how much water you add as you will need to take this into account when you eventually start to make your wine. Cover with cling film so that little air is in contact with the water to stop the chance of oxidation then put that in your fridge.
It may take 24hours for the fruit to thaw and the actual process of the soak to start taking effect. The fridge will keep it at about 7 degrees C well below the maximum temperature for cold maceration. If it did rise to about 15 degrees there is a chance that spoilage microbes and wild yeast could become active.
There is no right or wrong in the duration of a cold soak some leave for 2 days like a white wine and others can leave a lot longer up to 10 days in extreme cases. It is all down to personal choice. Generally I leave gooseberries for 2, unless I am making a sherry when it will be longer. Elderberries get 5 or 6 days as do blueberries.
Stir once a day with a sterilised ladle. This will agitate the fruit to allow decent water contact. As you open each day you will notice the colour become deeper and the aroma of the fruit becomes more apparent. Blue berries tend to swell and burst too. Once done give the fruit a good squeeze to break them open – don’t forget to wash your hands thoroughly! Leave covered in the pan/container over night to naturally get to room temperature before continuing with the remainder of the recipe. This is also a good time to add pectic enzyme to destroy any remaining pectin.
There is obviously the extended contact between the skins and water allowing more flavour to be extracted but there is also the benefit of choosing what flavours to extract. A cold soak is an aqueous extraction going for the flavour and aroma compounds in the fruit but leaving harsher tannins that are far more likely to be extracted by the alcohol created during fermentation. This means you can tailor the cold soak and then fermenting soak removing the fruit before too much tannin has been liberated by the fermented ethanol. Harsher tannins in skins take the longest to extract via ethanol and the harshest tannins that are present in seeds get as little contact as possible. This is particularly useful when making a lighter tasting Elderberry wine allowing less bottle ageing.
THE DEADED RHUBARB BATH
One fruit to never ever ever cold soak is rhubarb as a cold soak will liberate more acid from the fruit. As most fruit wines get citric acid or lemon juice added this is no problem, rhubarb contains enough or too much acid so a soak will simply exacerbate this issue. For rhubarb do not even introduce it to your must. Chop it as fine as you can by hand, cover it in your allotted sugar for 3 days stirring once a day. The juice will soak into the sugar so you can then dissolve it into the must and discard the flesh.
The idea of using a cold soak was originally inspired this page Hank Shaw at HUNTER ANGLER FARMER COOK