This is a question which we get from time to time, and we can say with the utmost confidence that it is virtually impossible for your wine juice to become mouldy in such a short period of time. What you are in fact seeing is the beginning of the normal fermentation process of wine. At the start of the fermentation process the yeast becomes very active and the wine may even have the appearance of boiling.
Sometimes however it is not that active and the surface of the wine must looks all greyish-brown and bubbly; in fact it looks like a swamp or a bog. In red wines you may not see the colour, but the appearance is the same – just like a bog. There is also a sharp, almost disagreeable odour which is produced by the fermenting yeast. It is, in fact, carbon dioxide which is a natural by-product of fermentation.
The grayish colour is due to the bentonite which you may have put into your must to help fermentation and clearing, and the yeast which is beginning to die off as the alcohol level begins to rise. There is nothing wrong with wine which has this appearance. Often you don’t see this because you are not looking at the right time. By the time most of us look at the wine juice, this stage has passed and what we may see is a ring of grayish muddy looking stuff around the pail and on the underside of the lid or plastic sheet that you have used to cover the pail.
Posted in: Wine