Once you have added your yeast to the juice, it is time to think about giving it some nutrients. Yeast like nitrogen to help them keep growing and functioning. Without proper nutrition, the yeast will be strained and change their metabolic function. This can cause such things as production of hydrogen sulfide (rotten egg smell), sluggish fermentations, or even cause a fermentation to stop. Stopped fermentations are notoriously difficult to restart. There are numerous yeast nutrients on the market. The main nitrogen ingredient is diammonium phosphate or DAP. Many winemakers use only DAP. Others use combination nutrients with names like Super Food, GoFerm, Fermaid, Opti-Red and such. These have other vitamins and minerals in addition to DAP and are, of course, highly touted by the manufacturers. I have used some of them on occasion, but, for the most part I use just DAP in my white wines. For red wine, I use Opti-Red, which I will discuss in more detail when we get to red wine fermentation.
Additions of nutrients should be dependent on the amount of nitrogen already in your juice. The nitrogen content must be tested in a lab. However, many people do not have access to this testing procedure or the ability to send it to a lab and get it back in time to make additions. My rule of thumb, which may really be in “left field” is to add 5 pounds per thousand gallons. As I have said many times before in this blog, this has worked for me. However, I read recently that the addition of 2.5 pounds per 1000 gallons is sufficient and so I may try cutting down the amount I use this harvest season. It is best to add the nutrient in two stages, half the total amount each time, once at the beginning of fermentation and once mid-fermentation. This product is dissolved in a bit of water before addition, just enough to get it to dissolve. If you want to, you can make your first addition of this nutrient when you add your yeast.