Fermaid AT: professional winemaking yeast nutrient. This is the product that professional wineries use and has been developed specifically for the New Zealand and Australian wine industries. This is a relatively new product and is more scientifically advanced than other nutrients available to home winemakers.
Dosage is 1.5g per 5 litres (1 gallon) of wine (1/4 teaspoon is about right). Note this is far less than dosage amounts for other nutrients.
For low YAN (yeast assimilable nitrogen) environments like spirits washes, you can use a dosage of up to 1g/L.
Ideally use in conjunction with GO-FERM® Protect; but if you are going to use one or the other, then choose Fermaid AT.
For home winemaking it is recommended that half of the Fermaid AT should be added before pitching yeast and the other half about 1/3 of the way through ferment. The Fermaid AT will provide organic and inorganic nitrogen along with a boost of minor nutrients and vitamins.
Fermaid AT (especially if used in conjunction with GO-FERM® Protect) will be far more reliable than DAP (diammonium phosphate), Vitamin B1 (Thiamin) or Tronozymol. None of those nutrients have amino nitrogen (Fermaid AT does) which is essential later in the fermentation for preventing stuck ferments. Straight DAP will make the yeast grow and perform well at the start and middle of the ferment. However, because the yeast cannot store it (like they can amino nitrogen) there will be none available internally at the end of ferment when the yeast are unable to take up further nutrients.