(a) Natural wine production. Water may be used to flush equipment during the crushing process or to facilitate fermentation but the density of the juice may not be reduced below 22 degrees Brix. However, if the juice is already less than 23 degrees Brix, the use of water to flush equipment or facilitate fermentation is limited to a juice density reduction of no more than one degree Brix. At the start of fermentation no material may be added except water, sugar, concentrated fruit juice from the same kind of fruit, malo-lactic bacteria, yeast or yeast cultures grown in juice of the same kind of fruit, and yeast foods, sterilizing agents, precipitating agents or other approved fermentation adjuncts. Water may be used to rehydrate yeast to a maximum to two gallons of water for each pound of yeast; however, except for an operation involving the preparation of a yeast culture starter and must mixture for later use in initiating fermentation, the maximum volume increase of the juice after the addition of rehydrated yeast is limited to 0.5 percent. After fermentation natural wines may be blended with each other only if produced from the same kind of fruit.

(b) Determination of wine produced. Upon completion of fermentation or removal from the fermenter, the volume of wine will be accurately determined, recorded and reported on TTB F 5120.17, Report of Bonded Wine Premises Operations, as wine produced. Any wine or juice remaining in fermentation tanks at the end of the reporting period will be recorded and reported on TTB F 5120.17.