Harvest has arrived in Napa. Right now, all up and down the valley grapes are being received and processed. We crush the grapes and ferment the juice. The fermentation process is performed by our friends the yeast organisms. Like us, yeast cells like to be warm and well fed. When yeast cells are not well fed they can get stressed and produce off-odors or lack the energy to finish fermentation. Yeast requires these nitrogen components to grow and if it is not readily available then they break down amino acids to get it. Some of these amino acids contain sulfur groups that are released when the amino acids are broken down, which is why low nitrogen containing juice can give off sulfur smells. To ensure that that the yeast has enough nutrient supply to complete fermentation and not be stressed we test for YAN or yeast assimilable nitrogen.

The YAN has two components. The first component is the ammonium level and the second component is the NOPA, which measures the assimilable amino acids in the grape juice. What this all means is that, these two components make-up the available building blocks of the yeast. These building blocks go together to form proteins which further go together to produce cell walls, enzymes, etcetera.

We test the YAN by using an enzymatic test that uses ultra-violet light to determine a change in the reaction chamber. Enzymes are organic catalysts that speed up chemical reactions. These reactions cause a color change that is measured by our ultra violet- visible light meter which is called a spectrophotometer.

After we get our results we then add the optimal amount of yeast nutrients at various intervals of the yeasts’ life cycle, to maximize their healthy growth and fermentation of juice. This is the beginning in our facility of what can be a multi-year process; from fermentation to full maturation of the wine.