A sip of context: In one of our Oenology modules we are learning about the biochemical makeup of grape juice and how the yeast is built to combat the difficult environment it’s placed in and still manages to produce the glorious product of wine.
Jerry, an unsuspecting Saccharomyces cerevisiae yeast, was produced the normal way, along with all his 1×106 brothers was frozen and stored. A happy life, he was content to sit and wait until his strain was chosen to go to the cellar. Some called the cellar the Promised land, others called it the battle field. Either way Jerry knew his life would never be the same, he was no longer allowed to sit idly by; he would have to live up to his potential.
The protective bag he had once called home was cut open; a giant scoop bore down on him and a sample of his kin. They were then placed in a warm liquid, all the while enjoying the change in temperature. A strange powder was pored over them, suddenly the cells were filled with energy, Jerry thought to himself ‘this must be that energetic yeast nutrient we’ve heard about’. A larger yeast cell made his presence known: “Attention cells! You are no longer in your small protective bags anymore! You are now part of a population, we are expected to expand and grow for the next 10 days, but first a test. You will be exposed to the harshest environment you could ever imagine; Sauvignon Blanc. We are talking a pH of 2.9 and an acidity of 10.11 g/l. There will be sulphur, there will be other microbes that want to take our supplies and through all of this, if we succeed we will die anyway. This is your chance to shine, this is your purpose, are you ready!?”
Jerry was tentative, however the yeast nutrient made him feel strong; he could feel his cell membrane expanding and his size increasing. He was ready.
The first wave of Sauvignon Blanc was on its way. Still exposed to the heat, Jerry could feel his energy increasing, he watched the skies as the Sauvignon blanc rained down on them. A couple of his brothers fell as soon as the juice touched them. Others wavered a little; however the majority of them, including Jerry, remained strong. The bigger cell was right, the conditions were harsher than imaginable, but in same environment there was plenty of nitrogen and sugar for Jerry to use.
Glucose, a beautiful six carbon chain emerged in front of Jerry, he actively transported it into his system, hoping it would form something none toxic. That was the catch 22, he had to consume it to survive, but what it produced all depended on his internal environment. On the horizon he spotted an amino acid, it wasn’t proline so he knew he could consume it. He couldn’t believe his luck, amino acids were in high demand now that the population had expanded to a little over 1×107 and showed few signs of slowing down. Actively he consumed the amino acid; fortunately it was a branch chain amino acid; meaning it would go through transamination and oxidation to form a fatty acid, from there it would react with ethanol and become something beautiful: an ethyl ester.
Thinking about the lovely smell surrounding him, he was grateful that some of the ethanol was consumed to make it. The ethanol had been increasing at an alarming rate, so much so that the microbes he once considered competition had already died off.
A day later the population had already reached 1×108 cells. Nitrogen was in very short supply and the sugar reserves were depleting. The environment had become harsher, the sugar that once sustained them had been converted into alcohol, and the only way to get some nitrogen was to scavenge from the husk of what was once a yeast cell. Everywhere Jerry turned he saw one of his kin, trying to absorb as much sugar as possible, with the hope it would turn into a flavour compound and not something toxic.
Jerry began feeling weak; he could no longer oxidize fatty acids to expand his membrane and walls. The acid levels were high and the sugar levels were low. Glycerol made movement difficult and the ethanol levels started to get to him.
All though the environment was harsh, it smelt nice, sort of like cut grass on a summer’s day mixed with dashes of stone fruit and citrus. This is what that big cell must have been talking about, what Jerry and his clan have been working for, for all this time. Jerry started to sink to the bottom and settled in a layer of husks, although this was the end he was satisfied that he had achieved his purpose: he created a fantastic wine, and his legacy would last for months or even years to come.