Hello and welcome to DeerfieldCellarRat.com! If this is you're first visit then allow me to express my gratitude for checking out the site and I hope you enjoy reading. If you're a fan of the site then please accept my sincere apology for leaving you out of the loop for the last week or so. I know some of you are really enjoying following along with the harvest, but as you know it is in full swing by now and you can probably imagine that it has been very hard to find the time to write. But I'm back at the keyboard now so let me fill you in:
Last time I left you with a cliff hangar. Due to my debilitating injury and thanks to doctor's orders I had been reassigned from normal duty and asked to fill a different role. This is what happened: I reported to Robert that the doctor said I was to refrain from using my left hand as much as possible. Our laboratory technician was present at the time and unfortunately for her, Robert, doing some quick thinking, announced that she had a new assistant. Amanda and I glanced at each other, equally surprised at the verdict. I was pleased (as I always am at the prospect of learning something new). I can only guess her feelings about acquiring a new assistant. Truth be told, I have a pretty good idea about it because that was two weeks ago and she got rid of her meddlesome assistant pretty quickly. Ignoring doctor's orders, for better or for worse, I returned to my daily duties as a Cellar Rat, single-handedly conquering each task appointed to me, after only one day of shadowing her in the lab. In that time though I did get to learn how to test the wine for Total Acidity, pH, dissolved oxygen and free sulphur. Acidity is a crucial measurement because having the right amount of acid is critical for producing a balanced wine. I learned that pH is actually not a helpful measurement of acid as is just a buffer that compares the level of acid to the level of base. Dissolved oxygen is the amount of oxygen mixed into the liquid of the wine causing it to oxidize internally in a way. That's why we add the SO2. If you recall it bonds with the O2 to become the neutral SO4. Sometimes it does it's job and there's some left over. That's what the free sulphur test is for.
Even though I haven't been spending much time in the lab I have been spending a lot of time doing something that has a real chemistry feel to it. As you may already know, yeast is the crucial ingredient that transforms grape juice into wine. That amazing, rapidly multiplying, living organism, munches the sugar and produces alcohol. It occurs naturally in the vineyard and because it only takes one yeast cell to create a colony, grape juice left alone will eventually ferment, which is how, I imagine, they discovered wine in the first place. These days though we take a more advanced approach, selecting and adding species of yeast that accommodate specific species of grapes. In fact, we have cultivated yeast so much that we can use different kinds to produce specific flavors. The yeast have fairly unromantic names like "RC212" or "D47". Occasionally a charmer comes along like "Rhone 4700". The process of adding yeast to the juice is called inoculation. Care must be taken during this process because happy yeast makes good wine and if you don't make sure those microscopic buggers are having a good time, they'll make sure to spoil your dinner party. Before you add the yeast you add it's food. Superfood to be precise, a delicious mixture of nutrients and amino acids that prevents the yeast from becoming cannibalistic and consuming the carcasses of cadaverous comrades (please excuse my fit of alliteration). DAP, or diammonium phosphate to be exact, is also added to feed the hungry critters. At this stage tartaric acid is added not for the yeast, but if it is determined more acid is required to balance the flavor. The juice is now ready for the yeast to be added, but first the yeast must be awakened. You see, the yeast is in a dormant state and needs to be activated after it's long hibernation. So water is heated to the exact temperature it likes: 105 degrees Fahrenheit. A catalyst called Go Ferm is added to the water and then the yeast is slowly mixed in. It takes about 15 minutes for the yeast to wake up and after that period a sufficient amount of wine is added to acclimate the yeast to the temperature of the juice it is about to call home. The mixture of water, juice, Go Ferm and yeast turns a phenomenal shade of violet and is then evenly poured over the surface of the bin/tank. The punch down method is insufficient to properly mix the yeast with the wine so we use the pump over technique: With the use of an air pump, juice is sucked from the bottom of the bin and pumped over the top. After fifteen minutes the juice has everything it needsto begin fermenting. The Brix will drop every day from now on and the temperature will rise. Fermentation is an exothermic reaction and the temperature can get up to the low nineties. The reaction produces an incredible amount of CO2. After one to two weeks the juice will have, by definition if not taste, become wine.
Well I hope that this article makes a up for my absence. I promise, readers, another article tomorrow! I'll be talking about pressing the wine after it's finished fermenting!
Every day during harvest, the lab tech goes to each fermenting batch of wine and tests the level of Brix (a measurement of the percentage of sugar). As the wine ferments the Brix steadily drops until it reaches zero, indicating that all of the sugar has been converted by the yeast to alcohol. But occasionally during the fermentation, the chart hanging from the tank where the tech records posts the readings shows the same result day after day. That’s when you know you’re dealing with a stuck fermentation. The yeast has died off, become less active or stopped multiplying. Without treatment, the result would be syrupy sweet juice. It can be scary, but with the right techniques, a skilled winemaker can save the day. Our gold-medal-winning Buchigniani/Garcia Dry Creek Valley Zinfandel gets stuck every year because it comes in at such high Brix.
High Brix means high sugar and sometimes that creates a situation in which the yeast has made so much alcohol that before its finished consuming all the available sugar, the alcohol is high enough to kill the yeast. There are other reasons that primary fermentation can get hung up though. Sometimes the problem is as simple as the tank is too cold for the yeast, and they slow down quit doing their job. Occasionally a harmful bacterium from the vineyard such as Acetobacter or a mold such as Botrytis is producing acetic acids, increasing the volatile acidity and thereby disturbing the yeast. Sometimes there are not enough nutrients in the juice to sustain the yeast. In all cases, as soon as the winemaker has discovered that their wine is stuck, they immediately press the wine off of the skins so that they can better control the process.
Additionally, secondary fermentation (or malolactic fermentation), in which bacteria converts harsh malic acids to softer lactic acids, can outstrip the pace of the yeast. This is often the case with stuck fermentations and the procedure is to let the beneficial bacteria Oeonococcus and Lactobacillus run their course, at which point the primary yeast fermentation can be restored. The wine is then racked off of its lees before restarting the regular fermentation. Rice hulls (which are like the husks of rice grains) are added to neutralize harmful toxins in the juice.
The process of restarting fermentation varies from winemaker to winemaker. At Deerfield we begin by taking some of the wine from the tank and making a mixture of 50% wine, 50% water, fresh yeast, yeast food, and other nutrients which we then allow to start fermenting. This mixture is then added to the tank which is kept at 70⁰F and carefully monitored. When the Brix drops by half of what it was when it became stuck another mixture is prepared. This time the ratio is 75% wine and 25% water. Again when the Brix halves a final mixture is readied. The last mixture includes just wine from the tank and the remaining nutrients the yeast needs. The idea is to slowly acclimate the yeast to the environment of the wine so that it is happy, healthy, and well prepared to do its job. Usually this will resolve the problem and the fermentation will finish.
Maybe we can all learn something from the yeast: When you get stuck, take a bath, give yourself a fresh start, then slowly ease back into it and you’ll solve the problem in no time!