Harvest 2008, Merlot Fermentation.


It has been a little over one month since we first harvested Sauvignon Blanc on a scorching summer day. In the weeks that followed, the seemingly endless heat wave that hit Northern California from middle August to early September subsided. Since then, we have harvested about 50% of our red wine grapes; starting with Merlot on September 4.
A frightening thing happened when we started harvesting Merlot . When the small, tight, thick-skinned, purple pearls dropped from the destemmer our must pump would not carry the grapes to tank. So, we had to carry 12 tons of Merlot in five gallon buckets (about 40 lbs) up the cat walk and hand dump the grapes into tank. It was fun the first few flights, but when the day waned on, the only thought I had was, if this is a sign of things to come, this is going to be one physically demanding harvest. Thankfully, when we started picking Cabernet last week, the grapes were a bit juicier and the pump was working again.

There was a bright spot in Merlot's ominous start. Due to the extreme weather conditions in Napa this year, grape cluster weights have been abnormally light and berry sizes intensely small. As we tracked the vineyard's development throughout the growing season, we anticipated these yields. But the old adage is, if you think you will have a big crop, it will be bigger, if you think you have a small crop, it will be smaller. In the Merlot section of our vineyard, where we typically farm four tons to the acre, we harvested less than two tons an acre. We consoled ourselves with the inherent quality that is expected in a small crop year. Small crops bring out the best in wine grapes - highly concentrated wines with firm structure and power that derive from low juice to skin ratios.

At the time of today's post, we'll be pressing off the Merlot and settling the free run before barreling down the young wine to finish fermentation in barrel. In my next post I will outline in pictures the sorting process - the process that gets the grapes to the tank for fermentation. But today, I will talk a little about fermentation management.

With the heavy lifting behind us, it was time to let the Merlot grapes soak for a few days on their skins. Many philosophies and studies have been done about pre-fermentation maceration, i.e. the cold soak. Some winemakers and some grape varieties react differently during this period, but the general consensus is that the optimal cold soak (whether three days or thirty days depending on the winemaker's style) will enhance color extraction and stability during the pending fermentation process. You can control the duration of the soak with temperature, keeping it cold, to inhibit native fermentation from taking place.

Fermentation occurs when the yeasts present in the fruit come in contact with the sweet juice releasing from the berries in a warm environment. Stick twelve tons of grapes in a closed vessel and I promise it will get warm and sticky pretty quickly. We chose to soak for four days before jump-starting fermentation by inoculating with an un-intrusive yeast strain that allows the fruit to develop its own character during the fermentation process.

After inoculating, there are a couple of different fermentation management processes. In order to facilitate this process we choose to aerate the juice by using a method called pumping-over, a process the French call remontages. With the use of an impellor pump we drain the juice from the tank and sprinkle it over the top of the tank back onto the grapes. As the fermentation progresses we choose to aerate the juice to supply oxygen to the yeast to keep them active. On the front end it is a savage process and on the back end it is soft and subtle. We drain the juice from the tank and it pounds through a screen, a sieve, before we pump the accumulating and aerated juice back onto the skins.

On a daily basis, it is our goal is to have all the available juice come in contact with the grape skins to develop extraction. Think of macerating a tea bag in boiling water. If left to its own device, the tea bag will float on top of the water and produce little flavor. If gently bobbed in the water by the drinker's hand, color and flavor will fill your cup gradually. This is an easy way to think about why we have to assist the grape juice to come in contact with the skins during this process. As the wine ferments, changing sugars to alcohol, its offshoot is carbon dioxide (CO2) that lifts the skins to the top of the tank. Think of the tiny bubbles in your carbonated water rising to the top of your glass. Add a lemon slice to your Pellegrino and it floats. At this point, it is said the “cap” (the grape skins) has risen, and if you do not continue your pump-overs (or punch-downs, the process of physically submerging the skins in the juice) you will not fully extract the wine's flavors and structure from the grape skins.

During this chemical process, the grape must heats up naturally, the tough berries soften and begin to release their sugary juice and the yeast strains feed on the sugar converting them to alcohol. We believe that the grape juice is “dry” (containing little or no sugar) at one gram per liter (of liquid). That's 1/1000 th parts sugar per liter, 33 ounces of liquid. Or a scant amount of sugar in your (750 mL, 24 ounce) bottle of wine. When a wine goes “dry” it is not finished. Secondary fermentation (for red wine) needs to be completed. Secondary, or malolactic, fermentation changes tart malic acid into softer lactic acid. When this process is completed, it is necessary to remove the wine from the sediments (lees) that are formed during the process so the young wine can begin its maturation or development into the wines we drink on a daily basis. Or at least I hope you are drinking on a daily basis. In future, post-harvest, posts I will track the development of our Merlot so you can follow it into its final, bottled package, our Firebelle

Dan Petroski is Assistant Winemaker at Larkmead Vineyards in Napa Valley. Dan has an MBA from New York University and worked as an Ad Exec in New York for several years, before switching it up and trading his suit for a move out west.


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