Whole Cluster Fermentation
We use whole cluster fermentation for our Aulos brand because we believe it results in additional structure and spicy tannins from the stems. Our 2021 vintage was the first time we use whole cluster fermentation, we started the first vintage of Aulos with 35% of the fruit being whole clusters from Wadenswil.
For the 2022 vintage, we went 100% whole cluster with our estate 777 selection, and used a hint of carbonic maceration to produce a lighter fruitier style of wine. We didn’t use a sealed fermentation vessel and relied on the blanket of CO2 produced by the fermenting fruit to push the grapes into anaerobic activity. In carbonic maceration, fermentation is not caused entirely by yeast inoculation, but instead occurs intracellularly within the grape, from the inside out.
In an oxygen-free / anaerobic environment, the live berries begin to ferment from the inside. The grapes need a source of energy to maintain their cellular processes and organization. Under normal circumstances, they use oxygen from the atmosphere to break down sugar using aerobic respiration to produce CO2, water and energy. However, when atmospheric oxygen falls below 1%, grape metabolism to internal fermentation to break down sugars. In the absence of oxygen, grape cell metabolism converts sugar to ethanol through glycolysis followed by a final step that produces ethanol, a process much the same as yeast fermentation.
This reaction only proceeds until approximately 1.5-2% alcohol has been produced inside the grape, at which point the accumulated alcohol becomes toxic to the cell causing it to rupture. The by-products of auto-fermentation introduce interesting flavors and aromas into the resulting wine. Phenolic compounds are released from cellular compartments; anthocyanins and eventually tannins leach from skins into the pulp.
Increase in berry aroma and flavor - Modification of the metabolic pathway that usually leads to the production of amino acids instead leads to the production of volatile compounds such as ethyl cinnamate, benzaldehyde, ethyl decanoate, and many others. These compounds contribute to aromas of strawberry, raspberry, cherry and kirsch that distinguish whole cluster fermented wines.
Decrease in vegetal aroma and flavor - Lower oxygen limits the oxidation of fatty acids that can lead to production of C6 compounds hexyl acetate and hexanol, known for vegetal, tomato-leaf flavors and aromas.
Development of tertiary aroma and flavors - Intracellular enzymes break down proteins, releasing amino acids that can later serve as nutrients for yeast and bacteria as well as and precursors to other flavors and aromas.
At the same time, polyphenols, known to most as tannins and anthocyanins, make their way from the grapes’ skin to the pulp, which turns the white flesh to a pink color. Once the alcohol reaches 2%, the berries burst, releasing their juice naturally. Fermentation finishes via yeast at that point as yeast grows naturally on the skins of grapes (if a natural fermentation is desired) we inoculate the juice with yeast.
The weight of the fruit in our fermentation vessel was sufficient to press juice from the clusters at the bottom and to get a traditional yeast fermentation going. A cap forms due to fermentation emitting C02 which causes a thick layer of skins, stems and seeds to rise to the surface of the vessel. We pumped juice from the bottom of the fermentation vessel over the cap to keep the cap moist and also to extract additional color from skins and stems, and additional flavor and aromas from the grape solids.
There are three fractions of wine at play in this process. The upper most grapes in the sealed fermentation container undergo auto-fermentation at the top of the vessel in the CO2 enriched environment. Grapes undergo auto-fermentation to a lesser degree in the middle of the vessel surrounded by yeast fermenting juice. And juice at the bottom of the vessel that is undergoing a traditional yeast based fermentation. The dimensions of the fermentation vessel vary the interplay and contribution to the resulting wine of these fractions. Initially there isn’t much juice at the bottom of the fermentation vessel but additional sugar and nutrients are added as auto-fermenting grapes rupture causing a slow and steady fermentation process. After 5-8 days auto-fermentation is complete and the remaining pulp is pressed.
The stems in whole cluster fermentation add potassium, which can elevate pH as potassium binds with tartaric acid to form insoluble bitartrate. Stems also contain methoxypyrazine (over 50% of the pyrazine in grape clusters are found in the stems) that can lead to interesting spicy vegetal/herbal notes (Oregano, Juniper, Cardamom, Nutmeg, Black Tea, Rosewood, etc). Stem tannins soften over time, in addition to adding interesting spiciness to the flavor and aroma, they also produce a silkier mouth feel to the wine while improving ageability.
The controlled carbonic maceration technique was invented in the Beaujolais region of France, just south of Burgundy, where the light to medium bodied Gamay grapes are used to make Beaujolais. The reputation of those wines was elevated thanks to carbonic maceration, particularly Beaujolais Nouveau, an early-drinking wine released just weeks after fermentation is complete.
This process results in a low tannin, fruit driven wine style that’s lighter in color with low levels of acidity and fruity aromatics. Fresh, fruity, and light on tannins is the wine style we are after in Aulos - a wine intended to drink young, we consider it our summer Pinot. What we are trying to capture in Aulos is the terroir; a wine that is fresh as the memory of harvest and raw as the experience of the year, unpolished by time, purity in the reflection of the moment.