WHOLE-CLUSTER FERMENTATION & CARBONIC MACERATION

Here are my (Erik) study notes on Whole Cluster Fermentation and Carbonic Maceration.

WHOLE CLUSTER FERMENTATION

The stems consist of a rachis (the main stem), pedicels (connecting the berry to the rachis), and a peduncle (connecting the rachis to the vine). The stems remain green and photosynthetic until late in the season when lignan is deposited between cellulose walls, turning the stems brown and more brittle. Stems account for 3-7% of total bunch weight.

Process:

-        Historically, all wines were either direct pressed or fermented with the stems

-    Earliest technologies to destem were either by hand or using screens like the Chilean zaranda method

-    Destemming now is mostly done by machines.

-    Machine harvesters only harvest grapes, not stems

-        Destemming a small number of grapes into the tank first can prevent the development of volatile acidity and brettanomyces because alcoholic fermentation kicks off quicker

-        Stem inclusion has both a chemical and a physical impact on fermentation

-        Fermentation continues after pressing thanks to juice stuck inside intact berries

Factors:

-        Different flavours are extracted in an alcoholic solution (i.e. more is extracted post-fermentation)

-        Many producers are now advocating for the tasting of stems – sweet and tender should be used, bitter and fibrous shouldn’t

-        Temperature greatly affects flavour extraction – pre-fermentation cold-soak vs post-fermentation maceration

Outcomes:

-        Stems can add freshness in a hot vintage and softness in a cold one

-        Some winemakers claim stems can give a false sense of complexity and terroir

-        Ferments are generally cooler; this extends fermentation which may be a factor in complexity but can also make the wine susceptible to spoilage.

-        Wines pressed off whole cluster ferments tend to be cleaner thanks to the filtering effect of the stems – this means fewer rackings are required, and yields are higher at lower levels of pressure

-        Whole cluster ferments are harder to punch down, which means less extraction

-        Stems absorb colour

-        Potassium in the stems combines with tartaric acid to precipitate out, lowering the overall acidity of the wine

-    Stems in organic vineyards tend to have less potassium thanks to their fertilizer and compost regimes

-        Stressed fermentations tend to create more glycerol which improves mouth feel; the slow introduction of sugar by berries popping during cap management helps extend fermentation

-        Flavours can be cited as earthy, mulchy, herbal, cinnamon, tea

-        Mould on stems (powdery mildew or botrytis) seems to be even more noticeable

-        Stems have tannin, which can contribute to volume

carbonic maceration

Carbonic Maceration refers to a process in which intracellular fermentation occurs in intact grapes where malic acid is converted to ethanol via glycolytic enzymes. Invented by Michael Flanzy in 1934, it is now a popular technique used around the globe.

Process:

-        Traditionally, whole clusters of grapes are used, although there is some argument for gentle modern destemmers keeping berries intact enough to carry our carbonic maceration

-        The clusters are added to a tank which is then filled with CO2

-    Environment needs to be less than 5% oxygen and over 50% CO2

-    Typical air is 21% oxygen and less than 1% CO2

-    CO2 can be created naturally by crushing some of the berries and allowing for alcoholic fermentation or adding fermenting juice to the bottom of the vat

-    Typically, CO2 is pumped in from a compressed gas tank

-        In this environment the living grapes transition from respiratory to fermentative anaerobic metabolism

-    It is theorized that grapes developed this ability to stay alive in harsh conditions, making them more appealing to potential seed distributors

-        The enzyme Malic Acid Dehydrogenase makes ethanol, succinic acid, and aminobutyric acid

-    Catabolism of Malic Acid into ethanol without the production of lactic acid

-  Malic acid is converted to pyruvate

-  Pyruvate is decarboxylated to acetaldehyde

-  Acetaldehyde is reduced to ethanol

-        Temperatures of ~30º are recommended for a speedy fermentation

-        This process can take from 2-10 days depending on a wide variety of factors (temperature, variety, acidity, etc)

-        Once the grape reaches 0.5-2% ABV, the cell membrane is disrupted, causing death

-        Grapes will eventually need to be crushed to undergo yeast fermentation

-    This pressed juice tends to be particularly susceptible to bacterial spoilage because acids have dropped, and saccharomyces populations are still low

-    Typically only takes 2-7 days

-        If possible, malolactic conversion should be delayed until after alcoholic fermentation

Outcomes:

-        A small amount of alcohol is created (0.5-2%)

-        Malic acid is reduced by 15-75%, which equates to a pH increase of up to 0.6 units

-        Dry extract, fixed acidity, and residual sugars are lower in Carbonically Macerated wines

-        Phenolic compounds can be higher or lower depending on maceration times

-        Polyphenol and Polysaccharide ageing is similar between traditional AF and CM

-        Aromatics and polyphenols (anthocyanins, etc) are diffused from the skin into the pulp

-        There’s an argument for amplified varietal characteristics in certain cultivars

-        C6 Aldehydes responsible for herbaceous qualities are greatly reduced by CM

-        Creates Isoamyl Acetate: bubble gum, banana, pear, shoe polish

-        Volatile Acidity and Brettanomyces are hard to prevent

o    Oxygen between the stems

o    Struggling ferments due to low sugar availability making room for spoilage organisms

-        Greater production of glycerol which improves mouthfeel

-        Amino acids are liberated from grape solids which form flavour precursors

o    Cinnamate: strawberry/raspberry via the esterification of ethanol

o    Benzaldehyde: cherry/kirsch

o    Vinylbenzene: plastic

Anecdotes

-        Dujac claims stem use increases complexity and makes tannins silkier

-        Eric Texier has seen that the conversion factor is lower for whole cluster fermentation, which means lower alcohol levels controlling for sugar

-        Jules Chauvet believes the initially dominant aromatics will subside quickly, revealing more regional differences between wines

-        Claus Preisinger doesn’t destem in hot vintages because the stems are dried out and brittle, causing them to shatter which actually increases the surface area, making wines more stemmy when destemmed

-        Alex Craighead finds that oftentimes, more is less, meaning higher stem inclusion percentages can seem more cohesive

-        Franz Weninger finds the risk of VA really high but will still use 10-20% for Blaufrankisch. Any higher and he finds the wines too Glou Glou