Clarifying White Wine Juice Pre-Fermentation.
White wine making has a fascinating step called juice clarification that can get overlooked in the fermentation flowchart. Falling in between pressing and fermentation, must, or juice, clarification improves a white wine’s overall quality used to increase fruit character and varietal distinctiveness.
What Is Juice Clarification?
Juice clarification aims to reduce solids in the white grape juice that can cause issues for the winemaker later on during fermentation. Clarification happens right after the grapes are pressed and before the winemaker adds yeast to the juice.
The juice gets moved to a holding tank and solids suspended in the juice settle out by gravity. Small tanks are more efficient for settling than large tanks because there’s less volume. Imagine a small snow globe vs. a large snow globe; the snow settles faster in the smaller version.
The pressed grape juice settles for 12-72 hours, then gets transferred to a fermentation vessel through a process called racking.
The unwanted spoilage molecules and larger solids get left behind.
The winemaker may choose to add enzymes to speed up the wine clarification process.
One example is pectinase, which breaks down pectin, a plant carbohydrate that binds cell walls together.
Pectinase needs 2-4 hours to work. Another example is settling enzymes that help with juice clarification. White wines treated with settling enzymes express better aromas and result in cleaner juice overall.
Settling enzymes will increase the amount of solids, or gunk, that gathers on the bottom of the vat, decreasing overall juice volume.
Helpful Tip: Interested in all-things wine science? Here’s the basics of how fermentation works.
What Exactly Does Clarification Remove from White Wine Juice?
Clarification removes unwanted things that are common on skins and/or in pulp, to include oxidative enzymes that can cause browning (e.g., polyphenol oxidase), mold and other spoilage organisms, and possibly an enzyme that can reduce esters during yeast fermentation (reducing aromatic compounds).
The goal isn’t to reduce all solids in the grape juice. The winemaker wants to keep ~0.5%-1.0% of the solids; these molecules provide nutrients to the yeast during fermentation.
Without them, the wine might become ‘stuck’ because of insufficient nutrients.
Helpful Tip: Here’s how winemakers decide what wine yeast to use. It’s a little bit like picking out vegetable seeds for your summer garden.
Does the Juice Just Sit There?
No, not exactly. During pre-fermentation grape juice clarification, the winemaker does a couple of things. First, she adds SO2 to the grape must. This inhibits any indigenous yeast from getting a foothold.
Second, she turns on the cooling jackets to chill the juice – also a way to delay the onset of fermentation. Third, she tests the juice for sugar, acid, pH, and nitrogen.
Helpful Tip: Check out the many different types of vessels winemakers can use to ferment their wine.
Speeding Up Pre-Fermentation Clarification: Improving Efficiency
As you might imagine, this process can be a bottleneck for wineries. Very large wineries that process huge volumes of wine might invest in a centrifuge to clarify juice and speed up the process.
The juice gets spun in a chamber and the solids are forced outward, away from the center.
Using a centrifuge can reduce production costs, increase volume, and decrease time to market. This adds an element of efficiency.
The winery doesn’t need to add SO2, spend money on chilling tanks, or time transferring the juice.
The centrifuge forcefully compacts the solids, improving overall yield.
Additionally, centrifuges are fast. They can remove solids immediately after pressing, allowing the winemaker to start the fermentation process immediately.
Centrifugation of Wine Juice.
Here’s a great video that explains how a large Italian winery is using a centrifuge in bulk wine production.
Thirsty for More?
Check out this post on how pricing for a bottle of wine works – it’s a little in-depth, but may be the right level of wine-nerd for you.
And here’s a post that goes over how a winegrower decides what grapes to plant where. Sometimes it’s economics, sometimes it’s science, sometimes it’s something else completely.