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Best Practices for Juice Clarification via Settling

Last updated: 6/2021

Applies to: Winemakers looking for product and process recommendations for clarifying juice via settling.

WHY CLARIFY?

Juice clarification is an important consideration in the production of white and rosé wines. Freshly pressed must can contain up to 20% solids consisting of small particles of cellulose, hemicellulose, pectin, mineral salts, lipids, and proteins. Based on variety and pressing method, the quality and quantity of grape solids in a juice can vary widely; however, it is beneficial to reduce solids content prior to fermentation for all white and rosé juices to 60-250 NTU’s or 1-2% solids. NTU's, or Nephelometer Turbidity Units, are a unit returned by a Nephelometer and help quantify the "cloudiness" of a juice or wine. This instrument is not only helpful when clarifying juice, but at many points throughout the winemaking process including heat stability and filtration.

Benefits of solids reduction (clarification) include:

  • Fresher, fruitier wines
  • Reduced sulfur-like off odors
  • Better color as enzymes responsible for oxidation have been removed
  • Reduction in vineyard residues (e.g., SO2)
  • Reduction in acetic acid producing native microflora
  • Compact deposit which minimizes juice loss
  • Increased fermentation kinetics

Clarification can be achieved via static settling, flotation, centrifugation, or filtration. To learn more about juice clarification via filtration, read our piece "Best Practices: Juice Clarification via Flotation."

What is Static Settling?

The most used clarification method is static settling. This involves chilling fresh pressed white and rosé juices, adding settling/clarification aids, and waiting for solids to fall out of solution and compact at the bottom of the tank. Clarified juice can then be racked off the top of the solids. There are 3 phases to static settling:

  • De-pectinization. This can be achieved via enzyme addition.
  • Flocculation of particles. This can be achieved via settling/clarification agent addition.
  • Sedimentation. This is achieved over time.

See below for key considerations and product recommendations at each stage.

De-pectinization:

The de-pectinization step can be achieved via an enzyme addition directly into the press pan as the juice is transferred to the settling tank. When grapes are pressed, pectin is released into the must and the amount can vary widely based on variety and vintage conditions; however, if not broken down, pectin can prevent settling.

FLOCCULATION OF PARTICLES:

The flocculation of particles can be achieved via the addition of clarification aids. Clarification aids bind with suspended insoluble solids creating larger molecules called floccules, which fall out of solution more quickly than the unbound solids. In addition to increasing sedimentation rate, fining agents added in the juice phase can also remove oxidizable phenolic compounds, harsh/bitter compounds, undesired color pigments, or aroma compounds from compromised grapes or color pigments.

The following clarification aids can either be added directly to the press pan or to the tank:

To determine the most appropriate fining agent and dosage bench trials should be conducted. These bench trials should be representative of the juice conditions, especially temperature.

NOTE: Bentonite-based fining agents like GRANUBENT ® PORE-TEC or BENTOLACT S should be used with care during settling - adding them too quickly after an enzyme addition can reduce the efficacy of or inactivate the enzyme. Enzymes like RAPIDASE can be used in this case; they work quickly (4-6 hours) in cold conditions.

SEDIMENTATION:

Sedimentation- Although particle size and viscosity are important factors in static settling, the time for the floccules to settle to the bottom of the tank is dependent upon numerous other factors including gravity and distance. However, a normal juice of low pectin and low protein content can clarify in as little as 24 hours.

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