Must Concentration Techniques

Problem Definition

Must concentration increases sugar content and flavor intensity in grape must, compensating for dilute vintages, underripe fruit, or achieving specific style goals. Techniques range from traditional (saignée, grape drying) to technological (reverse osmosis, vacuum evaporation). Each method has distinct quality implications, regulatory constraints, and cost considerations. Understanding when and how to concentrate—and when concentration is prohibited or inadvisable—is essential for quality-focused winemaking.

Technical Context

Concentration Objectives

Primary Goals:

Increase sugar/potential alcohol
Concentrate flavor compounds
Reduce water content
Compensate for dilute vintages

Secondary Effects:

Concentrates ALL solutes (including acids)
Affects tannin and color density
May alter phenolic balance
Can intensify both positive and negative compounds

Methods Classification

Traditional/Physical:

Saignée (juice bleeding)
Appassimento (grape drying)
Passerillage (on-vine drying)
Cryo-extraction (freezing)

Technological:

Reverse osmosis
Vacuum evaporation
Spinning cone
Cross-flow filtration

Options and Interventions

Saignée

Mechanism: Bleeding off portion of juice from red must, increasing skin:juice ratio.

Effect:

Concentrates remaining must
Increases color, tannin extraction
Byproduct: Rosé wine

Typical Volume: 10-20% of must bled

Limitations:

Modest concentration effect
Creates secondary wine stream
May over-extract if taken too far

Regulatory: Generally permitted worldwide.

Appassimento (Grape Drying)

Mechanism: Post-harvest drying of grapes to concentrate through water evaporation.

Key Example: Amarone della Valpolicella

Process:

Drying duration: 90-120 days
Weight loss: 30-40%
Environment: Controlled temperature/humidity (fruttaio)
Botrytis risk management

Effect:

Dramatic sugar concentration (26-32°Brix)
Flavor concentration
Unique dried fruit character
Enzymatic changes during drying

Limitations:

Labor/facility intensive
Spoilage risk
Limited to specific styles

Cryo-Extraction

Mechanism: Freezing grapes (naturally or artificially) and pressing; frozen water stays behind.

Key Examples:

Eiswein (natural freezing)
Artificial cryo-extraction

Process:

Natural: -7°C or below at harvest
Artificial: Cryogenic freezing post-harvest
Press frozen grapes immediately

Effect:

High sugar concentration (35°Brix+)
Concentrated acidity
Fresh fruit character preserved

Limitations:

Artificial version: Regulatory restrictions (varies)
Natural: Rare climate conditions required
High cost

Reverse Osmosis

Mechanism: Membrane separation; removes water through pressure differential.

Process:

Must/wine passed through membrane under pressure
Water (permeate) passes through
Concentrated retentate returned
Can target specific concentration level

Effect:

Precise concentration control
Water removal without heat
Preserves fresh character
Can also reduce alcohol post-fermentation

Limitations:

Equipment cost
Regulatory restrictions (some appellations)
Technical expertise required

Regulatory: Permitted in EU for must concentration; prohibited or restricted in some premium appellations.

Vacuum Evaporation

Mechanism: Low-pressure evaporation at reduced temperature.

Process:

Must heated under vacuum (~30°C)
Water evaporates at low temperature
Vapor removed and condensed

Effect:

Water removal
Some volatile loss possible
Faster than drying

Limitations:

Heat exposure (even if reduced)
Volatile compound loss
Equipment cost

Trade-offs and Risks

General Concentration Risks

Over-Concentration:

Unbalanced wines
Excessive alcohol potential
Loss of freshness
Intensified negative compounds

Quality Masking:

Cannot improve poor fruit quality
Concentrates flaws along with positives
Not a substitute for quality viticulture

Method-Specific Considerations

Method	Advantage	Disadvantage
Saignée	Simple, traditional	Modest effect
Appassimento	Unique character	Labor-intensive, risk
Cryo-extraction	Preserves freshness	Cost, availability
Reverse osmosis	Precise control	Equipment, regulations
Vacuum evaporation	Efficient	Volatile loss

Practical Implications

Appellation Regulations

Prohibited/Restricted:

Many premium European appellations restrict or prohibit technological concentration
Burgundy: Chaptalization preferred over concentration
Bordeaux: Concentration permitted with limits

Permitted:

Many New World regions
Some EU appellations (with restrictions)
Specific maximum concentration levels often defined

Vintage-Appropriate Use

Dilute Vintages:

Rain at harvest causes dilution
Concentration can restore balance
Must be used judiciously

Normal/Great Vintages:

Typically unnecessary
Risk of over-concentration
Natural concentration preferred

Style Applications

Amarone:

Appassimento essential to style
Not corrective—definitive

Premium Reds:

Saignée for enhancement
Subtle concentration for structure
Avoid obvious “concentrated” character

References

Ribéreau-Gayon, P., Glories, Y., Maujean, A., & Dubourdieu, D. (2006). “Handbook of Enology, Volume 2.” Wiley. Publisher Link
OIV (2023). “International Code of Oenological Practices.” https://www.oiv.int
EU Regulation 1308/2013. “Common Market Organisation for Wine.”
Jackson, R.S. (2014). “Wine Science: Principles and Applications.” Academic Press. Publisher Link

Last Updated: January 6, 2026