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Sweet Wine Production

Ice Wine and Late Harvest Production

Technical guide to producing naturally frozen ice wine and late harvest sweet wines; concentration methods, harvest timing, fermentation challenges, and regulatory requirements.

6 min read
Eno Codex Editorial

Ice Wine and Late Harvest Production

Problem Definition

Ice wine (Eiswein) and late harvest wines represent the pinnacle of concentration-based sweet winemaking, requiring precise timing, specific climatic conditions, and specialized vinification techniques. The challenge lies in achieving sufficient concentration naturally (without artificial means) while preserving varietal character and acidity. Understanding the regulatory frameworks, concentration methods, and fermentation challenges enables production of these premium sweet wines.

Technical Context

Concentration Mechanisms

Natural Freezing (Ice Wine):

  • Grapes freeze on vine at ≤-7°C to -8°C
  • Water freezes; sugars remain liquid
  • Pressing extracts concentrated juice
  • Dramatic concentration achieved

Desiccation/Dehydration (Late Harvest):

  • Extended hang time on vine
  • Water evaporation concentrates sugars
  • Botrytis may or may not be involved
  • Gradual concentration

Sugar Concentration Levels

Wine TypeMinimum Sugar (°Oechsle)Typical °Brix
Spätlese76-8518-20
Auslese85-10020-24
Beerenauslese (BA)110-12826-30
Trockenbeerenauslese (TBA)150-180+35-45+
Eiswein110-12826-30

German Prädikat System

Classification Hierarchy:

  1. Kabinett: Lightest Prädikat; no concentration
  2. Spätlese: “Late harvest”; riper grapes
  3. Auslese: Selected bunches; botrytis possible
  4. Beerenauslese (BA): Selected berries; botrytis required
  5. Trockenbeerenauslese (TBA): Dried berries; botrytis essential
  6. Eiswein: Frozen grapes; no botrytis required

Options and Interventions

Ice Wine Production (Eiswein)

Harvest Requirements:

  • Temperature: ≤-7°C sustained (Germany: -7°C; Canada: -8°C)
  • Grapes must freeze on vine
  • Harvest typically November-January
  • Night harvest (temperatures coldest)
  • Must remain frozen during pressing

Pressing Protocol:

  1. Harvest frozen grapes
  2. Immediate pressing (outdoor or unheated)
  3. Very slow pressing (frozen berries hard)
  4. Initial juice: Highest concentration
  5. Later juice: More dilute (ice melting)

Typical Parameters:

  • Yield: 5-15% of normal (most water frozen)
  • Must weight: 26-40+ °Brix
  • Acidity: Very high (concentrated)
  • pH: Low (2.9-3.3)

Varieties:

  • Riesling: Classic German; high acid retention
  • Vidal (Vidal Blanc): Canadian standard; cold-hardy hybrid
  • Grüner Veltliner: Austrian
  • Cabernet Franc: Canadian red ice wine

Late Harvest Production

Spätlese Level:

  • Extended hang time (2-4 weeks beyond normal)
  • Higher sugar accumulation
  • May or may not be sweet (fermented dry = “trocken”)

Auslese Level:

  • Selective harvest of riper bunches
  • Botrytis possible/common
  • Higher concentration

Beerenauslese/Trockenbeerenauslese:

Fermentation Challenges

High Sugar Fermentation:

  • 26-40+ °Brix creates extreme osmotic stress
  • Yeast selection critical (high sugar tolerance)
  • Very slow fermentation (weeks to months)
  • Cold fermentation (12-16°C)
  • Stuck fermentation risk high

Yeast Selection:

  • High sugar/alcohol tolerance essential
  • Examples: EC1118, VIN 13
  • Nutrient supplementation critical
  • Acclimation protocols

Natural Fermentation Arrest:

  • High sugar wines often self-arrest
  • Yeast dies from alcohol + osmotic stress
  • 9-12% ABV typical final
  • Residual sugar: 150-300+ g/L

Trade-offs and Risks

Production Risks

Weather Dependence:

  • Requires sustained freeze (ice wine)
  • Climate change reducing reliable conditions
  • Bird/animal damage during wait
  • Rot (not noble rot) risk

Economic Risk:

  • Very low yields
  • High labor (selective harvest)
  • Weather-dependent production
  • Premium pricing required

Quality Risks

Over-Concentration:

  • Can lose varietal character
  • Excessive sweetness
  • May become cloying

Under-Concentration:

  • Insufficient freeze/concentration
  • Dilute character
  • Does not meet regulatory minimum

Fermentation Risks

Stuck Fermentation:

  • Very common with high sugar
  • Volatile acidity risk during stuck
  • May require restarting

Practical Implications

Regional Production

Germany (Mosel, Rheingau):

  • Eiswein: Riesling dominant
  • TBA: Requires botrytis
  • Climate change: Production increasingly difficult
  • Authentic, historic tradition

Canada (Niagara, Okanagan):

  • World’s largest ice wine producer
  • VQA regulations: -8°C minimum
  • Vidal (hybrid) and Riesling
  • Reliable cold temperatures

Austria (Burgenland):

Tokaj (Hungary):

  • Aszú: Different system (puttonyos)
  • Botrytis-based concentration
  • Furmint variety

Quality Assessment

Must Parameters:

  • Sugar: Meet Prädikat/regulatory minimum
  • Acidity: Balance essential (>7 g/L ideal)
  • Health: Clean, no gray rot

Wine Parameters:

  • Residual sugar: 100-300+ g/L
  • Alcohol: 7-12% ABV typical
  • Acidity: High (balances sugar)
  • Color: Golden to amber (white); deep (red)

Aging Potential

Properly Made Ice Wine/TBA:

  • 10-50+ years aging potential
  • High sugar acts as preservative
  • High acid maintains freshness
  • Develops honeyed, complex character

References

  • VDP (2024). “Prädikatswein Classification.” https://www.vdp.de

  • Canadian Vintners Association (2024). “VQA Ice Wine Standards.” Link

  • Ribéreau-Gayon, P., et al. (2006). “Handbook of Enology, Volume 2.” Wiley. Publisher Link

  • German Wine Institute (2024). “Prädikat wine regulations.” https://www.germanwines.de

Last Updated: January 6, 2026