Pre Fermentation Analyses - Wine - Lecture Slides, Slides of Winemaking

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Pre-Fermentation Analyses

Overview

• Process overview
• Brix by Hydrometer
• Acidity
  • pH and TA (Completed during Maturity Assessment Module)
• Yeast Assimilable Nitrogen (YAN)
  • Ammonia(NH3)
  • alpha amino nitrogen (AAN)

Process Overview

1. Weigh fruit
2. Destem/Crush
3. Add SO
4. Take juice sample for analysis
5. Adjust acid and/or brix if needed

Pre-Fermentation Analysis

Why do we care about these?

• Brix – Sugar Concentration
  • By Refrac – Allows for check using same method used as with grape sampling
  • By Hydrometer – Initial sugar measurement
• pH – Number of protons in solution – Assess risk level
• TA – Titratible Acidity - used to make acid additions
• YAN – Yeast Assimilable Nitrogen (NH3 + AAN) – Measure Nitrogen for precise additions of DAP and Complex nutrients
• VA – Volatile Acidity – Indicator of spoilage
• Malic Acid – may allow for additional acid addition
• Microbiological Analysis – assess risk of microbial spoilage

Table 1: Typical YAN Levels Required

for Good Fermentations

Brix Average YANRequired YAN Range Required 21 225 200- 22 250 225- 23 275 250- 24 300 275- 25 325 300-

Hydrometry

• A hydrometer measures the specific gravity (or relative density) of liquids; that is, the ratio of the density of the liquid to the density of water.
• Sugar equates to over 90% of the soluable solids in in juice allowing for physical measurement that can be well correlated to sugar concentration.
• Measures % dissolved solids. THEY MUST BE DISSOLVED TO AFFECT LIQUID DENSITY.
• Measured in °Brix which is equal to grams per 100ml (g/100ml)
• Example 20 °Brix = 20% = 20 g/100mL = 200 g/L
• Alcohol is less dense than water and the the accuracy of the Brix measurement decreases as the fermentation progresses

Nitrogen

• A lack of Nitrogen may even lead to sluggish

or stuck fermentations

• You should be prepared to add Nitrogen at the

start of fermentation to prevent these problems.

• The total nitrogen in a fermentation is

measured by the sum of the alpha-amino nitrogen plus ammonia. (AAN + NH 3 = YAN)

Nitrogen

• If you want to avoid problems, you must be prepared to add nitrogen to your fermentations.
• Additions are often made either right before or after inoculation and once the fermentation reaches log phase.
• General Rule of Thumb – Do not add nitrogen below 12 brix to treat sulfides (use Copper Sulfate)

Alpha Amino Nitrogen by OPA

• AAN is the same as PAN or primary amino

nitrogen

• Often called an enzymatic analysis but is

actually a chemical analysis but the procedure is very similar

• Omits the measurement of proline which the

yeast do not use unlike with the Formol titration

OPA Reaction

Amino nitrogen + N-acetyl-L-cysteine + o-phthaldehyde isoindole derivative