Nitrogen

Question 1

When is the best time to add nitrogen?

Answer 1

✅ The moment of addition impacts cell growth.
✅ Early addition (beginning to mid-fermentation): Increases max cell population but does not affect AF duration.
✅ Late addition (mid to late fermentation): Little impact on growth but prolongs AF duration.

Question 2

What are YAN requirements during fermentation?

Answer 2

✔️ Mid-fermentation YAN needs vary by yeast strain.
✔️ All yeast strains require similar YAN at the beginning of fermentation.

Question 3

What forms of nitrogen can be added to must?

Answer 3

✅ Only inorganic nitrogen (ammonia-based):

• DAP (Diammonium phosphate) or DAS
• Mix of N salt + thiamine
  📌 Advantages:
  ✔️ Quick assimilation
  ✔️ Accelerates AF speed
  ✔️ Cheap (~€4/kg in France)

📌 Downsides:
❌ Exothermic reaction → Temperature increase
❌ Too much DAP → pH drop

💡 Alternative: Yeast-derived products (contain 5-10% organic nitrogen, but 8x more expensive than DAP/DAS).

Question 4

What is the necessary initial YAN concentration?

Answer 4

✅ 140-150 mg N/L → Ensures enough yeast population and avoids sluggish/stuck fermentation.

📌 If sugar <230 g/L → No nitrogen addition needed.
📌 If sugar >230 g/L → Supplement with ammonia salts + thiamine up to 200-220 mg N/L at mid-fermentation.

Question 5

YAN Distribution in Grapes %

Answer 5

🍇 20% Skins
🍇 60% Pulp
🍇 20% Seeds
📌 Maceration reduces YAN levels since skins & seeds are removed.

Question 6

Forms of Nitrogen in Must

Answer 6

✔️ 1/3 Ammonium (NH4⁺)
✔️ 2/3 Amino Acids

📌 Proline is dominant but not included in YAN!

Question 7

YAN’s Role in Fermentation

Answer 7

✅ Essential for yeast protein synthesis → Affects cell growth, AF kinetics, and aroma production.
✅ Influences permease synthesis (carrier proteins for sugar transport).

📌 Low YAN →
❌ Low max cell population → Slower AF rate → Longer fermentation
❌ Low sugar transport → Risk of stuck/sluggish fermentation

Question 8

How does YAN affect aroma production?

Answer 8

✔️ Higher alcohols (can be negative in excess):

Herbaceous, fusel-like
✔️ Ester production (fruity aromas):

Ethyl acetate ↑ with YAN (can be negative)
Acetate esters
Fatty acid esters
Branched-chain esters
✔️ Thiols (Varietal aromas):

YAN increases non-odorous precursors → More transporters → Higher aroma potential
More DAP → Less 3MH production (thiol aroma impact)

Question 9

Acetic Acid Production & Nitrogen

Answer 9

📌 Acetate (volatile acidity) comes from stressed yeast cells.
📌 Too much or too little nitrogen → More acetic acid production.

Question 10

Sulfur Compounds & Nitrogen Deficiency

Answer 10

📌 Low nitrogen → H₂S (rotten egg smell) instead of proper methionine/cysteine synthesis.

Question 11

What is the nitrogen deficiency threshold?

Answer 11

✅ If must contains <140-150 mg N/L → Supplement with 150-200 mg N/L.
✅ Nitrogen uptake happens fast (~2-3 days), so careful timing of addition is crucial.

Question 12

Can you add nitrogen in parts?

Answer 12

✔️ Yes! If density drops, you can supplement later.
✔️ But late additions can impact AF duration.
✔️ Must aeration is crucial!

Question 13

How does NH4+ addition affect fermentation?

Answer 13

✅ NH4+ (≤200 mg/L at T=0) stimulates yeast growth
✅ Provides NADH, which reduces acetate production.

Question 14

Stuck Fermentation & Sugar Preferences

Answer 14

📌 Stuck fermentations → High fructose levels (S. cerevisiae prefers glucose).
📌 In Sauternes, high residual sugar (110 g/L) → High glucose/fructose ratio.

Question 15

If a wine smells like sulfur (rotten egg), what would you say regarding nitrogen levels?

Answer 15

There was probably a deficiency in YAN.

Question 16

Adding too much or too little nitrogen can cause stress, what is the by-product produced from this?

Answer 16

Acetate, vinegar.