YAN testing

Yeast Assimilable Nitrogen (YAN) is the sum of Free Amino Nitrogen (FAN) plus ammonium. These are the sources of nitrogen that yeast cells can use for the purpose of growth and metabolism, and adequate nitrogen is necessary to ensure a healthy fermentation. Too little YAN can result in problems such as stuck fermentation or the over-production of hydrogen sulfide, while too much YAN can result in excessive ester production and poor flavor stability.

The most economical way we can measure YAN is by using a few reagents and a pH meter. This simple and rapid testing method is called a formol titration, and dates back to 1907. It begins by titrating a sample to pH 8.2 with sodium hydroxide (NaOH), and from this you can find the titratable acidity value if desired. Then formaldehyde is added, which reacts with free amino groups of alpha-amino acids causing the amino acid to lose a proton (lowering the sample pH) which can then be titrated, along with free ammonia. The sample is then titrated back to 8.2 as before. The YAN value is calculated from the amount of NaOH used in the second titration. This estimates YAN to within approximately 20 mg/L nitrogen. YAN measurements, ideally, should be performed right before pitching yeast in order to avoid over-estimation due to normal protein losses that occur during processing.

The formol titration over-estimates nitrogen from proline (which yeast cannot use) and under-estimates nitrogen from arginine. These two errors are, at least, partially offsetting. FYI only about 17% of the available proline is titrated.

Caution: The formaldehyde and methanol reagent is flammable, toxic, and carcinogenic. Keep away from sparks and open flame. Do not inhale fumes or ingest any solutions containing it. Do not pipet by mouth! Perform all steps with formaldehyde in a well-ventilated environment. Wear laboratory gloves and safety glasses at all times when handling formaldehyde. If contact with skin or clothes occurs, flush with plenty of water and apply a solution of sulfite powder (1 tsp/50 mL water).
Disclaimer: Brewing Forward editors are not liable for any damage(s) caused by the use of these materials or procedures. See our general disclaimer.

Testing materials

• pH meter (0.02 pH resolution required) plus calibration solutions
• 37% Formaldehyde/15% methanol
• 0.1 N or 0.133 N sodium hydroxide (NaOH)
• Sulfite powder
• Distilled water
• Plastic transfer pipette
• 15 mL conical tube
• 10 mL syringes
• Wash bottle for rinsing

Products

NaOH	0.1 N NaOH from Amazon 0.1 N NaOH from MoreBeer 0.133 N NaOH from MoreBeer
Formaldehyde	Vinmetrica YAN kit on MoreBeer Includes: formaldehyde, sulfite powder, 3 plastic transfer pipettes, and a 15mL conical tube. Formaldehyde from Amazon Formaldehyde from Presque Isle Wine Cellars

Note that phenolphthalein can be used as an indicator in place of a pH meter, but it does not provide the same precision and accuracy.

Testing procedure

1. Calibrate the pH meter. (See pH testing)
2. Adjust pH of the formaldehyde:
   • Add 5–10 mL formaldehyde into the 15 mL conical tube.
   • Add NaOH to the formaldehyde one drop at a time, mixing well, until the pH is between 7.5 and 8.5. Be sure to rinse the pH electrode before proceeding to the following steps.
3. To a small beaker or similar vessel, add 10.0 mL of the clear sample to be tested.
4. Add 10 mL water to the beaker.
5. Fill a 10mL syringe with NaOH and slowly add it to the beaker while mixing until you reach pH 8.2–8.3. If the end point goes above pH 8.5, repeat the sample preparation steps. The TA value can now be calculated if desired, but is not needed to complete the test.
6. Add 2.5 mL of the pH-adjusted formaldehyde to the beaker and mix well for about 1 minute.
7. The pH of the sample will drop. Titrate back to pH 8.2–8.3 with the NaOH (be sure to note starting and ending volumes on your syringe).
8. Calculation:
   • For 0.1 N NaOH: YAN, mg/L = [mL of NaOH added in the last step] × 0.1 × 1400
   • For 0.133 N NaOH: YAN, mg/L = [mL of NaOH added in the last step] × 0.133 × 1400

Clean-up:

1. To neutralize any residue of formaldehyde, add ¼ teaspoon (about 1.5 g) of sulfite powder for every 1 mL formaldehyde used. Mix well and allow to stand for at least 1 hour. Dispose in accordance with local regulations with plenty of water.
2. Turn off the pH meter. Rinse and store the electrode properly.
3. Rinse all plasticware with clean water.
4. Reagents should be stored at room temperature out of direct sunlight and away from children.

How much YAN is recommened for wine

Many yeast and nutrient manufacturers follow a study by the UC Davis Department of Viticulture and Enology relating optimal nitrogen levels (in milligrams of nitrogen per liter, mg N/L) to wine’s brix level at harvest:

• 21°Bx = 200 mg/L N
• 23°Bx = 250 mg/L N
• 25°Bx = 300 mg/L N
• 27°Bx = 350 mg/L N

Typical values for YAN are 50 to 500 mg/L in must.