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VIDEO
Nitrogen analysis with YAN kit
MATERIAL AND REAGENTS
pH-METER HANNA EDGE
RSLAB MAGNETIC AGITATOR
GAB BURETTE SUPPORT NUT
BURETTE CLAMP
BEAKER 100ml L/F
BEAKER 50ml L/F
GRADUATED CYLINDER 25ml
PIPETTE OF 25ml 2 CAPACITIES CLASS "A"
25ml BURETTE PTFE KEY
NFA GAB PACK
CHEMICAL CONCEPTS
The growth and development of yeasts during the fermentation of a must requires the contribution of nutrients. These nutrients will be above all those that provide carbon (sugars) and nitrogen (ammonium, amione acids) among others.
Nitrogen can be found in mineral form in must and wine as ammonium cation NH4 + and as organic nitrogen in the form of free amino acids. Yeasts can quickly assimilate and use both.
During the harvest the determination of the NFA in the musts that have to be fermented is important to know if it is necessary to carry out a nitrogen nutrition (ammonium phosphate or organic nitrogen). These nitrogenous forms can be determined by adding an excess of formaldehyde that blocks the NH4 + group and in the amino acids, the amino groups, leaving the carboxyl groups, which reduces the pH in proportion to the amount of these nitrogenous compounds.
OPERATIVE TECHNIQUE
1- In a 100ml beaker pour an approximate volume of 50ml of formaldehyde and, with the help of a pH meter, neutralize it very slowly to approximately pH 6 using the 50ml dropper and continue until pH 8.00 with the burette, filled with titration liquid. Reserve the reagent for analysis and save the remainder for subsequent repetitions.
2- In a 50ml beaker, pour 25ml of wine or must measured with a double-flush pipette and add 2-3 drops of 33% hydrogen peroxide (10ml dropper).
3- With the 50ml dropper, slowly neutralize the wine or must to approximately pH 6 and continue to pH 8.00 with the burette containing titration liquid.
4- Once the wine or must has been neutralized, add, measured with a measuring cylinder, 10ml of the formaldehyde previously prepared. The pH of the mixture will drop slightly, wait approximately 1 min or until the pH meter reading stabilizes.
5- Make up the burette with titration liquid and neutralize the mixture again at pH 8.00 and multiply the milliliters used by 56, thus obtaining milligrams per liter of Easily Assimilable Nitrogen (NFA):
ml spent in burette x 56 = mg / l NFA
OBSERVATIONS
Perform neutralizations slowly
33% hydrogen peroxide is used to eliminate the SO2 present, preventing it from interfering with the result. Handle with care.
Formaldehyde is relatively unstable and polymerizes, lowering the pH, so only the amount necessary for the day's analysis should be neutralized at pH 8.00 and stored at more than 20ºC. The presence of turbidity or precipitate in the reagent does not affect the analysis. Avoid inhalation.
The content of Easily Assimilable Nitrogen (NFA) in musts is highly variable, since it depends on many factors such as: the soil, the climate, the nutrition of the vineyard, the variety, etc. Must with values between 200
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