Récolte de raisins. Vendages

In the last article, we looked at the  importance of maturity monitoring.  We say that oenological maturity, phenolic maturity and technological maturity are not necessarily linked.  If maturity monitoring is important, must analyzes are critical.  In fact must analyzes are the very foundation on which the winemaking strategy will be based.

What is must analysis?

Must analysis be performed right after grapes are pressed and before yeast is added. Parameters measured are: Brix, Fermentable Sugars (glucose-fructose), Density, pH, Titrable Acidity, Tartaric Acid, L-Malic Acid, Potassium, Total Nitrogen (Ammonia and Amino Nitrogen).

Why perform must analysis?

Must analysis, like maturity monitoring, informs the winemaker on the quantity of fermentable sugars present as well as on levels of tartaric and L-malic acids.  These values are important because knowing the amount of sugar in the must will indicate whether or not the winemaker needs to chaptalize.  Acids levels will inform the winemaker whether of not to perform a deacidification.  Unfortunately, in our northern climate, grape maturity is sometimes hindered by an early frost.  The winemaker and the oenologist have to decide how to manage unripe grapes and will rely on the measured amounts of tartaric acid, L-malic acid and potassium to design, if needed, a deacidification protocol.  These types of interventions need to be precise to avoid denaturing the wine and this is exactly what a professional laboratory can bring. However, the most important parameter to measure in musts is total nitrogen which includes ammonia and amino nitrogen.  Potassium and nitrogen are not usually measured in maturity monitoring analyzes due to time and financial constraints.  Total nitrogen is essential to yeast fermentation.  A sluggish fermentation is often caused by low amounts of nitrogen.  If must analysis shows low amounts of total nitrogen, the winemaker can quickly intervene and add nutrients.  Low amounts of nitrogen in the must can lead to reduction because thiols produced by yeasts during fermentation and are usually complexed with nitrogen.  Low nitrogen will increase production of higher alcohols by yeasts which bring bitterness.  On the reverse side, a high amount of nitrogen will lead to higher ethyl acetate levels causing a nail polish aroma.  Less than 150 mg/L of total nitrogen is considered as a nitrogen deficiency.

To finish...

Samples sent to the lab for maturity monitoring and must analysis are analyzed as soon as they are received.  Results are usually transmitted with 4 hrs of receiving the samples.  The turnaround for these tests is very short and bring precious information to the winemaker and oenologist. Must can be frozen at this stage for shipping without the risk of tartaric precipitation because of the high sugar content.  They can also be shipped with an ice pack.  A minimal volume of 250 ml is needed for testing.

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