The harvest of 2023 in Germany is proving to be more challenging than expected due to early onset of rot. The fruit fly drosophila suzukii causes tiny bite damages, which in turn results in an increase in volatile acid risks. Several areas experience hailstorms, with partly catastrophic losses.
Given the choice between harvesting healthy grapes or waiting for higher ripeness, healthy grapes should be preferred under all circumstances. However, the inevitable batches with contaminations require specific microbiological protection.
For overall quality the early application of a moderate sulfurization, in combination with an adjustment of the pH level is often indispensable. Both measures ensure a control of microbiological risks and possible spoilage. Liquid options like Solution sulfureuse P15 and Boervin make the application practical, safe and easy.
Regarding the weather conditions in the current 2023 vintage, the influence of Botrytis could be anticipated. There is an early harvest, resulting in grapes that are not fully physiologically ripe. This leads to a nutrient deficiency, particularly in terms of yeast-available nitrogen and vitamin B1 (thiamine).
CarboTec GE facilitates the early and aroma-preserving adsorption of fermentation-inhibiting substances in grape must. This application is a preventive measure to remove pesticide residues and Botrytis notes.
Botrytis-affected grapes result in a decrease in yeast-available nitrogen in the must. To compensate for the nitrogen deficit, VitaDrive® ProArom is recommended as an addition to the yeast rehydration process. VitaDrive® ProArom contains all the amino acids preferred by yeast cells and has an increased antioxidant potential. The addition of VitaFerm® Ultra in the must (2x 20 g/100 L) promotes healthy yeast growth and prevents the formation of sulfur-like off-flavors.
Since Botrytis consumes the naturally occurring thiamine (vitamin B1) in grapes an addition of thiamine is essential to keep SO2-binding partners low. Thiamine can be added in its pure form as Vitamon® B Sticks or through combination products like Vitamon® Liquid, which can be added even during fermentation without foaming.
As well as nutrients a robust yeast strain for extreme conditions is needed. Oenoferm® X-treme is a very suitable option here.
The Challenge of Volatile Acidity
Contaminated grapes should not be brought into the cellar. A careful pre-selection is crucial for quality preservation. Unfortunately, complete avoidance is not always possible, as even a small number of grapes or even berries can lead to increased formation of volatile acidity in the must.
It is generally known that volatile acid is produced during fermentation by wild yeasts and bacteria, and occasionally even by added wine yeasts. Depending on the sugar content, individual wine yeasts can produce approximately 100-300 mg/L of acetic acid.
Far lesser known is the fact that, under certain conditions, yeasts can also metabolize volatile acid, reducing its content in the must. Typically, up to 200-300 mg/L of it can be metabolized during the early stages of fermentation, reducing the presence of acetic acid ethyl esters, which are responsible for the unpleasant solvent-like odors.
Additionally, contaminated grapes are not only rich in acetic acid but also deficient in essential amino acids and vitamins. They also contain fungal proteins that encourage yeast to produce acetic acid.
Bentonite and activated carbon treatments, as well as nutrient additions with complex nutrients, are therefore mandatory.
Factors affecting acetic acid formation by wine yeasts
General fermentation factors include low pH (<3.1), high pH (>4.0), amino acid and vitamin deficiencies, high temperatures during yeast multiplication in the must (25 – 30°C), and fermentation temperatures above 20°C, especially in red wine production. Botrytis glyco-proteins also play a role.
Factors promoting acetic acid reduction
Note: Removal of larger quantities of acetic acid through yeast respiration (macro-oxygenation) is possible but not highly recommended due to potential quality losses, especially when performed towards the end of alcoholic fermentation.
MaloStop F can effectively control bacteria, based on fumaric acid it is a safe way to prevent undesirable microbiological processes. Traditionally, SO2 has been the most effective method of choice, but MaloStop F offers a valuable complement and alternative for targeted elimination of lactic acid bacteria. Even a dosage of only 600 mg/L also lowers the pH by 0.1 – 0.2 points as a side effect, providing additional microbiological stability. It significantly enhances the effectiveness of SO2 treatments.
Hopefully your own harvest runs much more smoothly and offers you an exquisite quality potential to work with.
In case you have any questions or we can support you in any way, please do not hesitate to contact us: firstname.lastname@example.org We will be more than happy to get in touch with you!