Par Noémie Breton, œnologue
What is Lactic Spoilage?
Lactic spoilage is the result of uncontrolled growth of lactic bacteria during alcoholic fermentation. It is therefore, a microbial deviation.
Unlike malolactic fermentation, which is often used to soften wines by converting malic acid into lactic acid, the growth of lactic bacteria during alcoholic fermentation generates undesirable compounds and flavors.
This spoilage occurs when alcoholic fermentation accidentally stops or slows down. As a result, not all sugars are consumed by yeasts, thus creating an environment auspicious to the development of lactic bacteria. These bacteria multiply and break down residual sugars as well as the tartaric acid present in the wine.
Alcoholic fermentation is a key step in the world of oenology, transforming the must into wine thanks to the action of yeasts. However, other undesirable microorganisms can join in during this process, including lactic bacteria. While the role of these bacteria is well-known during malolactic fermentation, their presence during alcoholic fermentation may cause an organoleptic alterations known as lactic spoilage.
There are two types of bacteria:
1- Homofermentative bacteria which only produce lactic acid when degrading sugars,
2- Heterofermentative bacteria which produce ethanol, acetic acid and lactic acid when degrading sugars.
These compounds greatly affect the taste and mouthfeel of wine.
A wine under lactic spoilage shows symptoms such as:
- Increase in volatile acidity, sharpness upon tasting and aroma vinegar
- Aromas reminescent of rancid butter or yogourt
- A loss of freshness and balance upon tasting
What are the principal causes of Lactic Spoilage?
Many parameters come into play in regards of Lactic Spoilage:
During a sluggish fermentation, a must rich in sugars will provide an excellent energy source for bacteria. These conditions will drive bacteria proliferation even before the end of alcoholic fermentation resulting in spoilage.
Nitrogen or thiamine deficiency often lead to sluggish fermentations or even a stop in fermentation. Lactic bacteria, if present, will develop and take over the yeasts.
Low sulfites will provide an environment auspicious to bacteria.
High pH: pH higher than 3.5 will reduce SO2 efficiency in controlling bacteria.
High temperatures during fermentation or ageing
Bad cellar hygiene: Dirty tanks and hoses are contamination sources during fermentation and ageing.
How to limit Lactic Spoilage?
Simple precautions may be taken to avoid Lactic Spoilage:
Good cellar hygiene: This factor is critical to avoid cross-contaminations during fermentation and ageing of wines. Cellar material need to be cleaned thoroughly regularly.
Ensure a quick and complete alcoholic fermentation by controlling tank temperature and nutrients
Adding sulfites: reasonable use of sulfites on musts during harvest will delay the growth of lactic bacteria. A molecular SO2 value of 0.35 mg/L is considered efficient.
Temperature control during ageing. Keeping cellar temperature under 20 degrees Celcius will limit bacteria growth.
Monitoring through testing: Testing for residual sugars, pH and volatile acidity is good practice to manage the risk of lactic bacteria development.
If despite every precautions, lactic spoilage occurs, solutions exists. Cooling down wine tanks will limit bacteria growth. Adding sulfites will also stop bacteria proliferation. Wine can be filtered to remove lactic bacteria. Working with an oenologist will help you manage these operations.
Our Laboratory can help you prevent the occurence of lactic spoilage in your wine by simple testing. For example, determination of organic acids or microbiology testing will be useful to assess risks and plan operations accordingly. Professionals at OENOSCIENCE are alongside you in your product development. It is because of your support that we can inform you on industry trends. You have comments or suggestions? You would like to explore subjects in oenology? Contact us at info@oenoscience.com.
