Malolactic fermentation (MLF) is crucial to making almost all red wines and some whites and sparklings as well, because it stabilises the wine. MLF removes the malic acid that can be a carbon source for yeast and bacteria, leading to some unwanted flavours.
Traditionally, winemakers waited until after yeast-driven fermentation had been completed before beginning MLF. Then studies started to explore the option of doing the two together, as tends to happen with uninoculated ferments. Today, there are a range of options and winemakers make a decision based on what they like and what they are trying to achieve.
Dr Eveline Bartowsky, a Senior Research Microbiologist at the Australian Wine Research Institute (AWRI), spends a great deal of her time assessing MLF options and techniques and helping winemakers make choices that suit their needs.
These are her top 10 tips for effective MLF.
1. Check the key parameters
Start with the basics. The four classic parameters – alcohol, pH, sulfur dioxide and temperature – are still the essential first things to check to help ensure things go to plan.
2. Know your history
If you are aware that a particular parcel of fruit is consistently difficult to get though MLF, take time to consider the wine parameters and then tweak if necessary to help the bacteria complete the process.
3. Be clear about your plans
Your approach to MLF and the decisions you make must be appropriate for the wine style you want to make (because the MLF process contributes quite a lot). MLF takes time and effort, so make sure you use it to its full potential.
4. Understand the sensory impact
This is one of the most important parts of the planning, because the many bacteria strains available have quite different sensory impacts. Make sure you build this into your thinking or you might have a successful MLF process, but not quite the wine you want.
5. Choice 1: Yeast / bacteria compatibility
A lot of research has demonstrated the importance of yeast and bacterial compatibility for a successful MLF. It’s important to get it right, as some yeast will produce compounds that are toxic towards bacteria.
6. Choice 2: Bacterial strain
Select a strain that suits your wine – in particular, one that is tolerant to the wine’s composition. A large number of O. oeni strains are now available, with different winemaking properties and characteristics (e.g. tolerance to red and white wine composition) and metabolisms (sensory influence). There are also a couple Lactobacillus plantarum strains that might suit your winemaking style.
7. Choice 3: Pass the butter?
Consider if you want a buttery character (diacetyl) or not. This sensory feature might suit a particular wine style or market niche. This can be managed quite easily through MLF management.
8. Take your time
Prepare the bacterial culture carefully. Follow the instructions (no cutting corners) and, if necessary, consider taking the time to adapt a culture to your wine.
9. Try to save time
Co-inoculation (or simultaneous inoculation; inoculating bacteria early during primary fermentation) is an effective strategy for reducing overall vinification time, as well as a means to help adapt bacteria to difficult wine conditions or wine style.
10. Make your own
Take advantage of using your ‘own’ strain that works well with your wine. The AWRI can help you with its management and storage.
The AWRI help-desk is a service provided to levy payers though Wine Australia funding and is accessible during business hours and contactable on 08 8313 6600 or by email: email@example.com.