Making a Malo-Lactic Starter Culture
Wyeast pure liquid malo-lactic bacteria cultures can be expanded for use with larger volumes through the use of a starter. Starter cultures are a common practice in the wine making industry.
What is a starter?
A starter is a term that refers to the process of expanding the volume of a culture by inoculating a volume of media and allowing it to incubate. The incubation period allows the culture to consume nutrients and carbohydrates in order to multiply. Once the culture has been allowed to expand (or multiply), it is ready to inoculate a larger volume of must.
How to Create a Starter Culture
Various media can be used for creation of a starter culture depending on available resources and technical capabilities. A good option is must or juice (grape, pear, or apple) diluted 1:1 with sterile water, adjusted to pH 4.0-4.5, with additions of nutrient (Wyeast Nutrient, or yeast extract). ML cultures have comlplex nutrient requirements and will not utilize synthetic sources of nitrogen found in DAP.
Growth can be improved by utilizing a coculture method. Yeast can be inoculated into the starter at a low level (103 to 104 CFU per ml) at the same time as the addition of the malo-lactic bacteria culture (107CFU per ml). This method has the benefits of protection from growth of undesirable organisms, providing an anaerobic environment, providing nutrients from yeast by-products, and acclimation to a low pH and alcoholic environment.
The starter should be sized to provide an inoculum that is 1 to 5% of the total volume of the batch. For example: A 1 gallon starter could inoculate up to a 100 gallon batch of wine.
The following is one example of a method for creating a starter culture:
- Dilute juice 1:1 with sterile water.
- Add 0.5% yeast extract by volume for nitrogen supplementation or use a ML bacteria nutrient
- Adjust pH to 4.0
- Bring must temperature to 70 to 75°F (21 to 24°C)
- Inoculate starter with 5-10% pure liquid malo-lactic bacteria and if a coculture method is to be used, add the yeast at this time as well.
- Maintain temperature at 70 to 75°F (21 to 24°C) for 7 to 10 days. Very light CO2 production will be visible and the turbidity should increase over the 7 to 10 days.
- Add starter to wine