Making a Malolactic Starter Culture
Wyeast 4007 pure liquid malolactic bacteria culture 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. Sterile juice (grape, pear, or apple) diluted 1:1 with sterile water is an excellent media. Additions of nutrient (Yeast Extract or other ML nutrient) and pH adjustment (4.0-4.5) will be beneficial.
If a culture is to be expanded in sterile juice, then the culture can be added by itself. If the culture is to be expanded in non-sterile must, then it is best to utilize a co-culture method where yeast is inoculated at a low level (103 to 104 CFU per mL) at the same time as the addition of the malolactic bacteria culture at a level of 107 CFU per mL. This provides some protection from growth of undesirable organisms as well as allowing the bacteria to become acclimated 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 apple 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 70-75 °F (21-24 °C)
- Inoculate starter with 5-10% pure liquid malolactic bacteria and if a co-culture method is to be used, add the yeast at this time as well.
- Maintain temperature at 70-75 °F (21-24 °C) for 7-10 days. Very light CO₂ production will be visible and the turbidity should increase over the 7-10 days.
- Add starter to wine