Lena Savoie
Wild yeast is a mix of different yeasts and organisms that feed on sugar, creating various outcomes. It is often used in winemaking, with the most common type being Saccharomyces cerevisiae. Wild yeast typically produces 3-6% alcohol, but this can be influenced by factors such as the type of yeast and the presence of other bacteria. To increase alcohol content, one can reduce bacterial growth, use specific yeast strains, or employ techniques like jacking to increase the ABV of the final product.
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What You'll Learn
Use a yeast with higher alcohol tolerance
The use of yeast with higher alcohol tolerance is a crucial strategy to force higher alcohol content in wild yeast fermentations. Here are some detailed instructions and considerations:
Firstly, it is important to understand that yeast, being a single-celled organism, has specific conditions under which it can grow and reproduce. One critical factor is the presence of alcohol. Each yeast strain possesses an alcohol tolerance limit, beyond which the yeast cells become dormant and cease fermentation. This limit is typically expressed as a percentage of alcohol by volume (ABV).
To achieve higher alcohol content, selecting a yeast strain with a higher alcohol tolerance is essential. Most major yeast suppliers provide alcohol tolerance data for their yeast strains, although this information may be buried in specification sheets. BeerSmith 3, for example, is a software application that includes a yeast database with alcohol tolerance information for various strains, making it easier to choose a suitable strain for your needs.
When choosing a yeast strain, it's worth noting that alcohol tolerance can vary depending on several factors, including yeast health, available nutrients, sugar levels, and the specific yeast strain. Therefore, it is recommended to select a strain with a higher alcohol tolerance than your desired ABV to ensure successful fermentation.
Additionally, wild yeast strains, such as those found in vineyards, can exhibit higher alcohol tolerance. Yeast collected from grape skins or elderberries, for instance, may have an alcohol tolerance of around 10-14% ABV. This can be a more unpredictable process, but it offers the potential for higher alcohol content.
Lastly, combining wild yeast with commercial yeast strains can be a strategy to increase alcohol content. By adding domesticated yeast to your brew and allowing it to remain open for a while, the domesticated yeast may outcompete the wild yeast and other organisms, resulting in a higher ABV. However, this method may also produce some unexpected flavours along the way.
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Reduce bacterial growth
The use of wild yeast in fermentation can lead to varying alcohol levels due to the unpredictable nature of wild yeast, which can be a mix of different yeasts and organisms. To force higher alcohol levels, one approach is to reduce bacterial growth, as yeast and bacteria compete for the same sugars. Here are some ways to reduce bacterial growth and promote higher alcohol content:
Firstly, the collection of wild yeast from locations where "good" yeast thrives, such as raspberry patches or grapevineyards, can improve the odds of achieving higher alcohol levels. Yeast from berries, particularly grapes, tends to have a higher alcohol tolerance.
Secondly, the addition of sodium chloride (NaCl) and ethanol has been shown to decrease bacterial growth and improve yeast growth. This combination can give yeast a competitive advantage by creating conditions that selectively favour yeast over bacteria.
Thirdly, acid-washing yeast cells with diluted sulfuric acid before and after fermentation can help reduce bacterial contaminants without negatively affecting yeast growth. Specifically, a sulfuric acid solution with 5% ethanol (pH 2.0) is effective in removing bacterial growth while maintaining yeast viability.
Additionally, bacteriophage-encoded lytic enzymes, such as the endolysin LysA2, can be used to control bacterial contamination. LysA2 has been shown to reduce the growth of a wide range of lactic acid bacteria (LAB) without impacting yeast growth, making it a valuable tool for reducing bacterial competition during fermentation.
Finally, while not a direct method of reducing bacterial growth, selecting yeast strains with higher alcohol tolerance can help achieve higher alcohol levels. Some yeast strains, like those found on elderberries or the yeast Zygosaccharomyces, can tolerate alcohol levels of up to 15% or even higher, depending on winemaking styles.
By implementing these strategies, you can reduce bacterial growth and promote higher alcohol content in wild yeast fermentations.
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Harvest yeast from grape skin
Harvesting yeast from grape skin is a simple process, but it requires attention to detail and a sterile environment to avoid contamination. Here is a step-by-step guide on how to harvest yeast from grape skin:
First, source your grapes. It is important to use organic grapes to avoid any chemical residue, such as pesticides, herbicides, or fungicides, that may be present on conventionally grown grapes. If using store-bought grapes, ensure they are organic and give them a gentle rinse before starting.
Next, you will need to prepare your equipment. Gather a sanitized container, such as a glass jar or bottle, and a sterile glove if you wish to avoid direct contact with the grapes. It is crucial that your equipment is sterile to prevent the growth of unwanted bacteria or fungi.
Now, you are ready to handle the grapes. Wearing your sterile glove, gently rinse the grapes in a bowl of water to remove any dirt or residue. You don't want the grape juice, as it is the yeast on the outside of the grapes that you are after. Continue rinsing the grapes until they look shiny and free of any visible residue.
Once your grapes are clean, place them into your sanitized container. For a standard-sized jar or bottle, 20 grapes should be sufficient. Cover the container with aluminium foil or a loose-fitting lid to allow airflow while also preventing contamination.
At this point, you may choose to add a small amount of sterile liquid to your container, such as distilled water or apple juice, to create a starter solution. This is not necessary, but it can help encourage yeast growth and activity.
Leave your setup in a warm place and wait several days. Check your container periodically to observe any changes. You are looking for signs of yeast growth, such as foaminess or a change in texture. If you notice any foul odours or suspicious growth, discard the contents and start over, as this may indicate bacterial contamination.
Once you observe yeast activity, you can transfer your wild yeast culture to a larger container with additional starter solution to propagate your yeast further. From here, you can begin experimenting with your wild yeast in various fermentation processes, such as brewing or baking.
It is important to note that wild yeast is unpredictable, and the alcohol tolerance and flavour profiles can vary greatly. Harvesting yeast from grape skins can be a fun and rewarding project, but it may take some trial and error to achieve your desired results.
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Use cultured yeast
Using cultured yeast is a popular method for achieving higher alcohol content in winemaking. Cultured yeast strains have only been used in winemaking for the past century, but their predictable fermentation capabilities and high alcohol tolerance make them a preferred choice for many winemakers.
The most common cultured yeast used in winemaking is Saccharomyces cerevisiae, which has a predictable and vigorous fermentation rate, can tolerate relatively high levels of alcohol (up to 15% or more) and sulfur dioxide, and thrives in the typical wine pH range of 2.8 to 4. Winemakers select this yeast strain for its dependability and ability to completely utilize all fermentable sugars, resulting in a higher alcohol content.
Other benefits of using cultured yeast include low foaming during fermentation, minimal production of undesirable compounds like pyruvate and acetic acid, and ease of racking, fining, and filtering. Cultured yeasts are also deliberately grown in commercial labs under specific conditions to enhance their survival factors, ensuring a higher likelihood of successful fermentation.
When choosing a cultured yeast, winemakers must consider the type of grape and wine being produced, as different yeast strains will impart unique characteristics to the final product. For example, some strains may produce fruity aromas, enhance mouthfeel, or have the ability to ferment in low temperatures or high acidity.
While cultured yeast provides more control over the fermentation process and alcohol content, some winemakers still prefer wild yeast for the unique flavours and characteristics it imparts to the wine. Wild yeast is also favoured by some for its contribution to the expression of terroir in the wine, particularly in renowned wine regions such as Bordeaux.
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Increase sugar content
The amount of alcohol produced by wild yeast depends on the type of yeast, and the presence of other organisms. Wild yeast often shuts down at 3-6% alcohol by volume. To increase alcohol content, you can increase the sugar content in the mixture. Here are some ways to do this:
Collect Yeast from Fruit
Collecting wild yeast from fruits such as grapes, elderberries, or raspberries can increase the chances of obtaining yeast with higher alcohol tolerance. Yeast from vineyards or grape skins can have an alcohol tolerance of 10-14%, while yeast from elderberries and other berries is also known to be more alcohol-tolerant.
Use Sugar or Honey
Adding sugar or honey to the mixture can boost the alcohol content. Wash grapes or other fruits and put them in a container with sugar, honey, and water. This will increase the sugar content available for the yeast to convert into alcohol.
"Jacking" the Wine
If your wild yeast produces wine with a low ABV, you can try "jacking" the wine. Place the wine in a freezer until it appears frozen. Turn the container upside down and collect the first 1/3 of the liquid that forms. This portion will have a higher concentration of alcohol and sugar, resulting in a higher ABV.
Reduce Bacterial Growth
Since bacteria and yeast compete for the same sugar source, reducing bacterial growth can lead to a higher proportion of yeast and, consequently, increased alcohol production. This can be achieved by taking specific measures during the fermentation process to discourage bacterial growth.
It is important to note that the results of using wild yeast can be unpredictable, and the ABV achieved may vary. The methods mentioned above can help increase the chances of obtaining a higher alcohol content, but the specific type of wild yeast and the conditions of fermentation will ultimately determine the outcome.
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