It is normal for white foam or bubbles to appear during the secondary fermentation of wine. These white foam and bubbles are caused by the production of carbon dioxide during fermentation.

1, just fermented wine, filtered inside still contains a small amount of yeast in the role of the container surface, especially around the edges of the container has a lot of white bubbles this is a normal phenomenon. When the yeast inside is completely aged and dead, it will gather with the residual skin residue and precipitate at the bottom of the container to form yeast sludge.

2, white float to distinguish carefully, if a white film, and white bubbles, and even gray mycelium, that is stained with stray bacteria, fermentation failure, can not drink.

3, if a layer of white is the second fermentation of small bubbles entrained wine mud, will be a layer of delicate white film. When the secondary fermentation is over, the wine mud will naturally settle to the bottom of the bottle, not affecting the drinking.

Generally homebrewed wines don't pay much attention to this process, just leave it in storage and wait until the yeast sludge is formed, then take the supernatant and bottle it. The white floating material on the top, a very tiny layer, that is not filtered clean residual skin flakes gathered, generally does not affect the taste of wine, the end of the second fermentation, and then filtered once to be able to remove clean.

Expanded Information:

Wine production:

1. Crushing and de-stemming:

Crushing: separating the pulp from the juice.

Destemming: the fruit stalks have a green stalk flavor and are retained unless the wine requires additional tannins.

2. Alcoholic fermentation and maceration:

After the grapes are crushed and de-stemmed, they are transported to the fermentation vessel for fermentation. The yeast can be original to the grapes themselves or added artificially, and the fermentation process lasts for 4 to 10 days, when the tannins and pigments in the skins penetrate into the must.

The process of summarizing the tannins and pigments is called maceration. The duration of maceration varies from a few days to a few weeks. In the case of "new" wines, which are low in tannins and smoother, the maceration time is very short; in the case of long-lasting red wines, which require sufficient tannins, the maceration time is very long.

3. Changing the container and pressing the pomace:

The container is changed in order to separate the pomace from the original wine and end the maceration process. After the pomace is removed from the container, the wine is pressed. The wine pressed from the pomace is darker in color and has a higher tannin content and a bitter taste.

4. Malolactic Fermentation:

During the red winemaking process, a sub-fermentation called malolactic fermentation is usually carried out. Sub-fermentation uses lactic acid bacteria to turn the sour malic acid in the wine into a smoother and more stable lactic acid.

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