In these series of posts, we will introduce you to the basic problems many winemakers face when making their wine, how and why these problems happen and how the yeast biocapsules can be applied to help these cases!

Series #1 Stuck Fermentation

What is stuck fermentation?

Stuck fermentation is when fermentation has stopped abruptly or is progressing too slow to be for practical purposes. This leaves the wine to have higher than intended sugar concentration and the wine becomes an incomplete product, since winemakers are looking to get their wines less than 2 g/L for it to be considered a finished fermentation. Stuck ferments also tend to come with other problems, such as high risk of microbial contamination, off-aromas and a huge loss in time.

What causes stuck fermentations?

Imagine a doctor treating a patient who has a high fever. Could it be the flu? An underlying disease? An allergic reaction? Or a viral infection? All these are possible causes which will have different medications and treatments. Just like a doctor assessing an ill patient, a winemaker has to assess a stuck ferment. However, in the winemakers case, the wine will not talk to him/her about its symptoms and problems in words. Rather, the symptoms are expressed by smells (often bad or rotten-like) and appearance (discolored or murky). A good winemaker will monitor closely each ferment and will quickly be able to assess the wine’s problem by these signs. Some common problems are because of:

    • Erroneous yeast handling
    • Nitrogen deficiency
    • Lack of oxygen
    • Glucose to fructose ratio imbalance
    • Nutritional imbalance
    • Bad temperature management
    • Lack of nutrition (minerals, vitamins, sterols, organic nitrogen)
    • Inhibitory metabolites
    • Microbial contamination

How can we solve stuck fermentation?

Restarting a once stuck ferment is a challenging task, especially because the cause of the problem could be one or multiple different factors. Aquí hay algunos consejos para tratar un fermento atascado.

Add new fresh yeast.. A good candidate is a yeast strain that has high alcohol tolerance and is robust fermentor. Since the stuck fermented wine most likely has converted some of its sugars to alcohol already, the new yeast must be able to tolerate this. Also consider a yeast that has a strong affinity to fructose, which would most likely be the simple sugar left over in higher quantity in your wine.

Add yeast hulls. Yeast hulls are remains of dead yeast cells that are able to absorb any toxic compounds that have led to your stuck ferment. Short and medium chain fatty acids or pesticides can be toxic for yeast and it can stop the fermentation or get in the way of any new yeast that are restarting the fermentation

Use yeast biocapsules. Yeast biocapsules make it easy for you to switch out non-fermenting yeasts with active yeasts. Simply extract your old yeast biocapsules and put in new ones to get your ferment going again.

References:

Bisson, L.F., 1999. Stuck and sluggish fermentations. American Journal of Enology and Viticulture,50(1), pp.107-119.

Henschke, P.A., 1997. Wine yeast. Yeast sugar metabolism, pp.527-560.