Wednesday, April 25, 2012

Fermentation Nutrients

Wine yeast have a high demand for nutrients, not only during rehydration, but also throughout fermentation. Nitrogen deficiency is the most common cause of fermentation problems, but also the most easily remedied (nitrogen deficiency will be discussed in a later post).

Micro-nutrients (sterols, lipids, vitamins, and minerals) are naturally occurring in grapes, but are also commonly deficient in juice/must. Unfortunately, such deficiencies are not typically identifiable prior to fermentation, meaning winemakers have a difficult time forecasting their corresponding negative effects on wine quality; that being said, one can usually guarantee problems with such micro-nutrients if grapes have been subject to poor growing conditions (mold/rot) or have a history of deficiency. Fermentation nutrients are a class of products that help remedy these deficiencies and can be classified into two different categories: complex yeast nutrients and vitamin supplements.

Complex yeast nutrients such as Fermaid K/O, Bioactiv, and Superfood, are proprietary blends of nutrients; many provide some level of nitrogen (whether inorganic, organic, or both), but all provide sterols, fatty acids (lipids), and vitamins (thiamine, biotin, etc.) at varying levels. Inactivated yeast cell walls present in these products absorb medium-chain fatty acids that are toxic to yeast, helping prevent alcohol toxicity and yeast stress that would lead to undesirable aroma and flavor development. They also provide nucleation sites that help keep the yeast in suspension throughout fermentation. Winemakers have varying views on when, why, and how to use complex yeast nutrients (% additions at different stages throughout ferment, combination of more than one product, only for stuck ferments, etc.). I have used them in most of my winemaking experiences and believe they are very beneficial, if not essential in many cases, to successful fermentation.

Vitamin supplements, such as Cerevit and Vitamix, provide an array of key nutrients such as thiamine, biotin, nicotinamide, magnesium sulphate, calcium panthothenate, and folic acid. Though many of these micro-nutrients are contained in complex yeast nutrients, they can still be at deficient levels. Vitamin supplements help ensure that undesirable sulfur compounds are not created due to yeast stress. Again, winemakers all have varying views on when, why, and how to use vitamin supplements (at certain brix levels, only with problem ferments, etc.); the main thing is to make sure that legal levels of certain micro-nutrients are not exceeded, particularly when using vitamin supplements in conjunction with out yeast nutrients (for example, Cerevit added at its recommended rate contains the legal limit of calcium panthothenate). With any hint of a problem or for higher price-point wines, I recommend using vitamin supplements as a safety precaution for several reasons: they don't add a whole lot of money to your production expense, don't effect aroma/flavor, and give you peace of mind.

Check out these related links: Yeast Rehydration NutrientsSuccessful Wine Fermentation - Introduction, Selecting the Right Yeast (Part I, Part II), Preparing Juice/Must for Fermentation, Indigenous Yeast, Inoculation, Yeast Propagation (Part I, Part II, Part III).

2 comments:

  1. I and my friends really like the wine discussions, Mike.
    Is it silly for us to think of growing our own grapes in our backyard and making our own wine in our basement? Just for fun, learning and personal consumption.

    ReplyDelete
  2. Thanks Jim. I wouldn't say it's silly at all, as long as you have the space to dedicate to vines; need to have a decent amount of grapes to get enough juice to ferment adequately. Send me an e-mail and I can give you some details if you're interested. Maybe a sort of co-op with some like-minded neighbors would work well?

    ReplyDelete