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How Wine Yeast Benefits from Nutrients

What are yeast nutrients? | Why should I care about nutrients?
Nutrient dosage rates and timing | Conclusion | References

Imagine that you're about to participate in a great test of physical endurance - the New York City Marathon. Would you attempt such a feat knowing you hadn't eaten anything the night before? Of course not! And yet, without realizing it, many home winemakers are asking their yeast to perform a similar Herculean task without the benefit of basic nourishment.

From the perspective of wine yeast, it takes a lot of energy to fully ferment a quantity of grape juice into wine. As concerned winemakers, we must do our utmost to ensure the fermentation environment provides all the nutrients the wine yeast needs - when it needs it.

This winemaking article will explain the ins and outs of adding nutrients to your wine - how much to add, and when to add it.

What are yeast nutrients?
For our purposes here, we'll broadly define a "nutrient" as anything your wine yeast needs in order to survive, ranging from food, vitamins, and chemicals to the air and everything in between.

Luckily, yeast nutrients are inexpensive and easy to obtain for the home winemaker. They come packaged in a variety of formats. The most common formats are described below:

  • DAP (Diammonium Phosphate) - Contains fermentable nitrogen (N) at 25g/HL = 50mg/L N and phosphorus. The chemical formula for DAP is (NH4)2HPO4. For instance, a DAP addition of 1 g/L (8.3 lb/1,000 gal) provides about 258 mg/L fermentable N.
  • Fermax™ - contains diammonium phosphate, dipotassium phosphate, magnesium sulfate, autolyzed yeast. Grapestompers.com stocks this popular nutrient "cocktail".
  • Fermaid - Also called Fermaid K. Contains a variety of compounds such as amino acids, sterols, yeast hulls, and vitamins; also contains a limited concentration of fermentable nitrogen (25g/HL = 25 mg/L fermentable N)
  • Yeast Hulls - The cell walls of the hulls absorb autotoxic yeast byproducts that could inhibit alcoholic and malolactic fermentations. You would use yeast hulls by themselves if you encountered a stuck or sluggish alcoholic (normal) or malolactic fermentation.

Note: The rules allow an addition of 8 lbs of DAP per 1000 gallons of wine, but in addition, the full amount of vender's recommendation of proprietary mix (Fermax™, Fermaid, etc.) is also allowed.

Why should I care about yeast nutrients?
If your wine doesn't have enough nutrients in it for the yeast to work, you might end up having a stuck fermentation. Worse yet, you may even ruin your wine due to hydrogen sulfide contamination (a symptom of which is a "rotten egg" smell) caused by a lack of nitrogen and a vitamin known as pantothenic acid.

Here's a short list of the various nutrients needed by wine yeast, and the benefits each provides:

  • Nitrogen - Nitrogen produces the protein needed to make new yeast cells.
  • Oxygen - Oxygen is required during the initial phase of fermentation to help the yeast cells multiply rapidly, thus giving your fermentation a good kick start. The yeast also needs oxygen to produce lipids in their cell walls, to provide protection against the alcohol toxicity near the end of fermentation. The best way to accomplish the introduction of oxygen is to leave off the airlock for the first couple of days.
  • Micronutrients - The term given to various trace vitamins and minerals needed in small quantities, such as phosphorus, urea, amino acids, pantothenic acid, citric acid, biotin, yeast hulls, etc.

Nutrient Dosage Rates and Timing
There's definitely a right way and a wrong way to add nutrients to your must or wine. This is one time you don't want to do a "dump and run" by throwing in the complete dose of nutrients at one time at the start of your batch. Recent studies show that spreading the nutrient doses out over time - that is, properly spaced apart - can greatly benefit your wine. Moreover, there is evidence that suggests when DAP should be added versus Fermax™ or Fermaid K.

A recent post on the Enologists web board by Ed Goist suggests the following dosage recipe:

  • Before yeast addition: Add 50% of DAP dose and 33% of Fermax™ dose
  • Once fermentation starts: Add 50% of DAP dose and 33% of Fermax™ dose
  • At 12-8° Brix: Add the final 33% of Fermax™ dose

Dosage charts are shown below.

We add our doses in this way because one large initial dose of DAP may delay or inhibit the uptake of amino acids by the yeast cells. Also, if nitrogen is added too late, the cells can't uptake the nitrogen due to the presence of alcohol. Adding nutrient supplements such as Fermax™ or Fermaid K all at once can lead to too fast of a fermentation rate and an imbalance in uptake and usage of nitrogen compounds. Supplements added too late (after half the fermentation) may not be used by the yeasts, partly because the alcohol prevents their uptake. Thus, we spread out the doses over time it so the wine gets what it needs when it needs it.

What is a proper dose of DAP and Fermax™ for a wine?
The answer largely depends upon the source and quality of your juice. In general, if you press your own grapes or buy fresh or frozen juice from a vineyard, your doses will be higher than if you make your wine from a wine kit.

If making wine from fresh or frozen juice (not processed - just straight grape juice), here are the recommended doses of DAP and Fermax™:
- 1 gram DAP / liter
- 1 gram Fermax™ / US gallon

If making wine from a wine kit*, the proper doses would be:
- 0.2 to 0.4 grams DAP / liter
- 0.1 to 0.2 grams Fermax™ / US gallon

For example, let's say you have 6 US gallons of fresh grape juice from your backyard that you want to make into wine. Based on the chart above, your recommended doses would be calculated like this:

1 US gallon = 3.79 liters, so 6 gallons = 22.71 liters
Total DAP dose: 22.71 grams
Total Fermax™: 6 grams

Following our dosage recipe, we would add:
- 11.35 grams of DAP and 2 grams of Fermax™ before adding yeast
- 11.35 grams of DAP and 2 grams of Fermax™ once fermentation starts
- 2 grams of Fermax™ at 12-8° Brix

During our research for this article, we've discovered that the bare minimum level of fermentable nitrogen needed for fermentation is 140 mg/liter; the normal range is considered to be between 225 and 275 mg/liter of fermentable nitrogen.

A more exact means to determine the proper amount of nitrogen (and thus DAP) to add is to first measure the amount of nitrogen that is available in your must. You can calculate this value by performing a Formol titration. After you know how much nitrogen is in your must, you can easily figure out how much more you might need.

*Some juice in cheaper wine kits can be very low in nutrients and low in solid matter that usually assists in keeping the yeast in suspension even during active fermentation. Another factor to consider regarding juice from concentrate and kits is the fact that there is usually very little to no insoluble, particulate matter present. The absence of particulate matter allows the yeast to settle rapidly during the period that there is very little fermentation activity. This is especially true with cool temperature fermentations.

We've never experienced the problems described above with the kits made by RJ Spagnols. Tom has spoken with their staff to ensure the proper amounts of nutrients are present in each wine kit we sell.

Lallemand (a manufacturer of wine yeasts) recommends stirring the must several times during the first 24 - 48 hours and again during the last days of fermentation to keep the yeast up in suspension where all of the action is.

Conclusion
Nutrients for wine yeasts - when added in the proper amount and at the correct time - will go a long way towards preventing common problems (such as stuck fermentations and hydrogen sulfide contamination) and help ensure your wine ferments fully and without difficulty. Nutrients are available in several formats and are inexpensive to purchase; with a little knowledge and basic math skills, it's easy to determine the proper dose of nutrients to add.

References
Clicking on any of the reference links below will open a new browser window:

Enologists - A group focusing on the science and art of winemaking at any level. Anyone interested is encouraged to join!
http://home.att.net/~lumeisenman/chapt12.html
http://winemaking.jackkeller.net/qa.asp
http://www.vinquiry.com/pdf/nutrient_additionsQ.pdf
http://www.vinquiry.com/pdf/FermaidK.pdf
http://www.scottlab.com/nutrient.htm
http://www.scottlab.com/fermaid_k_balanced_nutrition.htm
http://www.fst.vt.edu/Zoecklein/july-aug00.html
http://www.fst.vt.edu/Zoecklein/Fermentationissues.html
http://www.makewine.com/makewine/nutrients.html
http://www.vawa.net/hydrogensulfide.html
http://consumer.lallemand.com/danstar-lalvin/InFerment/Cider.html
http://consumer.lallemand.com/danstar-lalvin/winefaq.html
http://consumer.lallemand.com/danstar-lalvin/fermaidwine.html

 

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