Introduction
There are a number of products made from Inactive Dry Yeast (IDY) that are used in various ways in modern winemaking. Many claims are made about their properties and benefits, however not all these claims have been scientifically proven leading to some confusion amongst winemakers. This article looks at the proven benefits of these winemaking products.
How yeast based nutrients help produce better ferments
Stuck ferments still occur in many wineries. The causes are complex, however yeast nutrition is one of the most important and widespread reasons.
Until recently, diammonium phosphate (DAP) was the only yeast nutrient available. These days it has become a well established practise in many wineries to use what are commonly referred to as “complex yeast nutrients”.
There are a number of such complex nutrients on the market from a variety of large and small suppliers – some manufacture the raw materials whilst others simply blend them. Having a large library of yeast strains and their own research departments favours the bigger companies, giving them more choice of the most appropriate strains for this product development.
But is this use of such products necessary or even useful?
A recent scientific review revisited the causes of slow and stuck ferments and considered the benefits of using commercial IDY products (1).
To quote from that study “Saccharomyces yeast can use ammonium ion and amino acids for nitrogen sources. Low levels of yeast assimilable nitrogenous compounds…have been related to lower fermentation rates and longer fermentation kinetics, both considered the main causes of stuck or sluggish ferments. In addition, ethanol and …medium chain fatty acids can contribute to these phenomena”.
From the same review: “…increasing the sterol content of yeast promoted a more active fermentation by increasing the membrane permeability and allowing a higher interchange of substances between cell and the medium. Moreover… sterols could act as a survival factor, increasing the reserves that yeast could use during the decline phase”.
That is, to be effective in assisting fermentation, commercial products should contain nitrogen supplements and sterols.
Commercial yeast nutrient products may include a soluble fraction that contains amino acids and some also contain added DAP as a source of ammonium ion.
It is obvious that these nitrogen components could be of use in a nutrient deficient must and so claims of helping fermentation kinetics would appear justified.
Again it would appear that using yeast strains that have high sterol levels is also an advantage.
One product the author is familiar with, Maxaferm, is an example of a product that is formulated from inactivated yeast, yeast extracts, DAP and thiamine. The Saccharomyces strain chosen from the DSM library has maximal levels of the important ergosterols and zymosterols.
How yeast hulls assist with stuck ferments
Another yeast based additive that is used to assist with stuck ferments is yeast hulls. Can we be sure that there is a valid benefit in their usage?
Again from the review: “…yeast walls (hulls) have a great ability to adsorb a broad range of chemical compounds…(and ) may be used to remove some compounds that could inhibit alcoholic fermentation, such as short chain fatty acids (C6 to C11)”.
Yeast hulls have been shown to also enhance fermentations by releasing survival factors such as fatty sterols and long chain unsaturated fatty acids.
This type of product is therefore recommended to enhance the fermentation process as well as to help restart a sluggish ferment.
Studies on a commercial yeast hull product (DSM Extraferm) have also demonstrated that by choosing a suitable Saccharomyces strain, no yeast odour effects are transmitted to the wine, even at high dosage rates (2).
Other components in wine have been demonstrated to have been removed by yeast hulls. These include the mycotoxin Ochratoxin A (1), and some pesticide residues. More research is needed, however, to be able to fully understand the scope of the use and benefits of these preparations.
How wine can be tartrate stabilised by mannoproteins
One very interesting component of IDY is mannoprotein. Some fractions of mannoprotein have been used now for several years to provide tartrate stability without the need for cold stabilisation.
Using a component of Saccharomyces such as mannoprotein that is soluble and added just prior to bottling is a great advancement on the cold stabilisation technique which requires high energy use and has the undesired potential to alter the aroma of the wine.
In our laboratories we have been testing the stability of white wines using DSM Claristar mannoprotein for more than three years. These wines that are still tartrate stable after this time and show signs of some mouthfeel enhancing improvements.
What is Inactive Dry Yeast?
As mentioned the above types of commercial products are produced from a range of yeast based ingredients, particularly fractions of Saccharomyces cerevisiae. How are these fractions obtained?
As most winemakers know, allowing a ferment to become too hot can cause the yeast to die and the ferment to stop. This is the basis of the industrial process to produce IDY from active yeast. That is, IDY for use in wine is simply Saccharaomyces cerevisiae that has been inactivated by high temperature, that is, by thermal inactivation.
Types of IDY preparations
To help winemakers understand the use of IDY components it is worth considering what yeast based wine additive products are available.
There are many types of IDY preparations; however they can be grouped into the following four categories (1):
1. Inactive yeast
Whole yeast inactivated by thermal means as mentioned above.
2. Yeast hulls
Also known as yeast cell walls, yeast walls or yeast ghosts. Yeast hulls are the cell walls remaining once the cytoplasmic cell interiors have been extracted from the inactivated whole yeast cell.
3. Yeast extracts
The cytoplasmic degradation material left over from the extraction of inactivated whole yeast cell to produce yeast hulls.
4. Yeast autolysates
To recap Wine Science 101, yeast autolysis (also known as self-digestion) is the process of the destruction of the yeast cell by the action of its own enzymes. Yeast autolysates are the material left over from this autolysis process, which in practise involves thermal inactivation of the cells and then an incubation process.
Conclusion
The use of Inactivated Dry Yeast (IDY) is widespread in the wine industry, particularly in formulated yeast nutrient products. Many claims have been made as to the benefits of these products. Some scientific research that demonstrates some of the benefits of these products has been discussed, however more research work needs to be done to see if the many claims made are indeed valid.
There is sure to be many more applications of these components of yeast that will be developed in the future. An understanding of the derivation of the IDY components and the benefits of the resulting products is an important aspect of a winemaker’s knowledge base.
References
1. “Scientific evidences beyond the application of inactive dry yeast preparations in winemaking” Pozo-Bayon M. A. et al, Food Research International, 42, 2009, 745-761
2. Wine ingredient news, 05/2009, DSM Food Specialties, Delft, Netherlands
Article from the Australian and New Zealand Grapegrower and Winemaker, Issue 586, 2012
Page Number(s): 81-83
Author: Greg Howell
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