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A Technical Guide for Wine Producers
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Nutrition During Rehydration - A New Approach To Yeast Nutrition
Introduction
The importance of nitrogen as a primary source of nutrition for yeasts during the process of fermentation cannot be overemphasised. The availability of assimilable nitrogen plays an important role in the tempo and course of the fermentation process. Insufficient quantities, or the depletion of the nitrogen available for assimilation, can result in sluggish and/or stuck fermentation, as well as the subsequent formation of H2S. The amount of nitrogen available for assimilation in must is mostly insufficient to support a successful fermentation, especially in high maturity grapes and the necessary adjustments at the right stage are therefore extremely important.
The role played by micronutrients in the optimal functioning of yeasts is a subject about which little has been known up to now, and has not received a lot of attention from researchers either. Recent research by Lallemand Inc., in collaboration with various international organisations, has shown, however, that apart from the huge impact of nitrogen, the role played by micronutrients during rehydration and the fermentation process in fact also makes a very important contribution to ensure a successful fermentation. The importance of certain micronutrients is discussed below.
Micronutrients Are Essential For Successful Fermentation
The role of minerals including Mg, Mn en Zn
Magnesium is essential for sufficient yeast growth and good metabolism. The availability of the Mg2+ ion plays a role, inter alia, in the phase and tempo of cell division of yeasts, as well as in the protection of the yeast cell against negative factors such as heat shock and ethanol toxicity. Magnesium also plays a very important role in the stability and permeability of membranes. On the other hand, if yeast experiences magnesium shortages, it may result in the production of higher levels of acetic acid and a lower alcohol tolerance.
Not only are the concentrations of magnesium important, but also the ratio of the available quantities of magnesium and calcium. If the quantities of calcium present in the growing medium exceed that of magnesium, it may result in the inhibition of magnesium transport through the plasma membrane. Furthermore high levels of calcium can also influence the fermentation activity of yeasts. In a process such as fermentation it is therefore important to minimise the antagonistic magnesium-calcium effect by manipulating the concentrations of these compounds in the particular medium. This may be obtained by not making calcium additions to the medium, and thereby ensuring a sustained high magnesium:calcium ratio.
Manganese plays a very important role in the metabolism of the yeast. When available in sufficient quantities, it supports protein and thiamin synthesis, which in turn contributes to the sufficient increase in biomass.
Zinc is a very important co-factor for certain enzymes. It also makes a positive contribution to the synthesis of riboflavin and protein. If zinc shortages occur, cell growth and fermentation activity will be hampered. In a medium where manganese shortages are encountered, even very low zinc concentrations will influence yeast negatively.
The role of vitamins including biotin, thiamin and pantothenic acid
Biotin is an essential vitamin in the carboxylation and decarboxylation reactions in yeast cells. If only insufficient quantities of biotin are available, cell growth may be limited and cell membranes damaged. It can also result in the excessive production of short chain fatty acids. Higher biotin levels are not usually associated with an increase in the fermentation tempo, but when nitrogen shortages are experienced, higher levels of biotin can accelerate the course of fermentation. Biotin also plays an important role in the production of higher alcohols and esters.
Thiamin fulfils an important role in the synthesis of isoleucin and valine. The addition of thiamin to fermentation limits the production of pyrovate, acetaldehyde and acetic acid. However, the addition of SO2 can counteract and even inactivate the effect of thiamin. This vitamin also ensures a successful completion of fermentation.
Pantothenic acid is considered essential for some strains of Saccharomyces cerevisiae, and it influences yeast metabolism under both aerobic and anaerobic conditions. It also forms part of the synthesis of Acetyl-Co-A, and is furthermore important in the production of fatty acids and amino acids. If pantothenic acid shortages occur, it may result in the production of sulphur components which obviously have a negative effect on wine flavour and wine aroma.
The role of amino acids
Amino acids plays an important role in a successful fermentation, since they function as the building blocks of essential proteins. Important proteins are taken up by the yeast from the surrounding medium, something which is usually occurring relatively early in the course of the fermentation process. Factors such as high ethanol concentrations and excessive applications of anorganic nitrogen such as di-ammonium phosphate (DAP) limits the further uptake of amino acids. It is therefore important for sufficient quantities of amino acids to be available to the yeast at an early stage. For this reason GO-FERM® provides the selected yeast with the necessary micronutrients, including essential amino acids, as early as during the rehydration stage.
GO-FERM® - A New Era In Yeast Nutrition
Recent research by the Lallemand group and some of its research partners, developed an entirely new approach to yeast nutrition. Results obtained in this way have shown that the application of specific micronutrients during the rehydration phase has an enormous impact on the continued and successful course of fermentation. The reasons for this are multiple, and include the following:
The pH of the rehydration water considerably exceeds that of the particular must and therefore provides a "friendlier" environment for the yeast. Clean rehydration water per se does not contain any SO2 either, and compounds such as, for example, organic acids and poly-phenols, which may initiate chelate formation, are absent. This means that all available micronutrients are made available to the selected yeast strain only. Furthermore the clean rehydration water does not contain any other micro-organisms that normally occur in must. On the other hand, the must has a low pH (of between 3 and 4), SO2 is possibly already present, it also contains certain compounds which may result in the formation of chelates and it obviously also contains the natural population of yeasts and bacteria. It is therefore clear that the clean rehydration water is an excellent medium for sufficient uptake of the micronutrients provided by the nutrient in question.
The product that has been developed as a result of the above research in order to address the early nutritional requirement of the yeast is known as GO-FERM®. It is 100% biological and consists of inactivated yeast cells that were grown especially for such use. The specific autolysis process ensures high levels of certain essential vitamins (thiamin, pantothenic acid, biotin), minerals (magnesium, manganese and zinc) and amino acids. GO-FERM® also provides small quantities of alpha amino nitrogen (approximately 10mgN/l with a 30 g/hl application). The use of Fermaid K as a complex nutrient is still necessary, especially in must with a very low nutrient status. For the best results it is recommended that GO-FERM® be used during rehydration and Fermaid K during the course of fermentation.
Application
GO-FERM® must be properly dissolved in the rehydration water at a concentration of 30 g/hl (calculated on the total volume that has to be inoculated) before rehydrating the specific selected yeast in it. When the yeast cells rehydrate, they take up the available micronutrients, also for later use as well. Considering that there is no competition for the uptake of these essential nutrients, the maximum is therefore made available to and taken up by the selected yeast strain.
Results
GO-FERM® ensures that fermentation proceeds smoothly, and the effect is clearly noticeable, especially towards the end of fermentation (figures 1 and 2). It also ensures higher cell counts and better cell viability (table 1), resulting in turn in better and faster utilisation of sugars.
The use of GO-FERM® satisfies the early accumulation of sufficient essential reserves and vitamins in the initial yeast population. This means that there are no micro-nutritional shortages and metabolic problems. The formation of negative metabolites such as volatile acids (table 2) and sulphur containing components is obviously limited.
Table 1. The effect of
Go-Ferm® on number of yeast cells and cell viability
after fermentation. Treatment Yeast
strain Number
of cells/ml after fermentation Number
of viable cells /ml after fermentation %
viable cells after fermentation Go-Ferm®
(30g/hl) EC1118 84
X 106 42
X 106 50 Control EC1118 66,6
X 106 28
X 106 42 Type
of must Fermentation Temperature
(oC) Yeast
strain Control (g/l
volatile acid) Go-Ferm®
[30
g/hl] (g/l
volatile acid) Chasan Chasan Chasan 18 24 28 EC1118 EC1118 EC1118 0,41 0,50 0,49 0,42 0,42 0,42 Chardonnay Chardonnay Chardonnay - - - 0,25 0,22 0,70 0,15 0,12 0,55
Conclusion
From the above results it is clear that the use of GO-FERM® has significant advantages for winemakers. It may find wide application, especially if the must contains very high sugar, if an altogether improved fermentation is required and for the preparation of sparkling wine, where yeasts have to function under extremely limiting conditions. GO-FERM® may be used in conjunction with any yeast strain.
NOTE: GO-FERM® is a product of LALLEMAND INC., with a patent pending. For more information, contact Piet Loubser at: Tel: +27- 21- 906 6688 or Fax: +27- 21 - 906 1790 or e-mail:ploubser@mweb.co.za
Sources Consulted
ANDERSON, G. 2002. A new era in wine and bacteria nutrition. The Australian & New Zealand Grapegrower & Winemaker. Annual Technical Issue, pp 144 - 148.
JULIEN, A. O., TRIOLI, G., & DULAU, L. 2002. A new approach to the integrated nutrition of oenological yeast. (an internal document).
LALLEMAND TECHNICAL DOCUMENTS 2001/2002.
LOURENS, K., & REID, G. 2002. Yeast nutrient management in winemaking. The Australian & New Zealand Grapegrower & Winemaker. Annual Technical Issue, pp 50 - 54.
OWN EXPERIMENTAL WORK IN COLLABORATION WITH ELSENBURG COLLEGE 2001 AND 2002 VINTAGES.
WALKER, G. 2000. The role of metal ions in optimising yeast fermentation performance. In: Nutritional aspects II. Synergy between yeasts and bacteria. Lallemand Technical Meeting 2000 Perugia, Italy. 27-30 April 2000.
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Piet Loubser, Lallemand South Africa, P.O. Box 3542, Matieland, 7602
e-mail: ploubser@mweb.co.za
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