Skipping the Hydration Step in Fermentation: A new line of yeast strains that do not need to be rehydrated prior to being added.
I met with the Fermentis staff at the 2018 Unified Symposium to learn about the newer yeast strains they had recently released and the efforts they had taken with the E2U brand, in particular. The company's re-introduction of the E2U brand was part of a program to reevaluate their entire yeast product line and to understand how their yeasts strains perform in a wide range of fermentation sources that are different from their primary target.
Etienne Dorignac, technical manager of Fermentis, headed a project starting in 2016 to characterize many of the properties of the company's yeasts to ensure that the strains would produce the appropriate aromatic and structural elements in a reproducible manner in the wine, while also meeting the E2U mandate to be simple to use.
A summary of the E2U process
A symposium at the 10th edition of Enoforum in Vicenza, Italy, (May 16-18, 2017) included a discussion of the E2U process. The following summary of the E2U process is based on a YouTube video of that symposium.
In the process of industrial yeast strain preparation, the first step is to find a strain of yeast that has the characteristics needed for the desired wine style. Once the strain is identified, the yeast production company has to design a method to grow the strain in a culture and environment that will create the largest biomass in a healthy state. The goal is to synchronize the growth of the yeast so that the majority of the yeast culture can be harvested at the ideal time--when the cells can be preserved in optimal condition for regrowth in the wine. From the standpoint of the yeast producer, this is where the rubber hits the road.
As winemakers we understand that the rehydration stage is when yeast is at its most delicate and fragile condition in the fermentation process. We know that small errors in this process can significantly affect the growth of the yeast in the fermenter and therefore affect the quality of the wine.
The drying process must carefully reduce the moisture in a way that preserves the yeast membranes. One of the significant components of yeast membranes are phospholipids. These elements give the structural support to the membranes upon rehydration. Typically, winemakers add yeast hulls to the rehydration mixture of the yeast. These hulls release sterols available to be absorbed by the freshly rehydrated yeast thus strengthening their membrane structure. Helping the cell walls at this stage provides the initial vigor necessary to adjust to the osmotic pressure the sugars present and then the toxic effect the ethanol presents to the yeast throughout the fermentation.
Dehydrating yeast too quickly can crystalize the phospholipids, which will destabilize the yeast membrane on rehydration, because as the yeast cells are dried, the cell shrinks in size from its fully hydrated state and it bends into overlapping folds. To ensure the best resistance to the drying process, Fermentis shapes the yeast in order to get, among others, a high trehalose content. This tactic provides structural help to the yeast cells and provides protection against the phospholipid crystallization.
The company also adds an emulsifier to the yeast as they are drying to provide additional help in the process of drying and later rehydration. The emulsifier is a plant oil that aids water transport into the cells. A fluid bed dryer is utilized during the drying process so that the cells are dried in a gentle manner in order to protect them as much as possible.
Fermentis validates the drying process by rehydrating some of the yeast cells in a sugarwater solution at temperatures ranging from 10[degrees]C to 30[degrees]C while assuring their residual viability. Micro-vinifications are conducted to confirm the aromatic and structural characteristics and to be sure nothing has changed in their organoleptic qualities.
The E2U process encompasses two parts: industrial production of sustained genetic, physiological and structural qualities, and then the creation of a dried product that can withstand the rigors of rehydration. Informational materials published by Fermentis include fermentation curves comparing standard rehydration methods of the same strains with those following the E2U protocols. The results show that both the standard methods and the E2U protocols to have the same performance characteristics.
The yeast review project
As of 2018, the E2U group of yeast encompasses seven different strains with different characteristics, which gives the winemaker a range of choices for products as varied as sparkling wines and high alcohol wines. Some strains express strong thiol production, while others express strong ester production. There also is a mix of nutrient requirements from low to high levels.
As part of the project started in 2016, Fermentis compared the performance of different yeast strains with respect to many organoleptic and analytic qualities with nutrient conditions. Figure 1 shows the analytic results in a set of three graphs. Figure 1 shows the Odor Active Value (OAV), which is a compounds concentration/perception threshold. These values are standardized on a 0 to 10 scale. Note that the SafCEno GV S107 and the SafCEno VR 44 are not E2U in all three graphs in Figure 1.
Comparison of Figure 1a with Figure 1b demonstrates the effect of Yeast Available Nitrogen (YAN) deficiency with that deficiency corrected in lb from the nutrient level of 1a. In the case of Figure 1b and 1c, ethyl esters were enhanced at varying levels, no matter whether YAN was deficient and corrected or if YAN was normal and additional nutrients added. These graphs indicate that the ability of the yeast to add additional compounds is strongly linked to nutrient concentration and, therefore, can be controlled by the winemaker.
The organoleptic results are shown in spider graphs in Figure 2. These results are quite different when compared with the analytical results. For example, the thiols with YAN deficiency and recommended adjustments in Figure 2b show marked decreases in Fresh/Ripe Fruits and Reduction/Oxidation and increases in Fruity/Amylic, Vegetal, Floral and Mineral characteristics. The esters on the right side of the spider graph in Figure 2c are generally enhanced in all traits on the Reduction/Oxidation and Fruity/Amylic axis and virtually nonexistent on the left side.
This set of conditions shown in both figures indicate that winemakers have control over a wide range of aromas, flavors and the balance in the wines produced with these strains.
An independent yeast trial
Fermentis provided SafCEno HD S135 and SafCEno CK S102 yeasts so that I could conduct independent lab trials. March and April are not the best months to do fermentation trials, and consequently I was not surprised to have variable results on small scale fermentations. The good news was that the lab trials generally followed the data from the curves presented at the EnoForum meeting discussed above.
Fortunately, I did have a client who needed a larger scale fermentation (2,000L) for both white and red wines. These two wines were inoculated with dry yeast at the recommended rates. The juice was clarified juice, which may have been the cause of a bit longer delay in the beginning of fermentation. The temperature at the start of fermentation was 51[degrees]F and ended at 64[degrees]F 21 days later. The Brix level did not show any drop for the first five days, although signs of fermentation occurred during the fourth day.
From that time forward, the fermentation followed the normal protocol of what was to be expected. We added yeast nutrients at one third and two-thirds Brix depletion and the fermentation finished at -1.08[degrees] Brix. These fermentations were conducted on American grape varieties, and the resulting aromas and flavors were as expected from these varieties. Because these grapes have very strong aromas to begin with, I can't say definitely that there were additional aromas contributed to these fermentations, but there may have been some aromatic components contributed.
In the future, I would like to see this different type of fermentation protocol conducted using vinifera or hybrid grape varieties and at the normal time for harvest and fermentations. With a significant increase in solids potentially provided by more yeast hulls or leaving some natural grape juice solids, the delay in the start of fermentation might be less of an issue.
Richard Carey is a wine consultant and owner of Tamanend Wine in Lancaster, Pa. He is a regular contributor to Wines & Vines.
Fermentis has developed new yeast strains that do not need to be rehydrated to conduct a fermentation.
A plant-based emulsifier and fluid bed dryer provide a gentle drying process to protect yeast cells.
A small scale trial fermentation finished dry with expected flavors and aromas.
Please Note: Illustration(s) are not available due to copyright restrictions.
Caption: Figure 1a (top): Matrix Thiols/Esters. Figure 1b (bottom): Matrix Thiols. Figure 1c (top): Matrix Esters.
Caption: Figure 2a (left): Matrix Thiols/Esters. Figure 2b (middle): Matrix Thiols. Figure 2c (right): Matrix Esters.
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|Comment:||Skipping the Hydration Step in Fermentation: A new line of yeast strains that do not need to be rehydrated prior to being added.(WINEMAKING)|
|Publication:||Wines & Vines|
|Date:||Jul 1, 2018|
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