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New World Wine Maker Blog - yeast nutrients

Yeast Rehydration Nutrients

As fermentation proceeds and yeast continue to propagate, they pass along a certain amount of cellular material to future generations. In juice/must without proper yeast rehydration, a gradual reduction in cell membrane thickness and decreasing amounts of nutrient reserve transfer from generation to generation is common as fermentation continues. This had led many producers to include the use of yeast rehydration nutrients to help make their yeast ‘happy’ during the rehydration process, and lead to a healthy yeast population, essential to successful fermentation.

There are several proprietary yeast rehydration nutrients available today, including Dynastart, GoFerm, and PreFerm. They are created from autolyzed yeast cells, and provide many essential micronutrients (including membrane lipids and sterols) and vitamins (including biotin, niacin, and thiamine) that are readily absorbed by active yeast cells. Providing these during the rehydration process reactivates the yeast’s internal metabolism quicker and leads to a substantial increase in cell volume; the original structures of the yeast’s plasmatic membrane are modified, leading to better viability, increased membrane fluidity, increased resistance to ethanol (essential towards the end of ferment), increased resistance to osmotic shock due to high sugar concentration (essential at inoculation), and increased aroma production (essential for good tasting wine!). Yeasts prepared with yeast rehydration nutrients also maintain a steadier metabolic rate throughout fermentation. Less stress also means far less volatile acidity formation and negative sulfur-containing compounds (hydrogen sulfide, disulfides).

The use of yeast rehydration nutrients is recommended at a 5:6 ratio with yeast (5 parts yeast to 6 parts rehydration nutrients, usually 250 ppm yeast with 300 ppm nutrient). I tend to use the recommended rate only when I know that strenuous fermentation conditions are inevitable (high brix levels, low fermentation temperature, low turbidity juice, historically deficient juice, etc.) or during yeast starter culture propagation. For normal fermentation conditions, I tend to use a 1:1 ratio (usually 200 ppm yeast and 200 ppm yeast rehydration nutrients).Winemakers also need to be wary of legal dosages of particular ingredients (i.e. thiamine) when using yeast rehydration nutrients in conjunction with other fermentation nutrients.

Please see here for yeast rehydration preparation.

Mike Horton is a winemaker with a passion for surfing. Correction… he is a surfer with a passion for winemaking. Yeast Rehydration Nutrients was originally posted on his blog: the drifting winemaker.

 

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Wine yeast nutrients 101

Various parts of dead yeasts can be used as a source of nutrition / alcohol tolerance for live yeast cells during fermentation. Sometimes they are used in combination with inorganic nitrogen such as DAP and sometimes they are used on their own. Here is a short explanation of the different types:

Inactivated yeast – the whole yeast cell has been killed by heat. It contains the cell wall, the cell membrane and the whole inside of the yeast. Inactivated yeasts are a source of vitamins, minerals and to a lesser extend amino acids. As the alcohol content of the must increases during fermentation the dead yeasts’ cell membranes become more and more “leaky” and more of the inside goodies of the dead yeasts leak out to the must where the live yeasts can take it up. This does not happen to live yeasts since live ones can regenerate their cell membranes. They can keep it together so to speak. Inactivated yeasts are found in products such as Fermaid K and E (Lallemand) and Maxaferm and Nutrivin (Oenobrands).

Yeast autolysate – the whole yeast cell is killed and then exposed to lytic enzymes at 45°C for a certain time period. The result is that the cell wall, that contains glucans, is partially degraded and the cell membrane and the “soluble inside” of the yeast are more exposed, and therefore more available, to the hungry fermenting yeasts (cannibals) lurking around for a bite. Commercial examples are Natuferm (Oenobrands), Go-FermProtect (Lallemand) and Dynastart (Laffort). These products are usually added separately from inorganic nitrogen. They are applied for specific purposes and they are more effective than normal inactivated yeast. Apart from the normal role of nutrition they also do the following: Natuferm = aroma enhancement, especially esters; Go-Ferm Protect = source of sterols and Dynastart = aroma enhancement, especially thiols.

Yeast cell walls /hulls / ghosts – this is the insoluble yeast cell wall fraction of yeast autolysate after centrifugation. Depending on the washing process used during the manufacturing of yeast hulls, they may or may not contain parts of the cell membrane. Commercial examples are Extraferm (Oenobrands) and Springcell (Bio-Springer). Technically they are not nutrients, they detoxify the must from medium chain fatty acids produced by sluggish yeasts.

Yeast extract – the supernatant of yeast autolysate or in plain English: the soluble insides of yeast cells once the insoluble cell walls and cell membranes have been removed. This is found in Superfood (Vinotec).

Specific yeast fractions – e.g. mannoproteins. Mannoproteins are a specific cell wall constituent and production thereof requires further processing of yeast cell walls. Technically they are not nutrients either. They assist with tartrate stabilisation and mouthfeel. Commercial examples are Claristar (Oenobrands) and Mannostab (Laffort).

For more detailed info on the topic go the technical article with the same title.

Karien O’Kennedy is the Online Communications Manager of Oenobrands and knows the odd thing or two about winemaking and fermentation.

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Winemaking in the Rhineland-Pfalz: Part 2

During my recent harvest stint in Germany, my host, Christoph Hammel uttered many memorable (and some that I am not allowed to mention here) pearls of wisdom. He told me about a meeting where some of the biggest names in German winemaking and professors associated with the wine industry were present. A very well know professor publically stated that his belief system does not have any room for the theory that yeasts impart any aroma to a wine fermentation. At this, Christoph got up and glibly replied: “My dear sir, it is not a question of belief. It is a question of knowledge.” The subsequent pandemonium that ensued was apparently quite noteworthy (hence the photo above).

Christoph is a big believer in using technology, specifically technology that can be used to make wine, and wine processing, better. Even more specifically, he is a big believer in additions.  He always said to me that he makes wine that people want to drink and if this can be achieved with the addition of enzymes and other winemaking tools, so be it. Every addition that he does is done for a reason. One thing can be said with certainty and that is that Christoph believes in the “interventionist” approach to winemaking. A lot of winemakers like to claim that their wine is made “naturally” and with the least possible human intervention, but Christoph is at the complete opposite of the spectrum. He has some pretty far out and amazing ideas and some might even call him a renegade or a cowboy after hearing about his yeast mixing and addition regimes!

As far as the additions are concerned, Optiwhite (Lallemand) is one of his stalwarts. This is usually added at the beginning of fermentation. β-glucanase and β-glycosidase enzymes  are added at the end of fermentation (at about 0°Brix). Depending on the structure and quality of a specific wine, ascorbic acid is also added right at the end of fermentation. DAP is added at three stages and is sometimes even added in divided dosages during the day, depending on the fermentation bouquet. In addition to DAP addition, thiamine is added to all musts. This is done simultaneously with sugar addition. It is well known that fungal infection on grapes depletes thiamine and it is therefore an excellent prophylactic measurement against stuck, sluggish or smelly ferments. For each addition, a cost to benefit decision is made. For instance, light and easy drinking wines will not get all the bells and whistles. The more expensive wines will get a full range of stuff added.

If Christoph was not such an excellent winemaker, I would have said that he missed his true calling in life: A chef! A chef who is forever mixing, adding and tasting, mixing, adding and tasting…

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The power of yeast hulls!

In the aftermath of the Southern hemisphere harvest, some poor unfortunates are still struggling with stuck fermentations.  In most cases when looking at the facts one can pinpoint why the stuck occurred, but on the odd occasion the reason is not very clear. I had a situation last week where the winemaker, who also happens to be a consultant to other winemakers, had one of these un-explainable stucks. (I think I’ve just created a new word.) He did everything by the book, made all the right choices, grapes were of good quality, etc. Naturally, the first instinct of winemakers when they see the RS remaining the same for more than a week is to consider re-inoculation. Now, this is where the good news comes in. It seems that there is a miracle product, called yeast hulls, which can potentially save you this costly, time consuming, hair pulling, teeth gnashing, and no guarantee that it will work experience.

Yeast companies recommend the use of pure yeast hulls as part of a re-inoculation protocol. The science behind it is that the yeast that got stuck was under stress to survive and as a result produced medium chain fatty acids. These medium chain fatty acids are toxic to the fermenting yeast as well as to the new yeast used for re-inoculation, as well as to MLF bacteria. So one has to “detoxify” the must first before inoculating with new yeast.  The recommended contact time with yeast hulls before starting the re-inoculation process is 48 hours.

However, I have seen on more than one occasion that the addition of yeast hulls can lift the inhibition on the stuck yeast, with fermentation starting again and completing without the need to re-inoculate. Over time I have come to identify a possible scenario where such a phenomenon is possible. It seems that if the total yeast count is more than one million cells per ml and the yeast viability is 30% or more, then there is a chance that the fermentation might pull through. Depending on the other existing must conditions it might not be possible for the fermentation to go bone dry, but it might get the wine into a “blendable” (another new word? poor English?) condition.

In the particular case I dealt with last week the wine had an RS of 12 g/l. The wine was stuck at that sugar for over a week. The winemaker added Bio-Springer yeast hulls at 40 g/hl and the residual sugar went down to 3 g/l in less than a week.  His yeast cell count and viability were over one million cells per ml and 30% respectively.  In other cases that I am aware off where yeast hulls allowed fermentation to complete, the product Extraferm from Oenobrands was used at a dosage of 50 g/hl.

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Yeast cell walls versus inactivated yeasts…

Yeast cell walls are also known as yeast hulls or yeast ghosts. Many sales reps sell yeast nutrients that they claim contain yeast cell walls when in fact they contain the whole yeast that has been inactivated. So what is the difference in application between cell walls and the whole inactivated yeast?
 
First a basic lesson in yeast cell morphology: yeast consists of a cell wall, on the inside of that you get the cell membrane and on the inside of that, well… the rest of the yeast. The cell wall consists mainly of glucans and mannoproteins (so-called polysaccharides) and the cell membrane consists of lipids (the fancy scientific name for fat). The lipids are made up of sterols and long chain fatty acids.
 
Both cell walls used on their own, and inactivated yeast containing the cell wall, membrane and yeast insides, stimulate fermentation. They do this in different ways though. Inactivated yeasts serve as a yeast nutrient in that they can be a source of vitamins and minerals. They can also be a source of sterols and long chain fatty acids. Live yeasts are little cannibals feasting on their dead counterparts when the going gets tough, i.e. the alcohol gets higher. To survive they need to strengthen their cell membranes and to do this they need more sterols and long chain fatty acids. They produce the latter in the presence of oxygen only. During fermentation oxygen is limited so they go for option B and that is to obtain these components from their dead mates. Reminds me of the movie Alive about the soccer team whose plane crash landed in the Andes Mountains. Yummy… Inactivated yeast insides also contain compounds such as amino acids and nucleotides that can “leak” out into the must and serve as a nutritious bite to the live cells.
 
Yeast cell walls are not a source of nutrients. They detoxify the must by removing medium chain fatty acids from the must, making the environment nicer and easier to ferment in for the live cells. Okay…long chain, medium chain, what’s the story? Live cells need to have an intact cell membrane containing long chain fatty acids to survive increasing alcohol toxicity. As alcohol levels become higher during fermentation, the live yeast starts to produce more fatty acids; however this process requires oxygen, which is limited or completely absent. The manufacturing of the fatty acid gets interrupted and the result is a much shorter chain that cannot be used in the cell membrane. These chains either stay associated with the yeast cell or get secreted into the medium. They physically block sugar uptake. For some reason they bind to yeast cell walls added to the must and the inhibition gets lifted.  
 
The commercial production of yeast cell walls is a much more complicated and expensive process than that of producing inactivated yeast. It is therefore usually a more expensive product. Depending on your specific fermentation conditions, you will use one or the other.
 
For a more comprehensive and slightly more serious explanation of the different types of yeast nutrients read the article, Wine yeast nutrients 101.
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