02 Mar Selecting and producing your own yeast directly in the cellar – you can do it!
On the one hand is the desire to enhance the microbial biodiversity of musts linked to the vineyard and the winery, and on the other the need to manage fermentation in a safe and controlled manner.
How can these two factors be reconciled?
Researchers from the University of Florence and the Academic Spin Off of Food Microteam combined their experience and skills with Parsec’s know-how and professionalism to develop MyYeast, a process for selecting, preserving, multiplying and producing yeast directly in the cellar, thanks to Cellar Mate Plus MyYeast and MyYeast Reactor technology.
The process and initial prototype were developed a few years ago, as part of the VICAStart project, which involved the winery VI.C.A.S. (Viticoltori delle Colline Arno e Sieve), the University of Florence’s GESAAF Department with the research team of Professor Lisa Granchi from the Food and Microbiological Sciences and Technologies division, along with Professor Alessandro Parenti from the Agricultural, Forestry and Biosystems Engineering division, Food MicroTeam Srl and Parsec Srl as technical partners.
Autochthonous yeasts in the cellar
Giacomo Buscioni, co-founder and scientific head of the wine division of Food Micro Team and one of Italy’s leading experts in the microbial ecology of alcoholic fermentations, explains what cellar yeasts are and how they contribute to the winery’s style as well as to the quality and distinctiveness of its wines.
“In our studies on the ecology of Saccharomyces cerevisiae populations, over the years and in practically all wineries where we have studied spontaneous fermentations, we have always verified the presence of dominant strains – sometimes just one and occasionally two or three and less frequently more – that manage to ‘dominate’ the fermentation in a vintage. Other strains are also occasionally present with isolation frequencies of 1
to 2%, hence why they are defined as being a ’minority’ and able to characterise fermentations in a much less significant manner than the dominant ones. What’s more, by repeating these observations over several years, we have found that some of these ‘dominant’ strains can recur in several successive vintages, which is why they should be considered as recurrent and thus indigenous to the winery.”
There are therefore a number of yeasts that are characteristic of wineries and estates and which – year after year – contribute to the typicality and style of the wines and thus able to be defined as autochthonous strains of the winery or estate. But where do they come from?
“Saccharomyces cerevisiae is present on grapes with small but not entirely absent populations and, in fact, some research groups are looking for them specifically on the grapes. Instead, we have chosen to select them directly from the musts since the isolation during fermentation will enable us to select the strains – regardless of their origin – that are capable of dominating the fermentation and establishing themselves as recurrent in a cellar’s
wines. Indeed, it is the wine fermentation process itself that selects the most suitable strains for the style of wine to be created – unlike the process of testing the technological capacities of the populations on the bunch, not having yet been subjected to the selective pressure of the cellar environment and winemaking practices.”
Hence, the first step taken by the Food Micro Team researchers is to isolate the strains present in a spontaneous fermentation, to then be genetically characterised before testing their metabolic and technological capabilities.
“If a cellar wants to take this route, it must dedicate at least a few tanks, of a size comparable to those normally used, to carry out spontaneous fermentation, managing all aspects of the vinification (nitrogen nutrition, oxygenation, temperature, handling operations and so on) in a way that is completely identical to the protocols normally adopted within the cellar. From these tanks, indigenous strains are isolated before undergoing the selection process. One of the advantages of making one’s own selection is that the cellar can identify the strains with the best adaptation, not only
to the characteristics of its musts but also to the winemaking techniques applied. For example, if the musts of the cellar in question are generally low in nitrogen, strains with low needs will be selected. It is not so much the variety of the grape (which the yeast cannot determine) but rather the chemical and physical characteristics of the must that influence its metabolism, along with the type of vinification (temperature or other techniques),” continues the Florentine researcher.
The dominant strains thus isolated during fermentation are then genetically characterised to exclude those corresponding to the most common commercial strains that may be present in the environment. The native strains of a cellar to have dominated the spontaneous fermentations, resulting in quality products, proceed with the next step of assessing the technological characteristics and sought-after organoleptic style.
Verification of the performance of the selected strain(s) in comparison with the commercial strains utilised in the cellar takes place during the following spring, on frozen must stored by the cellar, with a series of small-scale tests carried out in the experimental cellar of Cantina Tuscania, as a partner of the MyYeast® service.
“La degustazione in questa fase è fondamentale ed è il “Tasting at this stage is fundamental and is the point in which the producer and winemaker must say whether they like the new strains selected and above all, whether they reflect the style sought after, being specific and unique for the wines of their cellar. From the next harvest, we can continue with the
ecological study, seeking other strains or even starting to use the positive strain or strains, either individually or in a mix so as to mimic what is a spontaneous fermentation, with the possibility of better adapting to any eventual differences in the starting musts or fermentation conditions adopted by the winery,” continues Buscioni.
But the work and experimentation within the cellar does not end there. As happens every time new techniques are introduced (and even simply when there is a change in the commercial yeast strain utilised), one or more years of trials will be needed to understand the best conditions for use and the most suitable protocols for ensuring the new strains work at their best.
“It is necessary to optimise nitrogen nutrition, temperatures and, of course, the oxygen which, in managing both red and white grape fermentations, must be considered as a nutrient for the yeast.
The yeast not only multiplies further but, being in a more favourable physiological state, also expresses itself differently in the production of secondary metabolites, such as aromatic compounds.”
The yeasts selected by a company are for its exclusive use. They are deposited in the Food Micro Bank of strains to guarantee their storage at -80° C (-112° F) for the preservation and maintenance of genetic and microbiological purity. It is from there that the inoculum destined for the production of yeast paste for each harvest will be extracted.
Yeast production directly in the cellar
The multiplication of the biomass in the best physiological conditions for a regular and optimal start and continuation of the fermentation is entrusted to Cellar Mate Plus MyYeast, the reactor system developed by Parsec to produce the yeast directly within the cellar, with characteristics of purity and vitality able to meet those required by the International Organisation of Vine and Wine. The yeast can even be reduced to a paste using an additional semi-automatic device.
But what characteristics must the yeast present at the time of inoculation?
“The first thing is the number: in order to dominate over the populations already present, the cells of the introduced strain must all be numerically prevalent,
thus be introduced with a population of more than 1–2 million cells per millilitre of must,” explains Buscioni.
Compared to the production of active dry yeast, the production of liquid or paste yeast is simpler and less costly. In addition to allowing any strain to be multiplied – regardless of its sensitivity to drying (since some are not suited to this process) – it does not subject the cells to unnecessary stress, given that the yeast does not have to be transported or stored for extensive periods, as is the case with commercially-available dry yeast.
For small production runs of cellar yeast, which can be stored in refrigerated conditions for at least two months after production, yeast in dough form is undoubtedly the most viable solution.
“In an installation for the production of an inoculum,” adds Giuseppe Floridia, CEO of Parsec, who personally supervised the design and construction of the system, “the difficulty lies not in making the yeasts multiply – it is not that hard to have cells multiply, let’s just say that if they multiply, they are doing their job – but lies in managing this multiplication appropriately and competently. In developing the yeast production and preparation system, which went on to become the CellarMate Plus MyYeast, the most advanced techniques and scientific knowledge were applied to create a viable and efficient inoculum, with the invaluable support of the specialists of the Food Micro Team.
The processes were optimised and all necessary operational solutions were identified so that the CellarMate Plus MyYeast device could be used in the cellar with ease. To provide an example, which might seem like a minor detail but which turned out to be rather fundamental, we made sure that the production cycle times coincided with the schedules of the cellar workers. Activated in the morning, the process ends on the same day, with the collection of the biomass before the end of the work shift. And just like this factor, many other details turned out to be really important, such as the absence of heating elements immersed in the medium or the method chosen for stirring the mass.”
Particular attention was paid to perfecting the recipe for the multiplication medium, to the dosage of nutrients, oxygen and sugars, to the correct homogenisation of the mass and – of course – the washing cycles to prevent the proliferation of contaminating yeasts or bacteria.
“You cannot think of producing microbial cultures without thinking very carefully about cleanliness. Indeed, within the machine built by Parsec, all surfaces are shiny and can be perfectly sanitised, whilst there are no moving parts such as paddles that are difficult to clean. The washing cycles are automatic and extremely important as they allow everything to be cleaned and sanitised after each use, so that even the smallest contamination cannot proliferate and become a major problem in subsequent cycles”, explains Giacomo Buscioni. “The best conditions for the yeast to multiply are those in which the cells can breathe. Hence, special attention was paid to the dosage and management of oxygen.
Yet Saccharomyces cerevisiae is a positive Crabtree organism, meaning that it belongs to the group of microorganisms in which the respiratory metabolism is inhibited by high concentrations of glucose. Consequently, the addition of sugars is also carried out with a special automatic dosage at the times and in the doses required for each step of the process – as is the case for the addition of nitrogenous nutrients, sterols, vitamins and fatty acids, all products for oenological use that are readily available and manageable in the storeroom of a wine cellar.”
Using CellarMate Plus MyYeast in the cellar
How is the reactor used to produce yeast? Giuseppe Floridia describes the process and possibilities of using the system.
“To begin with, the starting medium is prepared and the yeast is added – an operation that we have chosen to do manually in order to avoid dosing or automatisms that could present a source of pollution. At this point, the machine handles the subsequent operations and additions of sugars and nutrients in the necessary ways and at the appropriate times, depending on the objective to be achieved, with a standard process or with a recipe optimised for each individual strain (with the initial set-up operation carried out with the support of Parsec and Food Micro Team specialists). Once the system is up and running, the process is very simple and repetitive. The yeast can be produced in the weeks leading up to the harvest and stored in the refrigerator (if in paste form) or even on a daily basis to then be use on the day’s harvested grapes. One of the positive aspects of making your own yeast is that you can create programmes that can be adapted to the logistics, organisation of the harvest and the cellar’s grape production estimates.
The machine is extremely versatile and can be used not only in the production of inoculum but also in the preparation of the ‘pied de cuve’ for acclimatising the yeast to the conditions of fermentation of the musts or re-fermentation in the production of sparkling wines, in any case bearing in mind that the transition between the two processes is extremely delicate and must always be preceded by an extremely careful sanitisation and disinfection of all equipment. The best solutions for preventing undesirable pollution in the multiplication of the inoculum involve the use of two systems – one dedicated to the multiplication of the inoculum paste and one to the preparation of the pied de cuve – or alternatively, to temporally separate the two processes by producing the yeast for all phases of the harvest and then using CellarMate for the pied de cuve preparation that is perfectly adapted to the conditions of the wine.”
CellarMate Plus MyYeast and the MyYeast Reactor are part of Parsec’s CellarMate range.
The specialists at Parsec, as an international leader in the management of oenological processes, have combined their engineering and oenological skills with their knowledge of the physiology and biology of yeast to meet all requirements for the rehydration, multiplication and acclimatisation of yeast with specific or multifunctional models, not only for fermentation but also for the refermentation of musts and wines.