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| FREQUENTLY ASKED QUESTIONS |
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Frequently Asked Questions
1/ How to pitch dry yeast?
Dry yeast can be used as an inoculum directly into the fermentors, but we recommend carrying out a short rehydration at 35C for 30 minutes in sterile wort or water. The dry yeast will therefore be acclimatised and will begin to grow and to produce ethanol quicker.
2/ Can we propagate dry yeast?
When you try to propagate active dry yeast for a long time you reduce the efficiency of the yeast. The combination of temperature and ethanol concentrations (above 5%v/v) do increase the alcohol intolerance, resulting in cell mortality. Increasing the concentration of ethanol during propagation will initially be inhibitory and latterly lethal to the yeast.
However, the major risk in propagation is to propagate contaminants. When you try to propagate active dry yeast you can easily increase the levels of contamination because bacteria and wild yeast often grow quicker than Saccharomyces yeast.
We therefore recommend reducing the propagation time of dry yeast to a minimum (6 to 8 hours maximum).
3/ Can we recycle dry yeast?
The risks and the stress applied on yeast during recycling are similar to the one described in the propagation stage. In addition, there is the risk of development or unsuitable metabolites (such as lactic acid and acetic acid which strongly reduce the yeast efficiency) and the risk of genetic mutation and cellular ageing.
To maintain the best yeast efficiency we recommend that you avoid recycling.
4/ What quantity of dry yeast do I need in my process?
In direct pitching into the fermentation vessel the recommended pitching rate is between 25g and 50g per hectolitres, depending on the sugar concentration and the raw material you use. This will give a minimum of 5 million cells per ml when fermentation start.
When yeast is propagated over a few hours this required quantity has to be reduced. The model shown in the "directions for use" can help you to quantify the yeast requirement according to the propagation time and the propagation and fermentation tank sizes.
5/ What is the shelf life of dry yeast?
Dry yeast has a two years shelf life and can therefore be stored for some months without an extensive loss of viability if temperature and packaging are controlled. Dry yeast is therefore immediately available from the shelf and can be used as and when required by the distillery.
6/ Is Dry Alcohol Yeast similar to baking yeast?
No, Alcohol yeast has been specially selected in our R&D departments to provide the best fermentation performance in an anaerobic condition. It has been proven that these strains have a poor performance in bread production.
7/ Why are bacterial specifications so important?
Lactic and acetic bacteria can strongly affect the yeast performance. This can be explained by nutrient competition or direct killing. Fermentis' standards are the strictest in the market.
8/ How expensive is Dry alcohol yeast?
Cost of dry alcohol yeast is more expensive than Dry Baking yeast, because it is a specific strain that has been produced in the strictest bacterial conditions and with high specification. It has been proved that the use of speciality adapted yeast leads to a better yield and higher efficiency in the distillery. This easily compensates for the extra-cost.
The cost of dry yeast is nothing in comparison to the costly investments in microbiology and capital equipment that are needed to control the bacterial contamination and the physiological state of the yeast.
9/ Should the wort be supplemented with additional nutrients?
Nutrients such as Nitrogen, phosphor, minerals or vitamins are often present in limited quantity in the wort. The nutritional deficiencies encountered are mainly in Very High Gravity fermentation, but also it can affect performance of the yeast in normal gravity. Fermentis can recommend supplements after a precise analysis of the wort.
10/ How much ethanol is it possible to produce with Fermentis yeast?
The concentration of ethanol produced depends on the initial sugar concentration, the availability of the required nutrients and the ability of the yeast to resist to high alcohol concentration. In the Very High Gravity process Safethanol 3035 has proved that it is able to ferment a corn based substrate up to 21% v/v ethanol on laboratory scale and up to 18% ethanol in industrial production plant.
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