Sloppin' Back

Re-use of yeast is an old moonshiners trick also known as "sloppin' back". This refers to adding the mash that was strained out of the wash just prior to distilling, or the sludge left in the bottom of the fermentor, to the next batch of mash.

As Sam explains ..
    I did't strain mine so to speak. I pumped out beer from the barrel and left the grain. I used about half old and half new grain. NO YEAST. It is already there. I added water and the same amount of sugar as when I would start a fresh batch. Stir like crazy and you only have to wait for 3 days max for the cap to form and fall and you are ready for a good run. Like I mentioned, third time is the best as far as taste and quantity in my opinion.

This can be a good source of infection for the next batch, but if it goes well, it will help boost the yeast count heaps, act as a bit of a source of nutrients (though its still best to add more of the real stuff like ammonia), and should help buffer the pH a touch (dropping it a few 10 ths). The yeast that you're reusing by this technique are those that have already shown themselves to be quite happy in that type of mash, and are ready to go for the next lot.

It appears that the "Turbo" yeasts are only designed to be used once, and not reused. Ola Norrman writes ...
    Turbo Yeast (a mixture of yeast and nutrients) - shall never be reused. There are 2 main reasons for this:

    1. Yeast condition. During the manufacture of dried yeast, very high levels of phospholipids are accumulated within the plasma membrane because the yeast is grown aerobically (with oxygen). The yeast population which exists at the end of fermentation has depleted levels making yeast cells more sensitive during subsequent fermentations and fermentation more likely to stick.

      So the yeast produce and accumulates lipids during its growth in the yeast factory. Then, during anaerobic fermentation (without oxygen) in the wash, each new generation of yeast contains less and less lipids. Lipids are needed for alcohol tolerance which make this important to 14% Turbos and far more important to 18% Turbos. If to many generations have passed (because of reuse of yeast or to little yeast to start with) the yeast have low "lipid protection" and alcohol tolerance decrease.

      Dried yeast also contains typically 15% Trehalose which is a "protectant sugar". It gives the yeast cell internal strength and also is an excellent "start sugar" for the yeast to use at the start of fermentation. Cells at the end of fermentation will typically contain only 2 or 3% Trehalose. Trehalose protect against the shock when the yeast are mixed in the wash.

    2. Nutrient depletion. Not relevant for beer, partly relevant for wine but totally relevant for Turbo. So for Turbo, because the sugar offers no nutritional value, re-using the yeast a second time will result in a stuck.

      Turbos also contains pH-buffer to give the yeast perfect pH conditions. Nutrients not only work as nutrients, they also keep the production of volatiles down to a minimum. Nutrients are consumed by the yeast. Re-use of a Good Turbo yeast will also result in a lot more volatiles in the wash. pH-buffer will not work in the second batch. There are other ingredients making the CO2 leave faster, giving the yeast cells something to claim to and move around in the fermentation, assist clearing after fermentation etc. Those functions will also be spoiled as they are a part of the nutrients.

      Nutrient composition are the manufacturers secrets. One can not simply add some DAP (diammoniumphosphate) or similar and expect it to work the same. The first Turbo in the world was made in Sweden. They are sold under the name Prestige and are extremely good. At http://www.turbo-yeast.com/intro.html there is a lot of info about quality Turbos including a "recipe" telling how "Bad Turbos" are made.

      There is also info about yeast strains at: http://www.lallemand.com/ It is a bit surprising that they not have some never information here, only old basics.

      One could talk about genetic drift and bacterial risks too, but it is not so important.


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