Sourmash and yeast strains

[Flyfish]

I went to the 4R website to print out the formulae for their various barrel strength bourbons. Yeast strains play such a critical role in theirfinal products that a Cowdery kinda question occured to me: In the sourmash method, consistency is provided by backsetting some of existing mash into the next vat--just the way sourdough bread is self perpetuating. Even so, master distillers and yeast makers (their old title) maintain a library of jug or dry yeast. Is that yeast kept for "insurance" against the loss of a key component or is yeast also added to the sourmash? Why isn't the sourmash sufficient on its own?

[Gillman]

Sourmash in the old days meant different things. At one time, yeast from a fermented whiskey mash sometimes would be reserved for addition to the next ferment, and that is closest to the bread sourdough way of baking. However, as finally worked out in Kentucky and elsewhere in America for whiskey-making, backset (or set-back or slops) meant, not live yeast or yeasty (fermenting) mash, but the spent "beer" in the still, the lightly acidic water and other elements left after distilling out a quantity of fermented corn-based mash, or rye-based mash.

The pH lowers in the mash when backet is added to it, which helps to produce a more regular and consistent fermentation. You can add food-grade acids today to achieve a similar result.

So it has nothing really to do, today, with sourdough bread-making, but again at one time the analogy was relevant.

As you said, yeast cultures are important to flavor and there are other factors, e.g. you want the yeast to produce the right amount of alcohol, not too little, not too much, so the right congeners (co-products of fermentation such as acids, aldehydes, higher alcohols and esters) emerge which in time will assist to give the right flavour to the spirit.

Gary

[p_elliott]

I believe the yeast is dead in the back set. Yeast is added to the fermentting vat at some time during the filling. Distilleries keep samples of their yeast in different locations around the world so they can not all be killed at once I understand. Did this answer all your questions or did I not understand the question?

[Gillman]

I agree with Paul and also, or what is saying the same thing, if you simply scooped yeast and kept that for the next ferment, ultimately it would go bad by picking up foreign influences from airborne wild yeast and from various bacteria. The distilleries keep a pure culture so they can regularly culture up the amount they need for a ferment, and they know that way the yeast will keep its original characteristics which affect flavor and other performance criteria. It is the same for breweries.

Today some distilleries purchase a dried distillers yeast in some cases again made to their specifications. Dried yeast is, I have heard, very reliable if of good quality.

Gary

[Rutherford]

It's also worth noting that distilleries take breaks for maintenance, and almost nobody distills through the summer. Yeast needs to be kept to re-start after shutdowns.

[Ejmharris]

I went to the 4R website to print out the formulae for their various barrel strength bourbons. Yeast strains play such a critical role in theirfinal products that a Cowdery kinda question occured to me: In the sourmash method, consistency is provided by backsetting some of existing mash into the next vat--just the way sourdough bread is self perpetuating. Even so, master distillers and yeast makers (their old title) maintain a library of jug or dry yeast. Is that yeast kept for "insurance" against the loss of a key component or is yeast also added to the sourmash? Why isn't the sourmash sufficient on its own?

This made me think of another question regarding 4R's specifically and using backset. When they ferment a specific mashbill, obsk for example, do they use an OBSK backset? Seems like they would need a lot of extra storage for each of the mashbills.

[p_elliott]

This made me think of another question regarding 4R's specifically and using backset. When they ferment a specific mashbill, obsk for example, do they use an OBSK backset? Seems like they would need a lot of extra storage for each of the mashbills.

I don't think so like I said the yeast is dead in back set. But I could be wrong here.

[Gillman]

Not sure about Four Roses, but I know some distilleries starting up after a seasonal break just fetch backset from another distillery - saves running a sweet mash and (I infer) risking altering the process and taste too much. A bit of "foreign" backset at the beginning can't have much impact on all the throughput through a full season and even less factoring aging and mingling, etc.

Gary

[sutton]

I don't think so like I said the yeast is dead in back set. But I could be wrong here.

I think you're correct if the backset is the remains after the first distillation. Yeast are pretty much toast over 110 deg. F, and the first distillation is going well above that.

I imagine the only purpose of the backset is to drop the pH of the next fermentation as Gary said, to establish a healthy environment for the yeast that they'll ultimately innoculate with - and I'd imagine the backset is fairly sterile so you aren't going to introduce any microorganisms that might spoil the next batch. Getting the pH right ensure the yeast will do their job efficiently and without generating off-flavors (as a result of being in a less than optimal environment).

Of course, I'm taking a bit of an educated guess here from my own home ferments (beer/wine) ...

[tmckenzie]

one major function you get from using backset is it is a yeast nutrient. Makes the yeast have something besides sugar to eat. If you do not use this, you have got to add nutrients to the mash. Which most micros do along with adding acid. There is no live yeast in it. dry yeast will work good, we however just installed a yeast tank last week and will be growing yeast from now on.