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?

[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.

[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.

[Gillman]

I was reading up on this again and it appears many artisan distillers 1800's) added both backset and then actual fermentation lees to the the next mash, both to save the amount of fresh yeast needed for the next ferment and to improve flavor. You get lactic acid development which (as in some brewing) increases the complexity of the final spirit whether aged or white. One source said using only backset for the next mash was half of the original sourmashing process, i.e., that continued use of lees resulted in the best taste.

Reading all these old techniques, there is no surprise really that modern bourbon seems in general lighter and thinner than it was even in the 1970's.

Gary

[bad_scientist]

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.

So the yeast eat other yeast? Does this happen when they're stressed, as well?

[tmckenzie]

the yeast sells will attch themselves to dead yeast cells, and the cells have burst due to heat. Releasing all of the nutrients they consumed during fermentation. Winemakers will use yeastex, which is dead yeast cells if yeast get stressed. You know they are stressed if they start producing sulfur. Which you can smell.

[bad_scientist]

the yeast sells will attch themselves to dead yeast cells, and the cells have burst due to heat. Releasing all of the nutrients they consumed during fermentation. Winemakers will use yeastex, which is dead yeast cells if yeast get stressed. You know they are stressed if they start producing sulfur. Which you can smell.

Sorry to keep this going, but I have read the hypothesis that the butterscotch flavor common to dusties came from stressed yeast. Do you have experience with that sort of flavor profile?

[sutton]

Sorry to keep this going, but I have read the hypothesis that the butterscotch flavor common to dusties came from stressed yeast. Do you have experience with that sort of flavor profile?

You can get diacetyl (buttery aroma and flavor) as a by-product from yeast during fermentation under certain conditions - that is probably where it comes from. It is noticeable even at very low concentrations, and distillation would likely further concentrate any that was there.

[SmoothAmbler]

You can get butterscotch aromas much more so from small barrels too. Or at least we do. We don't sour mash, but we are playing around with doing some sour mash in the future.

I know some large distilleries that use a sweet mash to start after a shut down and then go back to the sour mash once the have stillage. Some also add some heads into the fermenter. Yeast seem to like low levels of ethanol.

[tmckenzie]

I feel like the type of stress that causes buttscoth comes from heat stress. Not lack of nutrition stress.

[Leopold]

Sorry to keep this going, but I have read the hypothesis that the butterscotch flavor common to dusties came from stressed yeast. Do you have experience with that sort of flavor profile?

It would certainly make sense that some older production methods could lead to more diacetyl in the finished whiskey. The stressing that you refer to in some yeast strains doesn't lead to the yeast's production of diacetyl; rather, stressed yeast can lose its ability to reduce diacetyl and 2,3 Pentandion (same flavor) that is produced during fermentation. Since diacetyl is reduced at roughly the same rate as other maturation compounds in beer, diacetyl reduction is measured (sometimes by simply tasting the beer) by brewers to gauge the total maturation of aging beer.

The bulk of diacetyl is formed during primary fermentation.... in other words, just after the yeast is added to the mash and is in the first throes of fermentation. Once this diacetyl has been formed and is in the mash, the very same yeast cells begin to reduce this diacetyl by converting it to butanediol. Butanediol is flavorless.

A few things affect this reduction process (I won't bore you by listing them all). You need healthy happy yeast (this is where your stress question comes in), high temperatures (there in spades in a distiller's fermentation), and a low pH.

What can happen is that the yeast for various reasons (poor yeast management, mutations, underpitching, etc.) loses its ability to reduce the sometimes massive amounts of diacetyl that the primary fermentation generates. Combine this with very, very tight shortened fermentation times (counted by distillers in hours rather than days) that don't allow the yeast enough time to reduce the diacetyl.... and boom, there's your diacetyl in your finished whiskey.

Nowadays, big distilleries by and large use dry yeast, which almost eliminates errors in yeast management protocols that distillers of the past faced because the dry yeast has the same fermentation performance every time. Mutation and a reduction in the ability to reduce diacetyl is pretty much impossible with dry yeast.

As a side note, I'm sure you've heard of krauesening in German brewing production. Krauesening is a method of adding fresh yeast cells and wort to beer that's already almost completely fermented (kraeusen is added at about 10% of the volume of the beer that's being krauesened). What this does is add active yeast cells to rather cold beer in a cold fermenter. These healthy active yeast cells mop up the last bits of diacetyl that were not reduced because traditional lager fermentations are so cold that diacetyl reduction is rarely complete if you just add yeast at the start and that's it.

Another way you can get elevated VDK's (diacetyl & 2,3 Pentandion) is from bacterial infection, but that's a whole 'nother story, and I would find it unlikely to be the cause of butterscotchy whiskey.

The final way is simply because of yeast strain selection. Some strains famously produce a mess of it.... a couple of British Ale strains are notorious for it.

(maybe more than you wanted to know)

[tmckenzie]

What he said. Thanks man, my brain hurts now.

[Gillman]

Indeed. It is probably one of Todd's explanations that explains the butterscotch quality of ND OT in the 70's and early 80's, but I guess we'll never know for sure.

What it does suggest too though (to me) is that "errors" can sometimes make fine whiskey...

Gary

[SmoothAmbler]

Not to kiss ass, but there's a reason many distillers, including me, call Todd Leopold for advice. That guy knows his stuff. It's pretty obvious from his post above.

[Leopold]

Appreciate the kind words, smooth ambler, but it sounds a lot fancier in print than it really is. Since I worked without a microscope as a brewer of lager beer for so many years, diacetyl reduction was one of the main guides I used for maturation.... in practice it was as complicated as "can I perceive butterscotch?" Which is about as simple a test as you get!

[bad_scientist]

Appreciate the kind words, smooth ambler, but it sounds a lot fancier in print than it really is. Since I worked without a microscope as a brewer of lager beer for so many years, diacetyl reduction was one of the main guides I used for maturation.... in practice it was as complicated as "can I perceive butterscotch?" Which is about as simple a test as you get!

Thanks for the superlative info! Most of my days are spent making and working with mutated mice, but in college it was all chemistry/pharmacology. Thanks for making me remember how much fun it can be!

[Leopold]

Indeed. It is probably one of Todd's explanations that explains the butterscotch quality of ND OT in the 70's and early 80's, but I guess we'll never know for sure.

What it does suggest too though (to me) is that "errors" can sometimes make fine whiskey...

Gary

[Bourbon Boiler]

Thanks to all of you, particularly the insiders for expanding this whiskey nerd's knowledge.