Sweet Mash -vs- Sour Mash

[brendaj]

Gary,

I was wondering where the yeast for the successive mashes came from, ie. was it collected from previous ferments (before the boils) or was it made anew for each batch from a pure culture? I think Mike and you answered that, it either is propagated in jugs from previous brews

In a way, it's probably a little of both.
I baked sourdough bread for about a year. The original culture was given to me by a friend, and had to be 'fed' once a week to keep it alive. I would divide the culture, using half to bake bread (or flush down the toilet...we were living on a farm/septic system... ). I would 'feed' the other half with flour. It would show signs of fermentation, just like a mashtub.
What I learned, after a year of doing that, is how much I could change the taste of the bread, by what I 'fed' the yeast.
I'm sure the same thing applies here.
Bj

[Gillman]

Interesting. In beer fermentation, you would take yeast from a "first" fermenting mash (skim it off) and keep some in a jug for the next one, and so on. That was the traditional way but as mentioned earlier, the yeast would need to be revived/corrected periodically (today, by reference to a single cell yeast isolated in the lab) because it would alter its taste too much or lose power to ferment correctly otherwise. Your bread culture is truly separately made in that you obtained and fed it from sources separate from what was being fermented. In fresh bread, yeast acts on sugars in the loaf to make both CO2 (helps loaf to rise) and (some) alcohol which mostly lifts off into the air, ie. some residual remains in the bread, but just traces. But whatever propagated yeast is created in the bread itself (reproducing itself) stays only in the bread, which is why fresh sourdough and other yeast baking is intensely yeasty in taste. So, there are different ways to keep the yeast in the jug going too..

Gary

[Gillman]

The other thing this discussion raises in my mind is the effect of yeast on whiskey flavour. Many distillers insist on the importance of yeast in this sense. Lincoln Henderson does in the symposium in the current Malt magazine. Many other distillers have said similar. While beer brewrers know this to be true for beer, initially I was surprised that a mash heated at least to a temperature to make ethanol volatile could transmit that yeast taste to the condensing spirit. Yet, that it must do so seems unarguable. In the current Jim Beam whiskey range, I feel one may be able to detect a uniform yeast taste. It is a dry, lightly astringent, citric-like taste. It is reminiscent in particular of certain Belgian beers (e.g. Chimay, Orval) which are unfiltered. I understand Baker's, Booker's and Knob Creek use different mashbills. Yet, in a recent side-by-side tasting I felt I detected that signature flavour in all of them. It isn't dominant but is a discernible flavour element. Maybe this isn't the Beam yeast but something else I am noticing.. The 1960 decanter Beam brought to the Gazebo '03 did not have that taste at all, so either yeasts evolve over time, or something other than yeast explains it. If I was told Beam uses the same yeast for Baker, Booker's and Knob Creek, to me that's a further suggestion that what I am detecting is a yeast flavour. If the yeasts used in these three bourbons are different strains, that argues against my deduction..

Gary

[mickblueeyes]

There are some very important topics brought to light here. With regard to "Distillation killing the yeast"--good point, but the backset is taken prior to distillation, while still in beer form.

The variant role that yeast play in fermentation is interesting to say the least. Certainly in brewing, various substrains of Saccharomyces cervisiae (I don't know of any distillers that use Saccharomyces carlsberginsis) create different flavors, as their biochemical processes will vary slightly. This may create more of the interesting compounds left over in the new make spirit such as esters, acetyl aldehydes and heavier fusel oils. There is some interesting research going on right now as to how that affects flavor. Does the ethanol act as a solvent or catalyst for the breakdown of lignin into tannins and vanillins, or do the congeners left over from distillation degrade the intensely ligated cellulose structure.

As far as the yeast are concerned, the proprietary strain will have an effect on the taste of the beer, which will manifest itself in the distillate. There can be no question of that.

Fermenting and brewing require continuity in cultured yeast. This can be done two ways: commercially prepared cultures from the same lab each time, or reculturing (backset)

With regard to "souring" the mash, I am not sure of the definition of "sweet mash". I do know that several distilleries utilize Lactobacillus to assist with "souring' the mash, though I am uncertain of the purpose of this.

[cowdery]

but the backset is taken prior to distillation, while still in beer form.

Uh uh. The backset is "spent mash," i.e., post-distillation.

[mickblueeyes]

Cowdery, if backset is to be used, as purported, as a starter yeast culture, it would have to have viable yeast in it. 170 degrees F is high enough to break down proteins (ie protein denaturation) in all but the most steadfast organisms (E. coli, Pseudomonas Aeruginosa, etc.), rendering the yeast unusuable. So unless backset is used for some other purpose, which, frankly, I don't know, then it would have to be taken prior to distillation.

If there is a better explanation, please give it. I honestly just want to understand.

[cowdery]

The purpose of backset is to condition the new mash so that it is hospitable to the yeast organisms you want and hostile to yeasts and other microorganisms you don't want. It's not a source of live yeast. Backset prevents contamination of the mash by wild yeast and other common microorganisms. Yeast is added to the mash after the backset. Today, distillers use either a pure culture yeast or a jug yeast, which is made by capturing a strain they like from the air and propogating it in a special medium. Even pure culture yeasts are "mixed up" first in a medium that resembles the mash/backset but with some variations. Only after the yeast has started to vigorously do its thing in that medium is it added to the mash/backset in the fermenters.

[bobbyc]

So unless backset is used for some other purpose, which, frankly, I don't know,

Exactly

[mickblueeyes]

Thanks for the explanation Cowdery. As a microbiologist and brewer, I still fail to see how that creates a more hospitable environment. In brewing, I always keep dregs of the fermented wort for the next batch as a viable culture.

BobbyC, if your comment was intended as I think, you shouldn't have bothered. If not, no problem.

[bobbyc]

A portion of the spent mash was returned to the fermentation process initially for water content and heat. Along the way someone discovered that it also lowered the ph and hence the "sour mash" process.