TOTM, 6/07: Fermentation

[jeff]

This month we'll continue Bourbon Making 101 with a discussion of fermentation. Discussions should include a description of fermentation, different yeast strains available, propagation of "ancient" strains vs. using commercially available yeasts, open vs. closed fermenting vats and who uses what, attenuation, back-set, or any other topic related to yeasts, on their quest to turn sugar into liquid gold!

Sound off

[BourbonJoe]

I noted from many distillery tours that most distillers start with a certain gallonage (%) of backset to start a new batch. Four Roses takes a more scientific approach and bases the amount of backset on pH. Interesting.
Joe

[barturtle]

Okay open v. closed:

Here's what I can recall from tours:

Open:
Makers (though not having gotten in to see the unoffical stainless fermenters, they could be different)
Buffalo Trace
Wild Turkey

Closed:
Jim Beam

I can't seem to recall What Four Roses and Woodford use...must be time to revisit them. Any one know them or Heaven Hill or Brown Forman or Barton?

I must say I like the idea of some "wild" yeast being able to get in there to add some flavor depth, but then again in some ways consistancy is key.

[Gillman]

Open fermenters, especially where fermentation is done at ambient temperatures as in Kentucky I understand, often would produce an estery beer, which lends a fruity taste that is noticeable in many new distillates and can show in the final aged product. Open fermenters are used classically with top fermentation yeasts (but are used with bottom yeasts too, e.g., as originally at Pilsen for its Urquel) and I think this kind of yeast still is the norm in the bourbon industry (whether jug or cultured).

E.g., Woodford and its related whiskeys seem to have a cherry-like taste which may be a product of this yeast character. I find something similar in, say, Weller 107. Some whiskeys seem to stress a peach or apricot character.

Closed fermenters would lessen the chance of estery effects although it depends too on the temperature of the fermentation. I understand that even top yeasts tend to behave like bottom ones in closed fermentation vessels, especially the tall inverted cone-type units. This would result in a more neutral character from a yeast standpoint.

Another point about liquor fermentation: you want a high degree of attenuation, you don't want residual sugars to lend taste because that represents (in distilling as opposed to brewing beverage beer) wasted alcohol.

Gary

[Edward_call_me_Ed]

Can I ask a dumb question?

How can they use open top fermenters without ending up with vinegar at least some of the time?

Ed

[Gillman]

Well, the yeasts are stable enough, and the fermentation controlled enough (including not over-prolonging it), not to have these accidents occur (although probably they do occasionally, as most brewers can state I think). The interaction though of some wild yeast with the yeast working in the brew may give some house character to some beers, you see this with a number of Belgian ales which have a sourish or acid taste. In balance though, that can be a plus.

Gary

[bobbyc]

Barton = Closed
Woodford = Open

Don't know the rest

[Gillman]

It's interesting because of the distilleries identified as using closed fermenters, their products to my taste have the least estery taste in the industry. Barton's whiskeys seem very clean in general, and so are Beam's, even Knob Creek (not to mention Booker's and Baker's) doesn't really have an estery component. True, Beam Black sometimes achieves an estery quality but I find this is the exception.

The plants using open fermenters however all seem to tend in the opposite direction: OF and WR are notably fruity, so is Rare Breed and many WT bottlings (not all, but that probably results intentionally from mingling to achieve certain profiles), yet Maker's seems (I admit) not to be (and I am assuming the current stock was all made before the sale). Probably the specific yeast used despite the open fermentation imparts little estery character or maybe they ferment at a lower temperature than the others who use open fermenters.

I think the type of yeast (even amongst the top yeast group) and especially fermentation temperature has the greatest say, yet still with little other data it is interesting that most of the open fermenter distillers produce relatively fruity whiskeys. I wonder what Trace does, I would think they must use open fermenters but possibly not, or maybe they use both types?

Gary

[boone]

We call them "mash tubs". Heaven Hill's is closed.

I took these pictures at Maker's Mark. Open mash tubs and view of how they monitor and control the work area in the distillery.

The PLC is the heartbeat in today's distilling industry. The "old distillery-DSP #31" had very little "new technology". Craig told me that they spent a lot of time "redoing" Bernheim. The entire process was controlled by PLC. They have modified Bernheim it so that certain elements are "turn key" or "human hand" operation so to speak.

[Gillman]

Bettye Jo, is the fermentation stage done in a different vessel or do they mash in and add yeast to the one tub?

Gary