2.3 Fermentation

Question 1

types of fermentation vessels

Answer 1

1. wood 2. steel (mild or stainless)

Question 2

Wood fermenters

Answer 2

typically pine (or birch), greater strength/ water tight (tyloses) vs oak and flvr contribution is irrelevant due to residence time, etc; traditional vessel type of batch distilleries, size is based on still capacity, but if only one pair of stills, it’s typical to have 2x capacity of wash still; flat-bottomed cylinder of vertical planks bound by metal hoops; wooden lid with removable hatch and electronically driven rotating blade (switcher) is fitted just below lid as a mechanical foam breaker (can’t use antifoam…); lid may carry spray ball for cleaning purposes, and also for sterilization if live steam is not used.

Question 3

Steel fermenters

Answer 3

mild –> typically epoxy lined, but very rare in modern distilleries. stainless –> typical practice, std for continuous distillation, dish-shaped, sloped, or conical, ; sanitary welds required- butt-ground, smooth…riveted=bad!; cooling jacket= ideal as cooling coils obstruct cleaning and can harbor MOs; one or more spray balls or a rotating jet would be expected as std cleaning (live steam for open-top or mild steel)

Question 4

yeast for use in distilling should meet the following requirements:

Answer 4

1. complete and rapid fermentation of sugars 2. good flavor production 3. tolerance of osmotic stress of the initial 16-20% sugar conc 4. ability to ferment to 8-10%+ ABV 5. no flocculence or chain formation (clumps fowling the heating coils of pot stills or trays of continuous stills 5. ability to grow well above 30C…fuel ethanol = 45-50C, but beverage = 35C as max 6. correct strain 7. free from bacteria and wild yeast contamination (or at reasonable levels, ie ADY ~100 cfu/g) 8. high vitality and viability

Question 5

1. Natural inoculum (rum and brandy yeast)

Answer 5

use of naturally occurring yeast flora or grape juice and molasses can be used either with or without use of supplementary cultured yeast. In either situation a low level of SO2 treatment is often used, insufficient to harm fermentative yeasts but hopefully inhibitory to bacteria and aerobic yeasts.

Question 6

5 sources of yeast for distilling

Answer 6

1. natural inoculum w/ or w/o used of cultured 2. yeast cake (28% DW) 3. cream yeast (18% DW) 4. ADY (95% DW) 5. Brewery yeast

Question 7

2. Yeast cake

Answer 7

28% DW, to be stored at 2-4C, and not lower b/c ice crystals would kill yeast puncturing cell membrane, and not higher because this would accelerate deterioration and encourage growth of bacteria and wild yeast contaminants present; should be used within 1 wk but can be stored for longer

Question 8

3. Cream yeast

Answer 8

18% DW, must be used as soon as possible, less than a week stored at 2-4C; stored in bulk (tote) which is pumped in a calculated amt

Question 9

4. ADY

Answer 9

95% DW, can be stored up to 12C (20C really…room T) for >1yr (3 yrs in ideal conditions); rehydration = best practices –> with or without sugar or nutrients, sterile water @~35C

Question 10

5. Brewery yeast

Answer 10

typically not used due to varying quality, and the potential for a mixed culture; cold storage required and used within 1-2 days

Question 11

Viability testing

Answer 11

MB= simplest –> redox dye, blue when in oxidative state and colorless when reduced…living cells either fail to take up the dye or if they do, reduce it to the colorless form. On death, cells rapidly become permeable to MB, and lacking metabolic activity, remain blue; although it does not distinguish between dead or alive (capable of reproduction) just with or without metabolic activity…at above 90%, this is not important, but below 90% this distinguish is important

Question 12

Vitality testing

Answer 12

more important vs viability…analogous to “fitness” in humans; simplest= acidification power –> active yeasts added to an unbuffeered 20% glucose solution will cause rapid decrease in pH by efflux of H+ asscociated with transport of sugar across membrane, to less than 4.0 within 20 min.; alternative version –> efflux of Mg ions is measured…more complex equipment is required vs a pH meter; rapid method= ATP content is measured by its stimulation of bioluminescence of the firefly extract used in detection of microbial contamination…$$

Question 13

Glucose vs fructose transportation

Answer 13

in most strains both are transported simultaneously, but in some there is preference for fructose.

Question 14

Cereal wort composition

Answer 14

Carbs= 90% of total solids–> 46% maltose, 15% maltotriose, 10% glucose, 10% maltotriose, 5% sucrose, 1% fructose and 13% maltopentaose and higher dextrins that will participate in SSF for further breakdown and consumption

Question 15

Cereal wort sequence of uptake into cell and metabolism

Answer 15

gluc (and fruc), then successively the increasingly larger saccharides

Question 16

whiskey vs rum vs brandy timeline for ferm

Answer 16

rum= typically high T and very quick; brandy = lower T and longer ferms in order to produce stonger estery flavors; whisky= middle, but depends

Question 17

falling pH in a pure culture ferm is related to?

Answer 17

the efflux of H= ions with sugar transport, or excretion of metabolites such as pyruvate or succinate as acids.; in molasses worts the pH changes are more pronounced because the N supply is mainly NH4+ with little or no buffering effect.

Question 18

In the yeast cell, stress is counter acted by… but can cause…

Answer 18

increased production of glycerol, glycogen, and trehalose, the latter two in the larger than normal vacuole, but under the microscope the most obvious effect of pitching into too strong of wort is plasmolysis (shrinkage) of the yeast cells,,,osmotic effects appear to be too strong for the cytomplasmic membrane to control; high external alc conc has equally drastiv effects, partly since alc can not escape and more remains within the cell, affecting E activity, and causing other damage. Loss of intracellular material causes plasmolysis and ultimately cell death.