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You know, that is a good point and I have wondered that myself. Many times. Never enough to actually look into it. So... let's do that, and let's pretend the yeast in a yeast bomb is like nutritional yeast?VLAGAVULVIN wrote: ↑Sun Oct 25, 2020 5:44 am P.S. The cooked yeast nitro bomb would easily contain some free form BCAAs, too. The point is: any significant qty. of them or not...
Well. The yeast cell has "eaten" some protein. What is the metabolite of this absorption?
The best way here is weak ferment / low starting gravity. The sooner stops = the better.Based on the general principles of metabolism on this planet, living yeast cells will follow the path of the least energy consumption.
There are a couple of factors here to think about.VLAGAVULVIN wrote: ↑Sun Oct 25, 2020 8:49 am By the way, I'm playing now with that Swiss Calculator (thanks to Stibnut again)... and still cannae make it out how the Scotts do get their esters and fatty acids. The first are killed by stripping, the rest - by spirit runs. Newly formed during the 2nd run reboiling? OK for some esters, but acids, like butyric, isovaleric and so forth? They cheat somehow, don't they?
Thanks for all your information about the Ehrlich pathway, zapata! I didn't know as much as i should about it - I just had a vague knowledge that some amino acids get broken down into fusels. This makes me wonder what the odor and taste of non-BCAA Ehrlich products are, and whether any of the ones with say nitrogen or sulfur side chains carry over into the distillate. I do know that 2-phenylethanol comes from phenylalanine and has a nice floral odor.zapata wrote: ↑Mon Oct 26, 2020 3:24 am On a purely practical level, we have many people over years (myself included) seeing good results from feeding yeast with yeast. We have commercial sources that use yeast for quite expensive yeast supplements. On a laboratory scale, YEPD (Yeast Extract Peptone Dextrose) is the go to media from researchers to yeast producers, and it's basically a fancy yeast bomb with corn sugar. Feeding yeast dead yeast is a thing, it's real, and it's has solid theoretical support and proven practical results.
You know, that is a good point and I have wondered that myself. Many times. Never enough to actually look into it. So... let's do that, and let's pretend the yeast in a yeast bomb is like nutritional yeast?VLAGAVULVIN wrote: ↑Sun Oct 25, 2020 5:44 am P.S. The cooked yeast nitro bomb would easily contain some free form BCAAs, too. The point is: any significant qty. of them or not...
Nutritional yeast has 8 grams of protein per 15 gram (1/4 cup) serving, so .53 mg protein / gram. Of the protein, in mg/g of protein it has:
Valine: 49 mg / g of protein 398 mg total in 15 grams (1/4 cup)
Isoleucine: 37 mg / g of protein 296 mg total in 15 grams (1/4 cup)
Leucine: 64 mg / g of protein 512 mg total in 15 grams (1/4 cup)
Phenylalanine 33 mg / g of protein 264 mg total in 15 grams (1/4 cup)
Methionine 14 mg / g of protein 112 mg total in 15 grams (1/4 cup)
(plus some others that I don't think ever play Ehrlich's game)
My BCAA supplement has in one heaping teaspoon (5.75 grams):
Valine: 500 mg / g of AAs (2,500 mg per serving)
Isoleucine: 250 mg / g of AAs (1,250 mg per serving)
Leucine: 250 mg / g of AAs (1,250 mg per serving)
So on a bulk basis it's as much as 18x more potent, and the ratios are different. 1 gram of BCAA supplement has 25% more valine than a 1/4 cup of dry yeast!
Questions remaining.
1. Are the Amino Acids in yeast "free" like they are in the powder?
Hypothesis, I doubt it. There's a century of experiments of dosing ferments with pure BCAA's and getting fusels, but I've never seen any analysis on the AA profile of typical feedstock causing high fusel yields. And from sour mashing to dunder it's not like supplementing ferments with yeast is a new thing so I suspect some of us would know if the AA profile of feedstock mattered much. Also, boiling a yeast bomb may empty the cells, it will denature proteins, but that just scrambles then it doesn't chop them up neatly into individual AA. I suspect at most AA in a yeast bomb are in the form of scrambled protein soup.
2. Are BCAA's even going to supply yeast with nitrogen they need?
Hypothesis, maybe not as much as other sources. For one, if the ehrlich pathway eats the BCAA's and makes fusels then they aren't there for the yeast anymore. For another, ammonia salts are super simple and just floating by freely, would a yeast really break down a protein to get to an AA to break it down and rearrange it if it already has the components?
3. Are yeast bombs even meant to supply amino acids? I would say no, that a yeast bomb supplies minerals, micro-nutrients, lipids and the like. It's less about feeding them what they need to metabolize and more about feeding them what they literally make themselves from. Sure, a yeast bomb contains some BCAA's, but only about a gram diluted into the whole wash. But they do have 100% of all the other "stuff" that it took to make a big pile of yeast bodies.
So, still some questions, but I'm less concerned about BCAA's in yeast bombs than I was before, thanks. Without balancing the equations it looks like at worst a yeast bomb might add as much as a ml of fusel oil to a wash from the ehrlich pathway. (I'm a nerd, so I'm sure I will do that at some point, but for now I need more coffee)
But Fermented Beverage Production has this more concise summary, and a teasing phenylethanol blurb:Higher alcohols are also produced by yeast, and these are important flavor
congeners. The main pathway for their synthesis is the Ehrlich pathway... An alternative
pathway involves pyruvic acid as a precursor... This latter
pathway occurs in amino acid deficient conditions, and is the main pathway for
the production of 1-propanol.
The branched alcohols active amyl alcohol, isobutanol, and isoamyl alcohol are
produced through the Ehrlich pathway from the branched amino acids isoleucine,
valine, and leucine, respectively. Branched alcohols are also formed as byproducts
of branched amino acid synthesis during the exponential growth stage of fermenta-
tion.
The amount and distribution of higher alcohols depends on temperature and pH.
Table 5.1 shows the effect of varying temperature in an open top fermenter from
20 ◦ C to 35 ◦ C. The higher alcohol content of all species is greatest at 30 ◦ C. At
20 ◦ C, the total abundance is the least, but some species are more abundant at 20 ◦ C
than at 35 ◦ C. The maximum higher alcohol abundance occurs when the pH is close
to 6.0, and the abundance is least when the pH is 4.0.
Malt distillery fermentations use very high pitch rates compared to brewery
fermentations: 2 × 10 7 vs 6 × 10 6 cells/mL, respectively. Experimental data
shows that increasing the inoculation level increases total higher alcohol production, leaving the proportions of alcohol species essentially unchanged. However, increased inoculation rate beyond distillery normal does reduce medium chain fatty acids (decanoic, octanoic, and dodecanoic) and their associated ethyl esters.
The typical distillery pitch rate of 2 × 10 7 empirically maximizes the production of
these compounds. Ramsay and Berry [678] speculate that the reason for this fatty
acid trend is the abundance of unsaturated fatty acids (lipids) supplied to the wash
by the inoculum. Commercial malt distillery inocula are typically aerobically grown, and so have an abundance of unsaturated fatty acids and sterols. Fatty acid production is diminished by the concentration of unsaturated fatty acids. This might not apply to bourbon and rye fermentations, on the grain, since the mash in
this case already has an abundance of lipids. According to Willkie and Prochaska,
Seagram, the inoculation rate for bourbon is 4 − 6 × 10 6 cells per mL of mash at a
minimum. Even accounting for the volume fraction of solids in a mash, this
inoculation level is closer to brewery levels than to malt wash levels.
Tables 5.3 and 5.4 show the results of experiments by Reazin, Scales, and
Andreasen of Seagram. The experiments compared five different mashes,
with the additions of radioactive threonine and isoleucine. The most striking
result in Table 5.3 is the observation that low free amino nitrogen (FAN) mashes
produce high levels of isoamyl alcohol. Guymon, Ingraham and Crowell
developed a hypothesis for this phenomenon known as the “keto acid overflow
theory”. It recognizes that yeast may form certain amino acids from corresponding α-keto acids and nitrogen. In nitrogen-deficient conditions, the keto acids accumulate (overflow). Their increased abundance leads to an increase in fusel alcohols by the Ehrlich pathway. The majority of the radioactivity due to isoleucine occurs as active amyl alcohol by the Ehrlich pathway (Figs. 5.2 and 5.3). In contrast, on the order of 10% of
threonine radioactivity forms propanol. Depending on mash, a substantial portion
appears as ethanol or active amyl alcohol. The appearance of radioactive ethanol is
attributed to the enzyme thronine aldolase which converts threonine into glycine
and acetaldehyde, and the aldehyde can be converted to ethanol with alcohol
dehydrogenase (XIII in Fig. 5.1). The appearance of threonine radioactivity as active
amyl alcohol occurs in nitrogen-deficient (low FAN) mashes and is due to the α-
ketobutyrate to α-keto-β-methyl-valerate reaction in Fig. 5.3.
The bold part is what caught my eye, but in the spirit of the OP, let's highlight a different part for a second "replacement of sugars such as maltose by glucose." Sounds like a technical way to say "sugar bite" is real.Higher Alcohols
Higher alcohols are produced from the carbon skeletons of amino acids. They may arise by the
decarboxylation and deamination of amino acids present in the wort or by a biosynthetic
route using the amino acid biosynthetic pathway of the yeast (Figure 2--4). Both these routes may
occur in the same fermentation, with a switch from the degradative route to the biosynthetic
route occurring when the amino acids in the wort have been metabolized. In general, condi-
tions that favor a high growth rate tend to stimulate the level of higher alcohol production.
These parameters include an elevated temperature, high inoculum levels, aeration of the
medium, and replacement of sugars such as maltose by glucose. These general effects will
increase the levels of all higher alcohols present in the medium; however, the levels of individual
higher alcohols can be manipulated by altering the amount of the corresponding amino acid in
the wort or must, or by genetically manipulating the organism so that producers may control the
amount of a given amino acid or higher alcohol.
This can be advantageous since certain amino acids induce a distinctive flavor; for example,
phenylalanine stimulates phenyl ethanol production, a higher alcohol that gives a roselike
aroma.
All that said, and I know I'm in a neutral thread, but the implications for flavor products in all this are more interesting to me. For neutral, of course start with the best wash you can, but like the plant you work at, if you want a neutral you're gonna have to make it in the still anyway, so worrying about a few ml's here and there may be unnecessary. You're gonna need a tall column, lots of reflux, strict cuts, more than one run through, and optimally a neutralization step as well, even if you start with the cleanest wash ever made.Utilization of Nitrogen Sources
S. cerevisiae can metabolize a number of nitrogen compounds. It can assimilate ammonia
readily through active transport and can grow well with ammonium as the sole source of nitro-
gen except for a few vitamins such as biotin and nicotinamide. Urea is also a good source of
nitrogen and is converted to ammonium within the cell (but you might not want it for other reasons - zapata). Nitrate and nitrite cannot be used. All a-amino acids can be taken up readily, as can small peptides. Proline can only be used under aerobic conditions, as its metabolism involves an oxidase-catalyzed step. The organic com-
pounds vary greatly in their ability' to sustain growth as single compounds, but mixtures of
amino acids tend to support the best growth. Yeast has no extracellular protease activity and
so cannot utilize large peptides or proteins. In industrial practice, as media tend to contain a
wide range of amino acids and ammonium, and in some cases urea may also be added, availabil-
ity of nitrogen is not usually a problem. In fact, the amount of assimilable nitrogen may be
deliberately restricted to give just enough yeast growth. This tends to improve the efficiency of
conversion of sugars to ethanol and CO 2 and makes the resultant alcoholic liquor less sup-
portive of bacterial growth.
Stibnut, thanks for your good write up. Yepp, I’m with you on esters and other things. Low alco contents of the “beer” turn many things upside down. And that "Begleitstoffesimulator" just illustrates it well. For instance, during the stripping run the most of fusels leave the pot before its temp gets 93 centigrade. Here’s my tip to get clean but unfortunately "late-headless" distillate in 3 runs.
Acidity reduction?
