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Malt Specifications values


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Can anyone here explain to me the PSY (potential spirit yield) from a malt specificiation?

It simply doesn't make sense to me. I looked at a bunch of different malt specs (malt analyses). Most of them, for malted barley for example, seem to be in the 400L/tonne range, that's 400L of pure alcohol per metric tonne of grain. Specifically looking at one which was 405L/tonne, that is 405mL/kg. That is an insane number, no way can you get 405mL of pure alcohol from 1kg of grain, you can even do that with 1kg of sucrose, it takes 1.19kg of sucrose to make 405mL of pure alcohol (1mol sucrose = 2mol EtOH, 2mol CO2), and that is under realistically unlikely ideal conditions.

So I don't really understand that value, there has to be something I'm missing. I'll most likely ignore the number in the future, but I'm curious what it's all about? 

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You are off by a factor of two.   Sucrose is a disaccharide, so 1mol of sucrose produces 4 mol of EtOH and 4 mol CO2.  You won't see much sucrose from malt, instead you'll end up with mostly maltose (another di-sacch) or glucose (a mono-sacch) if you use enzymes.

Yes, an efficient operation really can get >400LA from a metric tonne of grains tho' I more often see such high figures associated with corn rather than malt.

405 LA * (789 g/LA) / (46.07 g/mol EtOH) = 6936 mol EtOH

6936 mol EtOH requires the fermentation of 3468 mol of monosaccharide (2 EtOH/monosacch) or 1734 mol of disaccharide (4 EtOH/disacch)

3468 mol glucose * (180.156 g/mol glucose) =  624787g = 0.625 metric tonnes of glucose

1734 mol of disacc * 342.3 g/mol disacch) =  593554g = 0.594 metric tonnes of disaccharide.

[[ note the mass difference in sugar mass is just the mass of water needed to hydrolyse the dissach, iow 0.594 mton of maltose + 1734 mol water => 0.625 mton monosacch hexose sugars]]

The yeast consume ~3% of available carbon primarily for their mannose cell walls, so you'd need to extract (0.625 / 0.97)  = 64.4% of the malt mass as glucose to obtain the 405LA/m.tonne.

Too mathy ? A rule of thumb, for most grains and high extraction methods, 3kg of grist =>  1kg of EtOH,  1kg of CO2 and 1kg of waste

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>> no way can you get 405mL of pure alcohol from 1kg of grain

Yes you can, and the fuel-ethanol types do better than that regularly.   You may need enzymes to get to that with malt.

The other thing I'd say is that malt is expensive stuff, and used for it's unique flavor.   So flavor is generally more important than extractable starch.  If you aren't using exogenous enzymes for conversion, then of course the malt enzymes are critically important.


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3 hours ago, Foreshot said:

For the big guys they aim for ~440ml per kg. Brian Zeno from the Still Talking podcast talks about it on one of the episodes (not sure which one).

That's a very high figure and likely only applies to maize/corn with it's higher starch content.  USDA reports a fuel ethanol yield of 425.6 LA/mton (w/o cellulosic conversion) in 2014, and you are quite unlikely to match that in a 300gal step mash tun. 

"The Alcohol Textbook", 4th Ed, Jennsen 2003 has a table that can be converted to ... (LA/mton).

425 LA/mton  - finely ground corn (3/16" screen)

395 LA/mton - coarse corn (5/16" screen)

373 LA/mton - barley

358 LA/mton - rye

"Whisky: Technology, Production,Marketing" , Inge 2003, describes (then recent) Scotch extraction improvements using 'Chariot' barley malt

420 LA/mton - malt

'Science and Technology of Whiskies' by Piggott et al, 1989 cited a malt figure around 381LA/mton


Grist isn't the biggest expense per barrel and you shouldn't get too upset about 10%-ish lower extraction figures.



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  • 2 weeks later...
On 1/6/2020 at 9:12 PM, captnKB said:

You can reasonably expect 3 proof gallons per bushel from malted barley. This will be highly dependent on your cuts and quality of fermentation

3pg/bu is  223 LA/metric tonne, and should be read  readily achievable w/ malt, conventional beer-brewery &  non-enzymatic conversions.


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