This is a little something i have been doing on the side. Let me know what you think, and if it is pertinent.
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Conversions that this guide will be working off of, if you want to use a different conversion, be my guest but make sure it is correct. Also remember that weight and volume are not interchangeable in most cases, only with water is this acceptable. It is better to think of water as an exception rather than the norm in most cases.
1kg = 2.205lbs 1 gallon = 3.785 Liters
1kg = 1000g 1L = 1000 milliliters
1 fluid ounce = 29.57 mL 1 ounce = 28.35 grams
1 gallon of water = 8.34lbs 1 pound = 16 oz.
This is pertinent to the next few calculations we will be going through based on the weight of starch to the weight of water. You can only compare two like things with the same units; different units of measurement must be converted, kind of like fractions back in middle school. Each fraction must have the same denominator before they can be added or subtracted, more or less the same thing here.
Typical suggested ratios of water: grain, range from 2.5:1 to 4:1. Now it is possible to go lower than 2.5lbs water to 1lb grain, just be sure to dial in your equipment before trying for the thicker mashes, otherwise inefficiency can result.
Also remember that starch is different than grain, very obvious observation I know, but it needs to be said. Most whole grains such as corn, barley, rye, wheat, etc. will be comprised mostly of starch, but they have other goodies in there as well. Usually your grain provider will give a sheet that designates how much starch, beta-glucan, protein, etc. is in the batch of grain you purchased. Use that starch content % for your calculations. If purchasing actual starch, which has been processed by someone else, it should be 90-100% pure starch, and no corrections need to be made to compensate.
This is applicable for the amount of enzymes needed to convert the starch to sugar, not for the calculation based on mash tun size. This can also be used to calculate theoretical sugar yields for each individual mash.
Hypothetical Situation 1:
Mash size
We have 600 gallons of water, and we want to run a 4:1 ratio (water: grain) in this mash. We will be mashing 100% unmalted barley where the barley starch content is 65%.
600 gallons of water x 8.34lbs = 5004lbs x 1/4 (4:1 ratio) = 1251lbs of barley.
This means we should add 1250lbs of barley to 600 gallons of water to achieve our desired ratio. This will increase the total volume of the mash, so make sure you have a 800-1000 gallon capacity mash tun.
Theoretical yield
1250lbs of barley at 65% starch content.
1250 x .65 = 813lbs of pure starch = 813lbs of sugar (assuming no losses and full conversion)
813lbs sugar/5004 lbs. water = 16% sugar solution (roughly) or 16.24g/100mL (exactly)
It is good to know the theoretical yield as this will then show whether there are some large inefficiencies in the mash, and will let you know to start looking from problem spots.
Hypothetical Situation 2:
Mash Size
500 gallon mash being run at a 2.5:1 ratio, with wheat starch (premade) at 95% starch content.
500gallons water x 8.34lbs = 4170lbs of water x 1 / 2.5 (2.5:1 ratio) = 1668lbs of starch
Running at this ratio, we can add 1668lbs of starch to the 500gallons of water to achieve our desired results. Once again make sure you have a mash tun large enough to accommodate the total volume increase when the starch is added to the water.
Theoretical Yield
1668 lbs. of wheat starch at 95% starch content.
1668 x .95 = 1585lbs of starch = 1585lbs of sugar (assuming no losses etc.)
1585lbs sugar/4170lbs water = 38% sugar solution (roughly) or 38.34g/100mL (exactly)
Be careful of running a mash this high on sugar content, the high osmotic pressure can reduce yeast productivity, or even kill them before their job is done.
Percent yield
Let's say we got a 34% sugar yield out of this mash as our actual yield. We can then compare that versus what the theoretical yield is to get the % yield. This will allow us to calculate the discrepancies if necessary.
Actual/theoretical x 100 = % yield.
34/38 x 100 = 89.5% yield
Not especially necessary with the calculations that we already ran, but it can be useful if working backwards, or trying to do a compare/contrast experiment. Because 4% sugar loss can happen in two separate mashes, but if one is supposed to have 24% sugar, and the other 38% sugar, the 4% loss is different between the two.
20/24 x 100 = 83.33% versus 34/38 x 100 = 89.5%
This is not an easy concept to grasp, but once it is harnessed, this concept can provide a vast improvement in quality and consistency in a distillery. "Distilling is 75% science, and 25% art" a wise man once said, don't forget the science part.