Thursday, August 16, 2007

TBN + First Wort Gravity

Way over at The Brewing Network, a fellow forum user had asked if there was a spreadsheet that performs John Palmer's water addition for step-mashing calculations. It seemed a good enough reason to put one together, so that's what I did. If you download the spreadsheet that I make available, you'll notice that you can do the calculations in the tab labelled "Infusion Calculations." Let me know what you think if you end up using it.

Also, I stumbled upon this when searching for a way to solve a friends problem with doing AG in a 20 quart kettle on a stovetop. He was fretting about having a 20 quart brewpot and trying to do a full 5 gallon all-grain batch on his stovetop. We talked a bit about sparging, and it occurred to me that he could do a no-sparge brew if he had volume concerns. Of course, it struck me that I didn't know exactly what sort of original gravity to anticipate from first runnings, so I consulted Google. Lo and behold, I was granted the following from an old post on

As Ashton notes, Kunze* suggests that a first runnings of 20 Plato can be achieved by mashing 100 kg of malt with 3 hectoliters of water. Being from the US, these numbers don't mean a whole lot to me. Let's see what we get when we convert.
100 kg = ~220 pounds.
3 hectoliters = ~ 79.2 gallons, or ~317 quarts.

We then divide 317/220 to get ~1.44 quarts per pound. So, we now know the ratio in US units.

Ashton then goes on to provide a calculation for determining degress Plato of your first runnings from the mash thickness, assuming that Kunze is correct. It looks like this:

First wort gravity = (3 hl/100 kg malt)(20 Plato)/(3.2 hl/100 kg malt)
First wort gravity = 18.75 Plato

Of course, one can't just replace the "(3hl/100 kg malt)" with "(317g/200 lb malt)" and expect to get the same type of answer.

However, we can quickly determine a factor to make this easy. 3/100 = 0.03. 317/220 = 1.44. These two figures are separated by a factor of 48. That is 0.03*48 = 1.44 and 1.44/48 = 0.03.

Let's call (hl water/kg malt) Rm. In this case, Rm = 0.03. Let's call (quarts water/lbs malt) Ru. In this case, Ru = 1.44. 1.44/48 = 0.03. Likewise, if you wanted to determine the Rm for, say, 1.25 quarts per pound. Simply divide 1.25/48. The result is approximately 0.026. That is, it's the same ratio as 2.6 hl to 100 kg malt. Things are looking a bit simpler now.

To determine the degrees Plato of the first runnings of a mash with a water:grain ratio of 1.25 quarts per pound, we do the following.

1.) Divide 1.25 by the factor of 48. 1.25/48 = 0.026. That is 2.6 hl/100 kg malt.
2.) First Wort Gravity = (3hl/100 kg malt)(20 Plato)/(2.6 hl/100 kg malt)
3.) (0.03*20)/(0.026)
4.) (0.6)/(0.026) = ~23.1 Plato, = ~1.092 SG.

Long story short - here's an ultra-simple calculation that you can do to figure this out without exploding your brain:


Replace X with your quarts per pound ratio (1.5, for example), and it will spit out the gravity of your first runnings in degrees Plato. Ta da!

In Excel speak, =SUM(0.6)/(B1/48)

Okay, so all the math is there, but does it work? After all Kunze notes his results are based not just on a ratio, but on a much larger amount of grain and water than the typical homebrewer can handle. If I mash ten pounds of malt at a rate of 1.44 quarts per pound, can I also expect to get a first wort of 20 Plato (~1.080 SG)? I don't know. This, to me, is the most interesting part. Experiment designs are currently being considered. I'll be sure to post about it as this side project gains more momentum.

Lastly, I want to create a better logo for the top of the page. I was thinking of putting the title of the blog into a sort of faux-calculation. For example, 'Makin'' might be translated to m4(k)/n. I haven't tried to "convert" 'them there beers' as of yet, but I'll post when I think of something. Suggestions, as always are welcome.
Happy Brewing!

*That is, Wolfgang Kunze. Author of the highly respected Technology Brewing and Malting.


Kai said...


I came across your bog while searching for other brewer’s experiences with thin mashes. You have a nice write-up on thin mashes here in these two parts. But my experience with thin (1.5+ qt/lb) mashes is that they provide greater extraction of wort and don’t effect the fermentability. This data is supported by Briggs’s “Brewing and Malting Science” and Kunze’s “Brewing and Malting Technology”. The problem with thick mashes is that while they keep the b-amylase alive for longer they make it harder for the starch to gelatinize and the a-amylase to break it down. The end result (at least for the experiments that I did) was that thin mashes showed better conversion of the starches.

here is an article that you may want to check out:


Kai said...


Calculating the first wort gravity is actually easier than this:

% Plato is defined as (extract weight)/(extract weight + water weight). So when you mash 100 kg of malt with 300l (=300kg) of water and assume a malt extraction potential of 80% you get 80/(80+300) = 21 Plato. This is basically the number that came from Kunze. But this assumes that all of the starch in the mash is converted something that is oftentimes not the case. Especially if the crush is too coarse or the pH is suboptimal. It depends on the mash conditions how much of this gravity potential is actually realized and you can use the ratio between first wort gravity and calculated best case FW gravity to evaluate the efficiency of the conversion process and this becomes part of your extraction efficiency after you incur more losses during lautering.

BTW, a mash thickness of 3l/kg is actually on the low end for German mashed. Around 4 l/kg is more common.


PS: can you move or remove the comment about mash thickness that I accidentally posted to the wrong article. Thanks.