Parti-gyle rule of thumb

I wonder if anyone has any experience as to what the OG of the FIRST half of an all-grain run-off would be. For example, if I make a 6 gallon batch using an 8 gallon boil, is there a rule of thumb for what percentage of sugars I'm going to get in the first 4 gallon run-off?

I have read somewhere that the first third of run-off has half the sugars. True?

Just for fun, I made a graph using this info and assuming a curve that passes thru the "one-third equals one-half" point is valid, it looks like the first half of the wort would have 63% of the sugars.

Have I confused everyone?

This is really going to depend on your process and system. This is where you could really justify a refractometer as you could measure your gravity quickly and easily while sparging and stop once you have your desired gravity points for the first beer.

Very interesting question. I use batch sparging and have been recording the gravity of the run offs just because I thought they might be usefull some day. Could you post your data and graph?

Here is some info that may be helpful.

http://www.brewingtechniques.com/library/backissues/issue2.2/mosher.html

desertbronze said:

Here is some info that may be helpful.

http://www.brewingtechniques.com/library/backissues/issue2.2/mosher.html

Click to expand...

I've looked real hard at Mosher's numbers and there seems to be an inconsistency that has been bugging me. He lists a 50/50 split batch as 58% suagrs in the first half, 42% second half, but the chart he links shows it as 2/3 first half, 1/3 second half. If you try to graph this, the same thing occurs. He states that 50% of the sugar is in the first third of the runnings. This is confirmed in his first table as well as later in the article when he mentions making 3 beers and they would be roughly 24 Plato, 16 Plato, and 8 Plato, which is 1/2, 1/3, and 1/6 of the sugar extracted, respectively. If you plot this on a graph, you get the the first one below. (Note: 100% of sugars extracted means 100% of the sugars you plan on collecting, not that you are getting 100% efficiency). If you add in the point of 50% runnings collected at 58% of sugars, it just doesn't fit the graph (second one). A better fit is 69% of sugars at 50% collected (third one). In theory, this should follow an exponential curve, something like 1 - e^x, where x is some small negative number. I could go into more detail if anyone cares.

jcarson83 said:

Very interesting question. I use batch sparging and have been recording the gravity of the run offs just because I thought they might be usefull some day. Could you post your data and graph?

Click to expand...

Good point - I also batch sparge. Seems to me that you could dial in your batch sparge process to hit your desired gravities by varying the amounts of mash and sparge water. I need to check my notes.

I'm going to try this with an upcoming batch...I was just going to collect the runoff in 3 or 4 different batches, take the gravity of each, and then blend them as needed to get the target pre-boil gravities and volumes for each of the 2 beers.

Seems easier than trying to calc a target and constantly monitor the runoff gravity.

I did something similar on my last batch. I ran off the first 5 gallons via fly sparge into my primary kettle and then simply swapped vessels to a secondary kettle and kept sparging for another 2.5 gallons. I checked the gravity of the first and then the second and did the calcs and combined what I needed to hit my target gravity (1.060). Worked like a charm.

It seems to me that 3/4 of the gravity was extracted in the first 2/3s of the sparge.