My Plan to Hit OG Every Time

[Oberon]

I've recently overhauled my equipment and have been thinking a lot about my process. I use a 15.5 gallon Bayou Classic pot with turkey fryer basket and a custom voile bag that fits the basket. I've only brewed on it once but really like this setup.

After the mash I hoist the basket above the water, turn the heat on, and stir to drain the water from the mash. I can get the grain much drier than I was ever able to squeezing. I didn't rinse the grain (suedo-sparge) last time but it would be really easy.

My plan is to take a gravity reading using my refractometer after the grains are dry. If I know volume, gravity, and boil rate I can figure out what original gravity will be based on what the pre-boil gravity is. If its a little low I can sparge, stir, and take another reading.

Let's say I want an OG of 1.050 with a 5 gallon batch (50*5=250 gravity "points") and assume my boil rate is 2 gph (round numbers for simplicity). If I have 6 gallons after the mash my gravity reading should be 1.042 (250/6). If I come up a little short I can spare with 1/2 gallon and take another reading which should be 1.038 (250/6.5=38). Once I get the pre-boil gravity I need I can just dump the rest of the sparge water in the kettle and wait for the boil. I could even go above the water I need and just add hops when I get to the level I need.

Does this make sense? Is my thinking sound? Does anyone else do this?

 

[bredle]

I am getting ready to do my first BIAB (Bell's Two Hearted Clone) and this reasoning sounds pretty good to me!

 

[KIAKillerXJ]

sounds good except your sparge may not give you sugars in the same proportional way that you are thinking. It may take more than a your proposed half gallon to make up for those gravity points.

 

[jCOSbrew]

I would assume that you won't significantly improve efficiency with the sparge/rinse step. You can adjust your OG by adding less water (or boiling off more water) or by adding some DME based on your pre-boil volume and gravity.

After a few batches you should have a good idea of the brewhouse efficiency of your process and can adjust the recipe to match your efficiency number.

 

[Oberon]

sounds good except your sparge may not give you sugars in the same proportional way that you are thinking. It may take more than a your proposed half gallon to make up for those gravity points.

You might be right. Maybe I'll have to do one gallon at a time or just dump all the sparge water over the grains at once.

I'll report back if I ever get to brew again. I dropped my pot off for a new weld nearly three weeks ago and still don't have it.

 

[Oberon]

I would assume that you won't significantly improve efficiency with the sparge/rinse step. You can adjust your OG by adding less water (or boiling off more water) or by adding some DME based on your pre-boil volume and gravity.

After a few batches you should have a good idea of the brewhouse efficiency of your process and can adjust the recipe to match your efficiency number.

What is the difference between DME and extract left behind in my grain? The grain is still pretty sticky when I pitch it so I assume there is sugar left behind.

My plan is my fine tune attempt so I don't have to settle for "close". I think my math works. I was hoping someone has already used this method.

 

[Carlscan26]

Once I get the pre-boil gravity I need I can just dump the rest of the sparge water in the kettle and wait for the boil.

If you do that then you will dilute the liquor and change your gravity. It's a balancing game; adding water to get to your volume will affect your gravity.



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[KIAKillerXJ]

^ Yup. So yes, you will likely rinse at least some more sugars, though probably not at a proportional rate, and since you will end up with more wort, you will have to increase boil times to concentrate everything down.

 

[Oberon]

If you do that then you will dilute the liquor and change your gravity. It's a balancing game; adding water to get to your volume will affect your gravity.



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My thinking is that I just need a certain amount of total sugar. I can figure out what the total sugar is by using the "gravity point" method outlined in the OP. I don't really care about the pre-boil gravity but I do care about the original gravity and getting the volume I want into the fermenter (usually 5.25 gallons). I would add the water I need for the recipe. I think if I hit my desired pre-boil gravity at a particular volume my OG will work out. If I hit my desired pre-boil gravity before I spare I should be able to skip sparging and just dump the extra water into the kettle.

Basically, from what I have read sugar doesn't boil off and the concentration of sugar is linear. For instance 1 gallon of 1.050 wort (1*50=50) has the same amount of sugar as 5 gallons of 1.010 wort (5*10=50). If that is true I think my idea* should work.

*Its probably not my "idea" as much as my "understanding".

 

[Carlscan26]

My thinking is that I just need a certain amount of total sugar. I can figure out what the total sugar is by using the "gravity point" method outlined in the OP. I don't really care about the pre-boil gravity but I do care about the original gravity and getting the volume I want into the fermenter (usually 5.25 gallons). I would add the water I need for the recipe. I think if I hit my desired pre-boil gravity at a particular volume my OG will work out. If I hit my desired pre-boil gravity before I spare I should be able to skip sparging and just dump the extra water into the kettle.



Basically, from what I have read sugar doesn't boil off and the concentration of sugar is linear. For instance 1 gallon of 1.050 wort (1*50=50) has the same amount of sugar as 5 gallons of 1.010 wort (5*10=50). If that is true I think my idea* should work.



*Its probably not my "idea" as much as my "understanding".

You have it but yet you don't...you want an OG with a certain post boil volume. Based on your boil time and boil off rate you can calculate your preboil volume and SG. That's the equations you originally posted. And those pre/SG and post/OG are ratios to each other. You are correct the sugar does not boil off so as the volume decreases the gravity will increase.

So if you have your SG but are low on volume then adding more water throws off that ratio. You have to remeasure the SG with the final preboil volume. What you seem to be saying is that you can get the SG and then adjust the volume but still expect the same OG with the same final volume...which won't work. If one side changes the other side has to also.



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[Doongie]

In your initial description using 250 gravity points in 6 gals, you mention sparging 1/2 gal and still having 250 points. That sounds like adding water, sparging should add points as it is bringing more sugar off the grain. If you think it will give you the same .021 points the other half gallons averaged, you will be disappointed.
Your basic understanding is correct, but your math is a touch off.

If your preboil gravity is off, you have a couple choices. If it's low you can calculate and boil off more and keep a smaller final volume of the anticipated OG, or add extract (lme, dme, or from sparging your grain) to hit your pre boil number so you can have the final volume AND OG you wanted. If it's high you can accept a higher gravity beer or add water and have a higher volume of the anticipated OG than what you expected.

If you are low and want to boil off the normal amount but you want to know what that lower final volume will be so you can decide between that or adding extract, then calculate the total points you actually have (measured pre boil sg (temp corrected)-1.000 x volume in gallons), then divide by the OG you want post boil and the result will be your actual final volume in gallons. This will be at the correct gravity because you used that value in your calculation.

Keep in mind, boiloff rates can be affected by ambient conditions, so it is not a perfectly consistent process, but pretty darn close usually. You may see a difference between a brew day in Aug vs Feb, but not much change from Jun to Jul.

One way is to plan the brew so your post boil volume is less than the final quantity you want, but with a higher gravity, take a measurement, then calculate and add water till the gravity is what you want, then keep the actual final volume you want and discard any extra. I.E. Plan so post boil is 4.5 gallons and a few points high so adding 1/4-3/4 gallon will put your OG spot on. If you calculate close, you can get to a point where you don't waste any, but also account for small fluctuations in your mash efficiency, yet still hit your OG bang on EVERY time, with only slight variations in final volume.

 

[Oberon]

Thanks for the feedback. I ended up hitting the preboil gravity I wanted but neglected to take into account the dead space in my pot which caused a slightly low OG. I brewed a very low IBU lambic and planned a slightly larger batch than usual so I was able boil a bit longer and steal some wort from the dead space. I was shooting for 1.050 and hit 1.045 so good enough.

After doing a few batches on my current system I can see with more clarity what adjustments I can and cannot make. I know my volume at any given time and with a refractometer also know my specific gravity. It has been really cold in Michigan this year so I'm not exactly sure what my boil rate is but I'm getting things dialed in better than my previous system. The two batches I've brewed on the new system were within 2% mash efficiency so that is good.