Partial Mash Gravity Question

[nordoe]

So I just did my first partial mash. I used the instructions from Deathbrewer. Thanks by the way. Anyway, I think it went pretty well but my OG was pretty off. I was supposed to have an OG at 1.063 and I got 1.055 after adjusting for temperature. Is that a big difference or am I still in the ball park?

 

[BigB]

Thats pretty far off, but will still be beer. What was your recipe? What was your gravity after mashing/before boil?

 

[Poindexter]

I agree with BigB, it will still be beer.

One thing you can do is go back and calculate your house efficiency. Ocne you knwo what it was for the last batch you will almost instantly start having ideas abotu how to use your system more efficiently on the next batch.

Ocne you are consistently hitting 83-90% you are probably golden.

 

[nordoe]

The recipe was for a Belgian Wit. I used 4 pounds of grains in the mash. 2 lbs of 2 row, 1 lb of flaked oats and 1 lb of flaked wheat. After mash I used about 5.5 pounds of liquid malt wheat extract. Not sure for what my preboil gravity is because I only had about 2.5 gallons at that point. It was way high, is there a calculation to figure that out?

 

[BigB]

Well, I am going to guess one of two things happened:
1. After boiling and topping off with water, you didn't mix thoroughly and drew the hydro sample off the top. Since the wort is heavier, a thinner mixture would be at the top. If this is what happened, no big deal because the yeast will mix everything thoroughly during fermentation.

2. Your efficiency on your mash was low. This could happen for any number of reasons. Mash temp too high or too low, too little water, too short of mash time, poor mixing of the grains. If you used Deathbrewer's method, I would assume that you used 2 gallons of water for mash then 2 gallons for sparge. But to lose 1.5 gallons of water for only 4 lbs of grain seems extreme. I've never lost more than 1/2 gallon for 4-5 lbs.

To calculate efficiency you can use the method that Palmer explains here in How To Brew.

 

[TheGeek]

I had a similar mishap with my first partial last week. I was a good 8 points off my calculated (with BrewPal) gravity. I think my mistake was with the software however, where I did a 30 minute steep, it may have assumed a 60 minute lauter. In any case the next time I do a partial, I'm going to do the calculating myself instead of letting the software do it, and see what the difference is.

 

[nordoe]

Well, I am going to guess one of two things happened:
1. After boiling and topping off with water, you didn't mix thoroughly and drew the hydro sample off the top. Since the wort is heavier, a thinner mixture would be at the top. If this is what happened, no big deal because the yeast will mix everything thoroughly during fermentation.

2. Your efficiency on your mash was low. This could happen for any number of reasons. Mash temp too high or too low, too little water, too short of mash time, poor mixing of the grains. If you used Deathbrewer's method, I would assume that you used 2 gallons of water for mash then 2 gallons for sparge. But to lose 1.5 gallons of water for only 4 lbs of grain seems extreme. I've never lost more than 1/2 gallon for 4-5 lbs.

To calculate efficiency you can use the method that Palmer explains here in How To Brew.

thanks for your reply. I bet it was the efficency of the mash. It was difficult to keep it at the temp. It would drop down, so I would add some flame. Also I used 1.5 gallons of water for the mash and another 1.5 for the sparge.

 

[breez7]

I kind of have a side question for partial mashing. How do you calculate what your OG will be when you take a gravity reading before the boil but expect to lose a gallon or so. For example: right before the boil I take a gravity reading of 1.050 out of six gallons, what would that gravity be post boil around five gallons??? Does this make sense? I'm terrible at math!

This way I will know if I need more or less DME before I begin the boil.

 

[dcp27]

Pre-boil OG * Pre-boil volume / post-boil volume = post-boil OG

so in that case 50 * 6/5 = 60

 

[dcp27]

thanks for your reply. I bet it was the efficency of the mash. It was difficult to keep it at the temp. It would drop down, so I would add some flame. Also I used 1.5 gallons of water for the mash and another 1.5 for the sparge.

I think part of the problem was the calculated OG was based on about 85% efficiency, which probably won't happen on your first go around. you hit around 65%, which isn't bad, just not great. Better temperature control and a multi-sparge will certainly help that.

 

[nordoe]

I kind of have a side question for partial mashing. How do you calculate what your OG will be when you take a gravity reading before the boil but expect to lose a gallon or so. For example: right before the boil I take a gravity reading of 1.050 out of six gallons, what would that gravity be post boil around five gallons??? Does this make sense? I'm terrible at math!

This way I will know if I need more or less DME before I begin the boil.

It does make sense to me, but I still don't know the answer. I was doing a partial mash and a partial boil. I started with 1.5 gallons mash and sparged 1.5. I probably lost a half gallon. I did take a pre boil reading but it was way high. I am sure it was do to the fact I was measuring 2.5 as opposed to 5 or 6 gallons. I don't know if there is a calculation to adjust for pre boil volume size on a partial boil. Can someone else chime in?

 

[ChshreCat]

An easier way to keep your mash temp is to use your oven. Set your oven on it's lowest setting and when it's warmed up you just pop your mash pot in there and turn off the heat. The residual heat of the oven will keep your mash warm much longer than sitting on the stove. When you open it up to stir, just turn the oven back on for a minute to warm it back up and you're good.

I use an oven thermometer to try to hit my oven temp just a couple degrees above my mash temp before turning it off, but you don't even have to be that exact.

 

[breez7]

Pre-boil OG * Pre-boil volume / post-boil volume = post-boil OG

so in that case 50 * 6/5 = 60

Thanks that will help me a lot!

 

[BigB]

And easier way to keep your mash temp is to use your oven. Set your oven on it's lowest setting and when it's warmed up you just pop your mash pot in there and turn off the heat. The residual heat of the oven will keep your mash warm much longer than sitting on the stove. When you open it up to stir, just turn the oven back on for a minute to warm it back up and you're good.

I use an oven thermometer to try to hit my oven temp just a couple degrees above my mash temp before turning it off, but you don't even have to be that exact.

Damn Cat, thats not a bad idea. I think that would be a pretty good way to control temps. But, overall, I have had no issues maintaining temp. I typically strike at about 10-12 degrees above mash temp and simply wrap my brew pot with a towel. I can usually maintain within 2 degrees for an hour. Now, when I'm brewing, the wife stays out of the kitchen and I don't have any kids, so I don't have to worry about someone messing with the stove.

 

[ChshreCat]

Damn Cat, thats not a bad idea.

Yeah, I'm brilliant, I know.
I stole the idea from Ed Wort.
It's hard being as smart as I am.

 

[nordoe]

how about covering the brew pot and then sticking it in a cooler? Has anyone tried that.