Partial mash OG too low. Ideas why?

[digphish]

So this is my second parital mash attempt. The first was a hefe that went well. I over shot my gravity and came out at 1.062. So I tried "hophead's" Flat Ass Tired--fat tire clone. However, I needed to convert his recipe to partial mash. Here is what he called for:

6lb 2-row
2lb amber malt
1lb munich
.5lb biscuit
.25lb 10L
.25 40L
.25 special roast

I converted it to:
4.2lbs extra light dme (figured 6-lb 2 row + 1lb amber = 7lbs grain x .6= 4.2lb dme)
1lb Amber
1lb munich
.5lb biscuit
.25lb 10L
.25 40L
.25 special roast

So following death brewer's parital mash instructions, I used 1.25qt/lb which came to about 1 Gallon. I mashed at 152 for 60 minutes, then sparged in 2 gallons of 170 degree water for 10 minutes. drained and combined worts and brought to boil. Brewed as usual with hop additions at 60 min, 30 min, 15 min, 5 min. At 15 minutes I also added irish moss and the DME. Cooled wort to 72 and put in my glass carboy (which is the first time using glass). Added about 2.5 Gallons of cool water to bring the total volume to 5.25 G. I then shook it as well as I could and pulled a sample that showed 1.030. Thinking that this was way low, I shook the carboy again, and pulled and got 1.030. Did I do something wrong? Was it the recipe? Or do you think that most of the wort sunk to the bottom of the carboy, and the beer is probably around 1.050? If the latter is the case, why can't I get a good reading any more? I used to have no problems getting accurate readings, but it seems like lately I have been having issues with my gravity.

BTW, it is bubbling along nicely 8 hours later!

Thanks for any and all feedback.

 

[dcp27]

considering 4.2# of DME itself in 5 gallons is above 1.030, I'm guessing your wort just sunk. next time just remember to pull a sample before topping off.

 

[pkeeler]

What temp was your sample at?

 

[digphish]

about 70 degrees

 

[mojotele]

considering 4.2# of DME itself in 5 gallons is above 1.030, I'm guessing your wort just sunk. next time just remember to pull a sample before topping off.

This is true. Assuming your volume is correct and you measured your DME correctly, that amount of DME in 5.25 gallons should give you 1.035. So, any one of these happened:

• You measured the DME incorrectly
• You measured your final volume incorrectly
• The wort didn't mix well with your top off water

In addition to taking a gravity reading before topping off, I'd recommend taking a gravity reading of the wort just after your mash and before adding extract. If you don't get the efficiency you were expecting, you can add more DME to compensate.

 

[digphish]

Mojotele,

I did measure the DME correctly as I added 1 3lb bag, 1 1lb bag, and measure out .25lbs from the last 1lb bag, so that isn't it. The final volume should be correct as I just calibrated my carboy this week, adding 5 Gallons and marking the outside, and then adding another 5 gallons and marking accordingly. I topped off to 5.25G, so that isn't it. I really think it was that I didn't mix my top off well enough.

Couple of questions:

How exactly do I measure my efficiency?

If I measure my wort once cooled, won't it show abnormally high since it is concentrated?

Thanks

 

[mojotele]

Mojotele,

I did measure the DME correctly as I added 1 3lb bag, 1 1lb bag, and measure out .25lbs from the last 1lb bag, so that isn't it. The final volume should be correct as I just calibrated my carboy this week, adding 5 Gallons and marking the outside, and then adding another 5 gallons and marking accordingly. I topped off to 5.25G, so that isn't it. I really think it was that I didn't mix my top off well enough.

That's cool. I just wanted to cover every possibility

How exactly do I measure my efficiency?

Very loosely put, your brewhouse efficiency is a ratio of the gravity you got vs. what you can possibly get from the grain in question. Basically, you have to find the potential of your grain and figure out how much you would get fully converted and with perfect lautering. Then measure the gravity of your wort after the mash and sparge. The ratio of the two will give you your efficiency in a percent value.

There's a lot of information on how to do this around the forums, on the internet, etc. A really good resource is BrauKaiser's website, but that can be really intimidating. The easiest way to do it is probably to use brewing software.

If I measure my wort once cooled, won't it show abnormally high since it is concentrated?

Yes, but if you know the volume of the wort it is easy to adjust it for your top off water. For instance, assume your gravity before adding top off water is 1.050 (50 "gravity points"). You have 2.5 gallons of wort. You want 5.25 gallons. All you need to do is this:

(2.5/5.25)*50 = 23.80952

So your gravity will be about 1.024 after adding the top off water. The "Dilution Tool" in Beer Smith does the exact same thing.

 

[digphish]

Thanks for that equation. I may start doing that for now on as I have been having the issues with measuring gravity lately. I'm brewing again Saturday, so I might try both ways and see if they come out the same. If not, I'll go with the one that looks better!

 

[mojotele]

Sounds good! FYI, measuring the gravity pre-top off and doing that dilution equation should always be more accurate.

 

[digphish]

I just brewed my raspberry wheat and tried the equation. I had about 3.3 Gallons of wort cooled to 75 degrees. OG was 1.110. I topped it off to equal 5.25 Gallons. According to the equation, my OG was 1.069. My measured OG after top off was 1.040. I think I'm going with the equation for now on as I can't seem to be able to properly mix the wort and water. I also took a sample of the wort after mash (while the grain was sparging in the other pot) and the gravity measured at 1.075 so I know I got a good conversion. Thanks again for the equation!!

 

[mojotele]

Yeah, go with the dilution equation. It's REALLY hard to mix in the top off water completely.