Pre boil gravity

[OAE Iceman]

I brewed a nice large beer two weeks ago with 17.5 pounds of grain. The calculations said my beer should have a FG of about 1.080. I did take a pre boil sample of the wort, set it aside and let it cool down to 68 degrees. I had a 90 minute boil on this beer and when I had 20 minutes left in the boil, I remembered the sample I took and went to check it. It was at 1.055 at 68 degrees. Pretty low. This is the first time I have ever did a pre boil sample with the hydrometer. I decided to toss in some DME and put in a 1/2 a lb. At the end of the boil I rechecked the gravity and it was 1.079 at 68 degrees. Did I get lucky on this? How much different would the end boil gravity have been if I did not add the DME? I used a large yeast starter of British 1068 and I checked the gravity yesterday and it hit 1.012! I am now dry hopping it. O yea, I did a batch sparge and instead of a fly sparge.
Thanks! Can't wait to drink this stuff!

 

[Threefold Brewing]

I was having troubles hitting my pre boil gravity not too long ago. I check with my refractometer, and a hydrometer sample. Even after a 90 minute boil I was still under target. I eventually isolated my problem to sparge efficiency.

One technique I've been using with great results is after I pull the first running, is to run it through the grain bed a couple more times, and then repeat with the sparge (if batch sparging) This is to ensure you really collect ALL of the remaining sugars without adding more sparge water and lowering your pre boil gravity.

Try it out and let me know!

 

[LarryBrewer]

+1 on recording your pre-boil gravity for the first time!

I recommend using the brew feature, specifically to record log entries for mash complete, pre-boil, boil complete, and brewday complete. That will give you complete efficiency numbers. Very handy for tracking down where the problem might be. Crush, mash pH, mash temp/time, all factor into it. By recording these brew logs, the system will help point out it was a problem with conversion (in the mash tun), or a lautering issue (transferring from the mash tun to the kettle).
http://www.brewersfriend.com/faq/#brewsessions5

The recirculation idea is pretty neat!

I've noticed I get additional conversion even after a 60 minute mash at 152F. I am keeping a spreadsheet with detailed notes. After I get a few more brews done I'll publish the results. A hypothesis is conversion is still happening after 60 minutes. Your efficiency boost might not be due to the recirculation at all, instead due to the extra exposure. The way to test that would be to take a gravity reading before and after doing the recirculation.

 

[LarryBrewer]

I decided to toss in some DME and put in a 1/2 a lb. At the end of the boil I rechecked the gravity and it was 1.079 at 68 degrees. Did I get lucky on this? How much different would the end boil gravity have been if I did not add the DME?

8 oz in a 5.5 gallon batch would give + 0.004 gravity points.

 

[OAE Iceman]

Thanks for the information!

 

[LarryBrewer]

FYI - I came up with that figure by making a 5.5 gallon batch in the recipe editor, and adding only 8oz of DME. The recipe editor can be used for doing recipe simulations too. Too bad we can't taste the simulated beer yet.

 

[Nosybear]

It's an easy calculation to do by hand: DME should contribute 45 points per pound per gallon, efficiency is 100% (there is no conversion loss). Using 1/2 pound gives 22.5 points, dividing by 5.5 gives 4.01 points (You can ignore the decimals) for a half-pound of DME in 5.5 gallons of wort.

 

[Kevin The Stout]

It's easy to work out how many points you're adding with DME, but it's not always easy to determine how many points you have in your wort from a pre-boil gravity reading. With my last brew, http://www.brewersfriend.com/homebrew/recipe/view/56670/skull-splitter-clone, I got a suspiciously high 105% pre-boil efficiency. So confident was I that I'd been pessimistic with my predicted brew house efficiency I added a litre of water to the boil. Post chill I took another reading and I was 4 points under target. A total of 200 points had gone AWOL during the boil. I know this is a commonly reported problem and people usually blame bad temperature compensation or poor gravity readings, but I know exactly where those 200 points went. They were the break material at the bottom of the kettle.

The pre-boil measurement is measuring the combination of all the sugar and protein dissolved/suspended in the wort. What is difficult to determine is the amount of protein that will precipitate out as break. Probably the best you can do is, as Larry says, record everything and try and correct for it next time. My case is probably particularly bad due to very proteinacious malt, a simple lauter tun and possibly my milling.

Falling 4 points short wasn't a problem though. I always put only clear wort in the fermentor. Everything else goes into demijohns where it's left for day, the clear wort racked off, boiled, cooled and added in to the now active ferment. This time I collected 3.65 litres of clear wort from the demijohns. I boiled this down to 2.5 litres before adding it to the wort. That bought the total gravity up to 1.085 and since it's a Scottish Ale I figured a little caramelisation couldn't do any harm.