Pre-boil gravity readings?

[RedGlass]

Is there any point to taking pre-boil gravity readings if I'm using BeerTools to calculate my efficiency? I have always taken one, but the software calculates efficiency based on OG. Should I even bother with it anymore?

 

[wcarter1227]

The only reason to really take the preboil readings is sometimes if you dont have the best efficiency and you dont get a full conversion you can either add dme to boost it up or its also good to know if your like me and sometimes over sparge and miss og so i have to boil extra time to boil off some water

 

[Catt22]

It's useful to know the pre-boil gravity as you can use this to predict the OG at the end of the boil. IOW, this gives you the opportunity to do something about it if it's much off your target. The gravity can be increased either by adding some DME or extending the boil to concentrate the wort. You can add some water during the boil to dilute the wort if the gravity is too high. There are a few things you need to know in order take advantage of the pre-boil reading. You need to have a fairly accurate estimate of the volume in the kettle and your boil off rate per hour. The calculation is simple and uses gravity units. The gravity units are simply a product of the decimal portion of the specific gravity (ie for 1.040 just use the 40) or points as they are often referred to. So, lets say you have 7.5 gallons of 1.040 wort and want to boil it down to 6 gallons.
40 X 7.5=300 GU's. Then divide the GU's by the end of boil target volume of 6 gallons.
300/6=50 or a specific gravity of 1.050. It's critical to get accurate volumes when making these calcs. A half gallon either way makes a pretty big difference. ie. 300/6.5=46 or 1.046. 46/50=.92 or 92% which is an 8% drop in gravity due to the 6.5 gallon ending volume vs 6.0 gallons.

 

[ajf]

I do, just in case something has gone wrong during the mash/sparge, and I could end up with a low OG. That way, I can add some DME or sugar to make up the deficiency. However, I use a refractometer so it only takes a couple drops, and the reading is ready in less than 1 minute. Only once in the last 5 years have I actually added some DME to the boil, and that was because the scale I used was set to pounds and decimals instead of pounds and ounces, but old habits are hard to break.

-a.

 

[D-Ring]

My efficiencies have been all over, but usually high (82% on a 70% recipe) the pre-boil gravity lets me know how much water to add to get my numbers close.

 

[RedGlass]

That makes sense. I was only thinking of it in terms of efficiency, but I definitely see the utility in making sure I hit my target OG. Thanks guys.

 

[AnOldUR]

That makes sense. I was only thinking of it in terms of efficiency . . .

Like everyone is saying, knowing your pre-boil efficiency allows you to make the adjustments needed to end up with the bitterness ratio (ibu/sg) that you anticipated. I think pre-boil is the more important number. Brewhouse efficiency speaks more about commercial breweries making money. Knowing your pre-boil number gives you the best opportunity to make quality beer.