From Pre-Boil to O.G. Problems

[ontum]

Hello,

I am having a hard time finding where I am losing efficiency between my pre-boil gravity and original gravity.

In Short
Yesterday I brewed an IIPA with a pre-boil gravity of 1.054 at 8.1 gallons. After a 90 minute boil I had 6 gallons at 1.064. Beersmith says I should have 1.072 after boil with 6 gallons and this is what I was shooting for. I also used the formula of pre-boil Gravity = OG*(post-boil Volumn)/(Pre-boil Volumn). This gave me 72*6/8= 54. Which is what my pre-boil was.

Why was my OG not 1.072?

Longer Story
I planned an all grain IIPA with 15 pounds of grain and 12oz corn sugar. I was aiming for 1.072 OG and 6 gallon. On brew day I realized I was short a couple pounds of two row, so I supplemented some DME that I had laying around for starters. I compleated the mash and sparge and arrived at my pre-boil vomumn. I added the DME and corn suger according to the recipe and arrived at 1.054, which was spot on to where beersmith said I should be.

Into the carboy I only had 5 gallons because of loss to the 9 oz of hops in the boil and in the lines and heat exchanger. I had 8.1 gallons in the kettle preboil at around 150° and 6 gallons after boil at 65°. I used my calibrated refractometer to measure gravity multiple times. On pre-boil measurements I stirred the wort around and then checked to arrive at 1,054. On post boil, I checked while transferring to to the carboy, as I would turn off the pump and let a couple drops hit the refractometer. I checked with this method three times at about the middle of the transfer.

Am I missing something? Why wasn't my O.G. 1.072?

 

[cmoewes]

Unless you had a big boil over (and lost volume and gravity points) 8 gallons of 1.054 should boil down to 5 gallons 1.073.

How are you taking your reading? Are you using a refractometer or a hydrometer?

The only thing that would explain it would be a bad reading. Maybe not letting the solution cool down enough?

Even a .06 different in your pre-boil gravity reading would result in the the final original gravity you got.

8.1G @ 1.048 => 6G @ 1.064

 

[uncleleon]

If It's not efficiency. When did you add solid sugars? If you just dump them in they can hit the bottom and scorch and not get into solution? Temperature too can play tricks on measurement. Using refractometer or hydrometer?

Measure twice, cut once. I'm sure it will be a kickass ipA either way

 

[Gavin C]

I have questioned Beersmith on preboil measures and started a thread asking about it here. https://www.homebrewtalk.com/f36/me...cy-beersmith-preboil-wort-temperature-508196/

The sample for gravity is at 60 or 68F depending on your hydrometer but the volume measure is taken at whatever temperature the wort is at. If this were cooled to that of the sample the pre-boil volume would reduce.

This shrinkage is taken into account in calculating water volume requirements for the final kettle volume but I don't know if this correction is automatically made in the software for pre-boil volume and pre-boil mash efficiency. Perhaps it is in which case my post is irrelevant.

I don't think that would account for the entire 10 point discrepancy however.

.

 

[cmoewes]

I have questioned Beersmith on preboil measures and started a thread asking about it here. https://www.homebrewtalk.com/f36/me...cy-beersmith-preboil-wort-temperature-508196/

The sample for gravity is at 60 or 68F depending on your hydrometer but the volume measure is taken at whatever temperature the wort is at. If this were cooled to that of the sample the pre-boil volume would reduce.

This shrinkage is taken into account in calculating water volume requirements for the final kettle volume but I don't know if this correction is automatically made in the software for pre-boil volume and pre-boil mash efficiency. Perhaps it is in which case my post is irrelevant.

I don't think that would account for the entire 10 point discrepancy however.

.

I never thought about the expanding/contracting factor... but doesn't beersmith have that coefficient in there somewhere?

Maybe we need to switch all our recipes to strictly weight... we can start calling our carboys 41 pounders instead of 5 gallon :fro:

 

[ontum]

Thank you for the great response.

I use this Ade Advanced Optics Beer Wort and Wine Refractometer

I didn't have any boil over or other unusual loss.

I took the pre-boil gravity readings at several points in the process. I will detail the steps to help give a view of what I did.

1. with 8.1 gallons and no DME or Sugar - 1.041

2. Add 22 oz DME while stirring- 1.049
3. Add 12 oz sugar while stirring - 1.053
4. Add 4 oz sugar while stirring - 1.054

I also took gravity readings after I had drained 4 and 6 gallons into the kettle, but don't have those numbers with me.

Temperature was between 150° - 180° f. The small drops should cool enough to get a good reading after a couple seconds on a refractometer I believe. Is this correct?

The wort certainly expands a bit up the site glass the keg kettle after is heats up, but I wouldn't think it would expand enough to make this big of a difference.

Thank you for all the help,
Craig

 

[feinbera]

Well, those post-fermentable-addition gravity readings look like they're just about where they should be for those weights and eight gallons of wort... drat, I was hoping to chalk your problem up to unevenly-mixed extract.

How are you measuring your volumes? You'd need to be off almost a gallon in total, but a little slop here, a little slop there, maybe counting on previously-observed boil-off rates (then boiling off significantly more/less than usual due to temperature/wind/humidity/mercury being in retrograde/whatever) instead of explicitly measuring both pre- and post-boil volumes? A gallon sounds like a lot, but, a guy could probably get off that much without trying too hard...

 

[Natdavis777]

I dealt with this issue when I first started brewing, but I dont think you are running into the same issue. I was pulling off the top of my BK after I cooled, and the stratification was causing my OG to be the same as my pre boil SG. So When I take samples now, I make sure I get everything nice and stirred up before pulling a same.

Now the most recent issue I have had was my refractometer. I had to ditch it. I compared it on my last brew with my hydrometer and even calibrated both and it was consistantly lower. My hydro was dead on at 60F. Granted my refract was from amazon and was only 30$, it was giving me an efficiency of 74% opposed to my actual 83%. Back to the hydro I go.

 

[ontum]

Well, those post-fermentable-addition gravity readings look like they're just about where they should be for those weights and eight gallons of wort... drat, I was hoping to chalk your problem up to unevenly-mixed extract.

How are you measuring your volumes? You'd need to be off almost a gallon in total, but a little slop here, a little slop there, maybe counting on previously-observed boil-off rates (then boiling off significantly more/less than usual due to temperature/wind/humidity/mercury being in retrograde/whatever) instead of explicitly measuring both pre- and post-boil volumes? A gallon sounds like a lot, but, a guy could probably get off that much without trying too hard...

Good points.

I recently added a new site glass a couple batches ago. I leveled out the kettle and carefully added one gallon at a time and then marked site glass. The final volume and pre-boil volume were both measured in the same kettle and the kettle was leveled out before taking the volume notes.

Something just accorded to be me where some wort went.
I recently started putting hops in one of these.

After I cooled for a little bit I pulled this up and let as much of the wort drain out as I could and then removed it. This would remove some of water because of the hop absobtion. How much do you think 9 oz of hop pellets would adsorb? It didn't look like a gallon.

Even so, wouldn't boiling 90 minutes in a keggle still boil it down to 1.072?

-
Craig

 

[shtoive87]

I've found that at high temps, some of the wort from the drop evaporates and gives me a higher reading than it should. Now I take wort from the pot with a dropper and cool it in ice water before measuring the gravity with my refractometer. Perhaps this in conjunction with the hop absorption caused the miscalculation? Also is there a correction factor for the refractometer? I have to subtract 4% from my readings because it reads maltose and sucrose differently.

 

[Natdavis777]

Good points.

I recently added a new site glass a couple batches ago. I leveled out the kettle and carefully added one gallon at a time and then marked site glass. The final volume and pre-boil volume were both measured in the same kettle and the kettle was leveled out before taking the volume notes.

Something just accorded to be me where some wort went.
I recently started putting hops in one of these.

After I cooled for a little bit I pulled this up and let as much of the wort drain out as I could and then removed it. This would remove some of water because of the hop absobtion. How much do you think 9 oz of hop pellets would adsorb? It didn't look like a gallon.

Even so, wouldn't boiling 90 minutes in a keggle still boil it down to 1.072?

-
Craig

I too recently started using a hop spider identical to yours. I havnt had any issues with volume or my FG. I did have to hold it out of the wort for about 5 min to get it to drain completely. Next time you brew, pull a cup of wort and cool it, then take a hydrometer reading, then out of the hydrometer, compare that to your refractometer. Or boil some sugar in water and you can check it tonight or tomorrow. Your situation sounds identical to what I just experienced

 

[Gavin C]

Make sure if using a refractometer that you calibrate it with distilled water (steam condensate on the lid of a pot of heating water) to read brix 0.0 and SG of 1.000. Easily done with the screw on the top/side model dependent.

Take your sample for the refactometer and let it cool before measuring. The instrument is calibrated to a specific temp (usually 60F)

These are perhaps not important but if you really want to iron out errors you need to start with measurement errors.

Similarly be sure if using hydrometer, calibrate it with distilled water to check for any constant error, cool the sample to the calibration temperature of the instrument prior to reading. (60 or 68F)

I take my volume from the pot directly and cool hydrometer and refractometer samples (takes minutes in the fridge or freezer) to the right temperature.

Double check the sight glass volume readings on your keggle.

Again, none of this may be of use but it is where I would start.