Is starting gravity ...

ill.literate · 03-21-2007, 04:04 PM

more a product of the mash, or of the boil?

Did our first AG this weekend... and our after boil gravity was 1.040. A little low, to me, and according to Beersmith.

I'm thinking it was a product of the mash... which, for AG rooks seems logical to me. But we boiled on our stove, and didn't have a problem reaching a boil, but it wasn't a rolling boil per se.

Just a straightforward red ale ... can post the recipe if wanted.

Thanks!

Evan! · 03-21-2007, 04:20 PM

here's the dilly:

"Starting Gravity" is not a "product" of anything, per se. It's just a number, a reading taken at a certain point. That reading, as you know, is taken after the boil, prior to fermentation, and it measures the amount of sugar that is dissolved in the water. That's it.

Holding the initial wort volume constant (5 gallons for most), the boil has absolutely nothing to do with your gravity. Of course, if you start out with 8 gallons of wort, boil it for 60 minutes, then you'll have boiled out alot of water---but no sugars---meaning your gravity will increase because the sugar/water ratio will increase. But it ALL depends on the volume of the wort.

For example, let's say, pre-boil, that your wort volume is 8 gallons, and you have a specific amount of sugar in that wort, call it X. You boil for 60 minutes and end up with a 5-gallon wort. You take the gravity of that final wort, and it's 1.040.

However, let's say that, instead of starting out with an 8-gallon pre-boil wort volume, it's 5 gallons, but with the same amount of sugar, X. You boil for 60 minutes, end up with 2.5 gallons of wort, then add back 2.5 gallons of fresh water to bring the final volume back to 5 gallons. Your original gravity post-boil should be EXACTLY the same, 1.040.

Long story short, if you're trying to adjust your original gravity, there are two variables that you can adjust: the amount of sugar in your wort (pre- or post-boil), and the amount of water in your post-boil/pre-ferment wort. When doing AG, you increase or decrease the amount of sugar molecules in your wort by adjusting the MASH SCHEDULE and the ingredients therein.

If you feel that your OG was too low, there are two possible culprits: too much water, or not enough sugar. Assuming that you've adequately measured and controlled the amount of water, that leaves the mash...

So what was your mash schedule and your grain bill? Low efficiency can be caused by many things; you should be striving for at least 65-70%, though.

ill.literate · 03-21-2007, 04:34 PM

Evan...

Thank you... fantastic help here! I really appreciate it. I'm at work, so I'm posting this from memory... but here goes.
Recipe :

7 pounds Marris Otter malt
1.5 pounds crystal malt (40L)
1 pound wheat malt
.25 pounds flaked barley
.06 pounds chocolate malt

Mash (as I remember, don't have my notes with me at work)
Single infusion.
Temp of mash in the right neighborhood ... 154, held for an hour in an Xtreme cooler.
Vorlauf, drain.
Sparge water (again, from memory) was around 170. Vorlauf, drain.
Wort yield was around 6.5 gallons or so.

I'm thinking it was the sparge that was the culprit.

casebrew · 03-21-2007, 04:48 PM

Cooled before hydrometer? Hydrometer accuracy? (check it in 68 deg water, should be 1.000)

Otherwise, no where else the sugar could be except left in the mash grist.

And yes, mashing could make low OG, if you really screw it up and leave lots of grain undissolved. You sound good there.

Sparging? Did you stir up the mash after the water addition, and wait a few minutes to soak the sugar out? Leave a lot of sugar in the grist? Did you check the SG of the runnings that were left in the MLT? ( I usually just taste mine, shouldn't be too sweet, but not puckery, like tea.)

ill.literate · 03-21-2007, 04:52 PM

Quote:

Originally Posted by casebrew

Sparging? Did you stir up the mash after the water addition, and wait a few minutes to soak the sugar out? Leave a lot of sugar in the grist? Did you check the SG of the runnings that were left in the MLT? ( I usually just taste mine, shouldn't be too sweet, but not puckery, like tea.)

I think this is where I muffed it.

I forgot to stir it, though I did pour the sparge water in fairly vigorously. I waited, but not too long.

I think that's the case, that there was sugar left in the grist.

Good learning experience, no?

jdoiv · 03-21-2007, 05:24 PM

It's important to gently put the sparge water on top of the grain bed when doing your sparge. Otherwise, you create channels in the mash and will bypass alot of the sugar in the mash. The water just runs through the channels and out into your kettle. I would guess this to be the culprit if you were vigorously adding water at the sparge.

I typically will add water slowly onto my grain bed until I have a good 4-6 inches of water above the grain bed before starting to let the water out into the kettle. I fly sparge, not sure what you sparging process is though.

Just my .02.

**Bobby_M** · 03-21-2007, 05:56 PM

Nah, it sounds like he's batch sparging in which case you stir the hell out of the mash after you infuse the sparge water. No channeling.

ill.literate · 03-21-2007, 06:13 PM

Quote:

Originally Posted by Bobby_M

Nah, it sounds like he's batch sparging in which case you stir the hell out of the mash after you infuse the sparge water. No channeling.

You'd be right... I should have noted, we were batch sparging

Evan! · 03-21-2007, 06:23 PM

Looks like you got about 55% efficiency. Should have been up around 1.055 with that grain bill and a 75% efficiency.

I depart from the method jdoiv recommends, as I batch sparge. I typically add the sparge water, stir for 10 minutes or so to dissolve any remaining sugars, then drain. If you take a hydro reading of the cooled sparge runnings, you should be able to tell whether it's necessary to sparge again. You can also help to dissolve sugars by stirring periodically during the mash, or by doing a stepped mash.

ill.literate · 03-21-2007, 06:27 PM

Well, chalk this one up to inexperience right?

We'll, at worst, have a decent tasting brew, and we'll glean knowledge from this one for future batches.

We've had a hell of a krausen on the red so far, and it's fermenting nicely, so that's encouraging.

Thanks again Evan... as well as the rest of the folks who chimed in.

We'll certainly stir the mash a bit during the first 60 mins, and definitely during the sparge next time.