Low Gravity During Sparge

[mpkimler]

Hey Everyone,

First off, I would like to say thank you for all of the great advice on these forums. I have used these forums extensively over the last few years to find answers to many of my questions. Such a great resource.

I have looked through the forum for an answer to my current question but to no avail. I apologize if this has been discussed, and if so, please direct me to the proper thread.

I will try to keep this short and simple. Last weekend I was brewing a 10 gal all grain batch of an Oktoberfest clone recipe I found. Below is the recipe I was using:

8.5 lbs Pilsner (2 Row) Ger (2.0 SRM)
5 lbs Vienna Malt (3.5 SRM)
4 lbs Munich Malt - 20L (20.0 SRM)
2 lbs Caramel/Crystal Malt - 20L (20.0 SRM)
1 lbs Aromatic Malt (26.0 SRM)
1 lbs Cara-Pils/Dextrine (2.0 SRM)
1 lbs Caramel/Crystal Malt - 40L (40.0 SRM)
2.0 oz Tettnang [3.9%] - Boil 60 min Hops
1.0 oz Tettnang [3.9%] - Boil 45 min Hops
1.0 oz Tettnang [3.9%] - Boil 30 min Hops
1 pkgs German Ale/Kolsch (White Labs #WLP029)

I mashed at 151 deg F for a little over an hour. I began sparging with 168 deg F water and collected 8 gallons of wort. I then checked the gravity of the wort coming out of the mash tun and it had dropped slightly below 1.01. From what I have read, continuing to sparge at this gravity, you have a higher chance of extracting tannins. The pH had climbed up a little from 5.2 to 5.5. I have never had this issue before so I made the executive decision to stop sparging and added 3.5 gallons of fresh water and used DME to try and get my FG that I was shooting for. After the boil and cooling, I was within a few points of the FG so I was fairly happy.

So why did the gravity drop below 1.01 when I had only collected 8 gallons of worth when I needed 11.5 gallons for boil?

Here a few things that I can think of:
1. Sparging too fast. It took me about 1 hour to collect the 8 gallons.
2. Bad crush on the grain or temp was off so ultimately I didn't get the conversion.
3. Shorted on grain from the brew shop. Not trying to blame them, but it is possible.

I would appreciate any guidance you guys can offer. The three main things I would like to know is 1.) Are there any other reasons my gravity dropped below 1.01 when I collected only 8 gallons of wort? 2.) What are the things you guys look for when making the decision to stop sparging? 3.) What do you do if you don't have enough worth collected after the sparge?

Thanks,
Michael

 

[eltorrente]

There's so many factors involved, so it's probably not possible to say exactly - based on your specific setup and variables.

First of all, if it dropped that low - it was the best thing to just stop the sparge and add top-off water.

Perhaps the particular cooler you were using, combined with the flow of sparge water, caused "channeling" in your grain bed and you didn't get full utilization out of all of your grains, once the flow of sparge water had found it's path through the grains.

One thing I always do is sparge with 180 degree (or more sometimes) sparge water. If your water is at 168, by time it hits the grain bed, it's already cooled down several degrees - plus the grain bed itself will not hit anywhere near 168 anyway, even if your water was exactly 168 coming out of the tube. The hotter it is, the more likely you are to get those sugars out of the grains. Using hotter water won't cause tannins, so don't be concerned about that - but it might give you a few points on your efficiency. When I sparge with 180, my grains only get into the low 160's, anyway - never anywhere near 168 I'd like to get to.

It's possible you had a bad crush on your grains. One of the reasons to buy a grain crusher. You can't always trust that the grains you get from a homebrew shop will be what you want.

 

[hercher]

One other possibility is that your sparge water may have been "channeling" -- that is, not flowing through the grain bed evenly. If you don't properly recirculate your wort before sparging, your sparge water may find easy paths through the grain, and thus you aren't collecting all the sugars. This is often caused by inadequate recirculation or sparging too fast.

That said, 1 hour for a 10 gallon batch seems a little fast to me. When I fly sparge, it takes me about an hour to collect enough for a 5 gallon batch.

 

[rklinck]

Just to be sure, your gravity readings were coming from a refractometer and not a hydrometer? You will never get a good value from a hydrometer even after temp adjustments at sparging temps.

From your descriptions, I am guessing that you did not take a reading on the first runnings alone. That would be helpful to determine whether the problem was from before the sparge or were a result of something in the sparge process.

Did you take a preboil gravity reading? It would be interesting to know how far off you were from expected so that we can get a sense of the efficiency you got overall. I guess we could figure this out if we backed out the DME's contribution.

 

[mpkimler]

Thanks so much for the replies! Lets see if I can respond to all of the things you guys brought up.

1.)Channeling - I will admit that I do not have the best setup. I use a 10 gallon cylindrical cooler for mashing. The return manifold was a design I found online that is pretty simple. I used a single straight piece of silicone tubing with notches cut out every 1/2" or so. This tubing is inside a piece of SS braid that is only used as a filter to keep grain from going into the notches. One end of the tubing is plugged and the other connects to the bulk head. I have been meaning to make something better but it seemed to work ok for me in the past. The other thing I don't have is a good way to evenly distribute the sparge water. I use a pump to pump the sparge water on to the top and I just try to evenly spread it out by moving the hose around the top of the cooler. Nothing fancy.

2.)Sparge Temp - I did periodicaly monitor the temperature of my mash tun while sparging. The hottest I ever saw was 154 deg F and I think it started to drop from there towards the end of the sparge. The small volume of hot water I was adding for sparging had little impact due to the large volume of water in the mash. The point i'm taking from this is that its the temp of the mash that is the concern with extracting tannins, not the temp of the sparge water.

3.)Crush - I do have a mill, but was a little leary of using it since I'm not exactly sure what the crush should look like. I was maybe too trusting of the brew shop. I will take this under advisement.

4.)Recirculation - I did connect the pump up to the cooler before sparging and recirculated the mash tun for about 10 minutes before I started sparging.

5.)Sparge Rate - I think John Palmer reccomends 1 qt/minute. To collect 11 gallons of wort, that would be 44 minutes. I honestly don't know what is right, thats all I was basing it off of. Sounds like I should cut that about in half for a 2 hour sparge rate?

6.)Gravity Reading - I was using a hydrometer to take the reading. One thing I wasn't certain about in regards to the 1.01 rule is if you shoot for 1.01 at actual temperature or referenced back to standard temp? My hydrometer was reading 1.01 at actual temp.

I did not take a gravity reading of the first runnings. I normally do, but forgot this time.

There may not be a point to writing this as its all from memory, but I will give it a shot. My preboil gravity before I added the DME was a 1.04. I also think I took that reading after I added the 3.5 gallons of fresh water. Once boiling, I added 2.5 cups of DME. That was all the DME I had available. At the end of the day, I only collected 9.5 gallons of wort. I think I lost alot more than I anticipated due to boil off and had to leave some in the brew kettle due to hot break. The gravity reading once cooled down to 69 deg F was 1.05.

Thanks again for all the great responses. I think there are several improvements I can make to the brew rig and to my sparging process. Let me know if you guys have any other thoughts.

-Michael

 

[rklinck]

6.)Gravity Reading - I was using a hydrometer to take the reading. One thing I wasn't certain about in regards to the 1.01 rule is if you shoot for 1.01 at actual temperature or referenced back to standard temp? My hydrometer was reading 1.01 at actual temp.

If I understand this right, this is your problem. The 1.010 rule is based on the actual gravity. You would certainly have to correct for temperature, but as many of the experienced posters have pointed out, the adjusted values are pretty far off if the temp of the liquid is above 100 degrees. But if you plug 1.010 at 150 degrees into a calculator, it will tell you that the actual gravity was 1.029. You stopped sparging way too soon.

You really need a refractometer to take these readings. The amount of liquid is so small that it gets to the proper temp in a matter of seconds (I tend to see a change of less than .005) over the course of a minute.

 

[ronjonacron]

I think its 1.010 corrected, you were likely a bit higher than you thought you were, or what the hydro was showing.

Edit- someone beat me to the punch.

 

[mpkimler]

How sweet would you expect the wort to taste at that concentration? I did take a sample of it when my hydrometer was reading 1.01. It didn't have much of a sweet flavor to it, but I guess measuring it is the only way to know. Looks like I need to order a refractometer before I purposely sabotage another batch lol. Thanks again for the help!