Low Original Gravity readings

[VikeMan]

Generally the total sparge water is more than the mash water.

That would generally be true with double batch sparges. In any case, the most efficient batch sparges are where each running, i.e. first (pre-sparge) running, second running, and third running (if applicable) has the same runoff volume as the others.

 

[Bw1985]

A couple of thoughts...

1. At 160, the alpha amylase should still convert all of the starches. However, the fermentability of your wort will be low so you will end up with a high finished gravity. See chart below from BYO. That said, the mash temp, if accurate, is probably not the reason for your low OG.
2. 13 pounds of grain for a 5 gallon batch should provide adequate fermentables to hit your your OG. 8 gallons of water should be adequate and will leave you with about 6 gallons in the kettle. This suggests about a 72% efficiency which is even low for BIAB. Perhaps during your second batch sparge you are not mixing the grains first, and then channeling all the added sparge water straight through to the mashtun without extracting remaining fermentables?
3. Is your grain bill high in adjuncts, as the diastatic power of your mash may not be high enough to convert all the starches to sugars reducing your efficiency and lowering your OG?

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Wow thanks for all the responses, I truly appreciate it. I think #2 sounds like one of my issues. I think I just dumped all my sparge water in and didn’t even let it soak. So I basically just ran hot water into my boil pot and diluted the heck out of it!

In regards to #3, my grain bill was 6lbs of 2 row, 6lbs of wheat malt, 1/2lb of Munich, 1/2lb of carafoam.

I’ve never batched sparged, but some quick research on it shows that usually two water additions are recommended, each with some waiting period before draining the tun to allow the sugars to dissolve. There’s always a vorlauf step as well for clarification but I don’t know if that has any effect on efficiency. Generally the total sparge water is more than the mash water.

So, if I sparge with 4gal, should I split it in 2gal sparges at 170f and let them sit for a good 20 mins each? I don’t think my mash is problematic, pH looked healthy and it held solidly at 150.5 for an hour.

I never had issues when I used to batch sparge at closer to 180f, but I heard over 175 can strip too many bitter flavors off the grains. Is there any issue going hotter, or should I stay in 170f range?

 

[Bw1985]

Your problem is probably either mash conversion or lauter (sparge) efficiency. To find out which, you need to measure. At the end of your mash, measure the gravity of the wort. Use this spreadsheet http://braukaiser.com/documents/efficiency_calculator.xls to work out your conversion efficiency. It should be over 90%, preferably over 95%. If it's not, you need to mash longer or crush finer (or maybe address water issues). Unfortunately most recipes say 'mash for 60 minutes'. This is poor advice. A BIAB'er with a very fine crush can get full conversion in much less than 60 minutes. A coarse HERMS crush might take 90 minutes. A poor crush might take longer still. The point is that the mash should run for as long as it needs to. Adding a rest at about 162F helps speed up conversion.

If conversion efficiency isn't the issue, it's probably lauter efficiency. Measure the gravity in the boil kettle and multiply it by the volume in the boil kettle, then divide by the total potential gravity points. There are also lots of online calculators that will work it out for you. For a single sparge beer in the 1.050 to 1.060 range, this should be somewhere around 70 to 80% at a rough guess. If it's much lower than that, you must be leaving liquid behind when you drain the mash tun.

If efficiency is good into the boil kettle, your problem must be lost wort after boilling.

Hope this helps.

Based on this equation I think my efficiency is in the 63% range. 1.030 gravity with 6.5gal in the boil pot. Was aiming for 1.056.

 

[bracconiere]

Based on this equation I think my efficiency is in the 63% range. 1.030 gravity with 6.5gal in the boil pot. Was aiming for 1.056.

that would be a pre-boil gravity.....

 

[Holden Caulfield]

So, if I sparge with 4gal, should I split it in 2gal sparges at 170f and let them sit for a good 20 mins each? I don’t think my mash is problematic, pH looked healthy and it held solidly at 150.5 for an hour.

I never had issues when I used to batch sparge at closer to 180f, but I heard over 175 can strip too many bitter flavors off the grains. Is there any issue going hotter, or should I stay in 170f range?

Regarding batch sparging with 4 gals - you can do a single (no split) or double (split) batch sparge. You will get a little bit better efficiency with the double but less than you may think and may not be worth the extra time. Also, your PH climbs as your wort concentration declines so your risk of tannin extraction goes up with a double batch sparge. A few less efficiency % points can easily be made up with just a little bit more grain. In other words, spending a couple of $s more may lead to better beer.

Regarding batch sparging at 180 - not necessary, and potentially detrimental to your wort. 170 is more than adequate to rinse your grains. Above 170 you risk extracting tannins. Interestingly, research has demonstrated that most tannin extraction is due to high PH rather than temperature at sparge temperatures, that said, better safe than sorry.

Agree it's not your mash temperature.

Additional hypotheses to evaluate...

1. As mentioned in another response - your grains may not have been crushed enough.
2. Wheat malt (~50% of your grain bill) has a high PH relative to other base malts, and you have no roasted or crystal malts so unless you are treating your water, you probably have a high PH which will affect conversion and efficiency. Although probably not by the amount you are experiencing. How do you know the PH looked healthy? Even with 0 alkalinity, I would expect your PH to be in the 5.7 to 5.8 range, depending on how low your 2-row ph is, as it can vary quite a bit depending on maltster and origin.
3. Was the wheat malt actually wheat malt or un-malted wheat. Mistakes happen when filling orders. If un-malted wheat, the diastatic power of your mash would be around 50 which may be borderline for converting all that the un-malted wheat in an hour

Last, if you have access to Excel, below is a link to the program I wrote to build recipes. It is designed around how a homebrewer makes beer. It may look complicated but if you start with Brew System Inputs it will help you to think think about how your systems affects final batch size and OG. After this, build a recipe by first creating your "Beer vision" and then build the recipe in the "Grain-Hops Plan". The Execution worksheet will have all the information for brew day. Ignore the other worksheet as they are for building step and decoction mashes and water chemistry. By going through this process you will learn pretty much all there is to know about making good beer. I am happy to answer any questions.

https://www.dropbox.com/s/pc1vjpqre9dzjhz/Buildabeer v6.2 - DB.xlsm?dl=0
Regards,

 

[bwible]

Based on this equation I think my efficiency is in the 63% range. 1.030 gravity with 6.5gal in the boil pot. Was aiming for 1.056.

Its all gravity points. 6.5 gal at 1.030 pre-boil = 6.5 x 30 = 195 total gravity points in the brew. 195 / 5 gallons suggests this would be 1.039 when boiled down to 5 gallons.

I experienced low gravity a few times when I used old grain that had been sitting for awhile, out of a 55lb sack. I hadn’t been brewing for awhile and it sat for maybe a year. Freshness of grain, others said grain crush? Another major cause of missed gravity is dough-balls or pockets of dry grain within the mash bed. Stir, stir, stir when mashing in. Grain that doesn’t get wet and thoroughly mixed in will not give up its sugar. I poo-pooed this idea too, until I found I was actually doing it.

Far as batch sparging, I’ve been doing that for ages and that by itself doesn’t cause a major loss of gravity points. Just do a slow runoff as others mentioned. Do you recirculate at least some of the wort back through the grain bed? That makes a difference. I used to do it manually using pitchers until I got an Anvil pump. Now I use the pump to recirculate, drain when it runs clear then add all my sparge water at once, let sit for a few min then drain slowly again.

 

[bracconiere]

Its all gravity points. 6.5 gal at 1.030 pre-boil = 6.5 x 30 = 195 total gravity points in the brew. 195 / 5 gallons suggests this would be 1.039 when boiled down to 5 gallons.

thanks for the quick math....

edit: it's weird, it even works when done in liters.....

 

[Gnomebrewer]

Based on this equation I think my efficiency is in the 63% range. 1.030 gravity with 6.5gal in the boil pot. Was aiming for 1.056.

Efficiency is the percentage you got out of a theoretical maximum, not a percentage of your target. You had 13lbs of grain. Potential gravity (ppg, or points per pound per gallon) varies for different grains; I'll use 1.036 (36 points) as an average estimate. 13lbs x 36ppg = 468 gravity points. You had 6.5 gal at 1.030, so had 195 points in the boil kettle. 195/468 = 42%. So your mash-lauter efficiency was around 42% using a crude estimate for grain potential. 6.5 gallons at 1.056 would have been 364 points, which is 78% efficiency - a reasonable target for single batch sparge system.

It's apparent from this that your issue is either conversion efficiency (eg. crush) or lauter efficiency (sparge) or a combination. There's nothing you've mentioned about your process that is fundamentally wrong. Your efficiency should be better. Take measurements throughout the brewing process on your next brew to find out where the issue is.

 

[RM-MN]

6lbs of wheat malt

Wheat is smaller and harder than barley so it often does not get crushed well if at all. Without crushing you get very little conversion so you efficiency takes a big hit. If your supplier mixed the grains before crushing they had the mill set too wide to crush wheat malt.

Now that you have had problems with efficiency for more than one batch it is time to get your own mill and get away from the problems of too coarse of a crush. Until you do you are at the mercy of whomever you buy grain from.