Fly Sparging With Low OG beers

Beerandgranite

I have recently started fly sparing with very good results in mash efficiency (72% to 88% allegedly). I brewed a Bock and Helles bock both with an OG over 1060 with no issues.
However, this weekend I brewed a german pils (og of 1048), and noticed that really early into the fly sparge that the runnings from the mash tun were incredibly clear. I did not account for this and with a bit of research in the moment, I quickly learned that you don't want your running to fall below 1010 due to tannin extraction. I stopped the fly sprage and checked the runnings, and sure enough they were at 1011, and was 1.25 gallons short of my pre boil volume.
I havent been able to wrap my head around how to correct this. a few ideas:
the error was in my recipe design. should I over build the grain bill and dilute in the kettle to reach target OG?the error was in my mash and sparge volumes (1.5qt/lb mash thickness). Would a thicker mash be a solution to this?Fly sparging may not be appropriate for low OG beers ? the problem is possibly overstated and cant be avoidedHow do you fly sparge when brewing low OG beers while preventing runnings from falling below 1010 and still hitting your target pre boil volume?

VikeMan

Acidify your sparge water (to roughly the same pH as the mash) and you won't have to worry about extracting excess tannins.

Beerandgranite

I see, tannis are only extracted when running fall below and 1010 and the ph is high? i am also using RO water (assuming ph of 7), any recommendation on the best way to acidify?

VikeMan

It's not really about the gravity per se. And there is no magic cutoff that eliminates tannin extraction. Tannins are a normal product of every mash. Too much tannins is where astringency becomes a problem.
The hotter the sparge, the more tannins are extracted. The higher the pH, the more tannins are extracted. The lowering of the gravity as the sparge progresses is the result of the wort being diluted by the (higher pH) water, thus also raising the pH of the runnings.
All that said, if you sparge with good RO water, you don't need to worry about it. It has almost no buffering capacity, so it won't shift the pH of your runnings noticeably.

Beerandgranite

I see, while i am using RO water, i put the entire volume in the HLT (strike and sparge) and add mineral additions. does this increase the RO water's buffering capacity when it comes time to sparge? it would seem I need to deepen my understanding of subject.

VikeMan

It depends on what minerals you added. For example, CaCl2, CaSO4, MgCl2, MgSO4, and NaCl won't increase the buffering capacity. But CaCO3, NaHCO3, and Ca(OH)2 will increase the buffering capacity.

TheMadKing

Decrease your mash thicknesses. It will result in less sparge water needed.
Alternatively you could sparge faster and reduce your lauter efficiency intentionally.
I fully support everything Vikeman said and I never experienced astringency issues doing as he advised. But even with properly acidified sparge water I had a reocurring issue with haze formation in my low OG beers. I eventually concluded it was due to over sparging. I have decreased my mash thickness to 2 or even 2.5 qt/lb resulting in much less sparge water which seems to have solved my issue.
This is purely anecdotal and based on observations, I haven't researched the chemistry to back it up though.

Red-over-White

Most of my brews are 1.038-1.046 and I kinda split the difference on the great advice given above. With acidified sparge water, I shoot for low 70's ending kettle efficiency and it almost doesn't fail to hit the mark on volume and gravity. Slow sparge for 30 minutes and then a fast sparge at the end. I use less overall water than most 3V systems do, but it just works.

Bramling-Cross

TheMadKing is right on (as is VikeMan). I've found that keeping my sparge water at half or, ideally, less than half of my entire water budget helps to avoid problems with lower gravity beers. Utilizing a looser mash is a great way to do this. It also creates a larger thermal mass, which helps with heat retention and there's also a school of thought (that I subscribe to) that argues that looser mashes make for more fermentable worts, all things being equal. This used to be a topic of lively debate, not sure if it still is.
Since you're brewing German stuff, use this as an opportunity to do some infusion step mashing. I'm a big fan of the Hochkurz mash, it's a simple step mash program that is easy to perform via infusions on average strength beers and it does a great job at gobbling up your sparge budget.
Lastly, there's no rule that says you have to sparge. Assuming your tun has the necessary volume, I've found that no-sparge mashes produce excellent results for truly low gravity stuff, like Ordinary Bitters, Milds, etc.

Red-over-White

I just ran my numbers on the back of a napkin and I use on average 36% of my total liquor in the sparge. Which works good on my working man strength beers. I typically average ½ gallon left in the mashtun as I ramp to boil.

MicroMickey

I hate to say it but it's like having a nearly empty tank and speeding to the gas station before you run out.
VikeMan is right. Pay attention to the pH of the sparge water. Tannin extraction mainly occurs when the pH goes above 5.9 - 6.0. No matter what your mash pH is, as the buffers in the mash are rinsed out by the sparge water, the pH will rise.