Ask The Brewmasters

Good afternoon all, 

Does anyone have any recommendations for the best material for gaskets and valve seats for a hot liquor tank that is acidified with Lactic acid to a pH of 5.0 +/- .3?   Usually at a dose around .9-1.25ml per gallon.  We are seeing some of our gaskets and other soft EDPM parts deteriorating more quickly since we switched our HLT additions to Lactic acid from Phosphoric acid.  It's been nice not having to descale the HLT each month but we have found that the black EDPM seats have been eaten away by the passing liquor as recirculates overnight etc. 

1. Has anyone else experienced this problem with Lactic Acid in the HLT?
2. Is this due to EDPM not holding up to the hot Lactic? or do we need a different "cure" or type of EDPM? Is the grey EPDM better in this situation? 
3. Should I be looking to source a different material like Viton for this?  

Now the other part of this problem, a few months back we were doing some CIPs of the HLT and having recently been through an expansion and had to get new tanks ready for production, our head brewer wiped the inside of the HLT with a white rag after rinsing and noticed some black residue on the inside walls of the tank.   How long it's really been there, I have no idea as wiping the insides of 10+ year old tanks hasn't been a regular practice!  My first guesses at what it could be were Carbon from our water filters, or rubber from HxCH gaskets and the 1.5" gaskets and valves.  We then tried to wash the tank with Citric Acid, PWB, Caustic, Nitric all with no change. The inside of the tank looked clean under a flood light but the white rag test would always show something left on the surface. 

Any idea how to remove the surface contamination that won't come off with more aggressive "normal" cip steps?

And lastly, I am guessing this is also due to the acid? We have noticed some discoloring/yellowing of our volume level tube.   - Does anyone know anything we can do to prevent this from happening? 

Thanks for your help! 

Brendan McGinn
Director Of Brewing Operations
Zipline Brewing Co
Lincoln NE

Hi Brendan.  How quickly are these gaskets failing?

I suspect your damage might be due to heat rather than lactic acid, though you are well-within normal heat tolerance for EPDM.  Lactic isn't a great oxidizer; it's a fairly weak acid and EPDM has good resistance to it.  Maybe it's a combined effect, or something else is going on; not sure.  I know from first-hand experience that our EPDM gaskets on hot liquor and hot service water systems (both ~170°F for us) go to mush after something beyond a year, and our water chemistry is such that we don't have anything else in those waters.  Rather than going to Viton or PTFE (which would probably also work), we have implemented a preventative replacement program on critical water systems so that degrading gaskets don't become a sanitation risk.

There are a bunch of chemical/polymer compatibility charts available for reference online.  I've used references from ISM and Trelleborg, but there are many others and all are not necessarily aligned; it's worth checking another resource or leaning into your supplier for an application-specific recommendation.

Related: I wonder what will become of Viton and PTFE in view of current discussions around PFAS... Could get spicy.

Hi Brendan,

I've had good luck with silicone valve seats and tank gaskets, especially for higher temperatures.   Silicone is typically cheaper and more flexible than Viton and has similar properties to EPDM.  I would agree with Jeff that you will still want to replace these regularly once you learn the wear and tear on them, nothing does well in high heat for very long.   I've seen our Viton, Buna, and EPDM gaskets soften and turn to black mush in our hot liquor tank if left in for too long.  This could be the black residue on the tank walls, but I've also seen carbon particulates do that as well.   Hand scrubbing is all we ever found to take it of, maybe others will have better recommendations.   

On your sight glass, I'm not sure what that discoloration is but it could be that the tubing or pex you are using isn't rated for the high temperature it might see, or because the sight tube is cooler than the tank maybe you are precipitating out some minerals or the lactic acid is concentrating there and attacking the plastic.   Just some guesses, not much help in that area I'm afraid.  

Hi Brendan,

It's also possible that you're over-acidifying your water. A pH target of 5.0 is pretty low - and if you keep adding acid until the water is stable at 5.0 with agitation, the target is even lower (depending on your source water composition, if you get to 5.0 with "laminar" water and then vigorously agitate it, it pH could climb back as high as its original value with no acid). I recommend treating your water to a total alkalinity that will eliminate chalk precipitation, such as 50 mg/L as CaCO3 (aka 1 mEq/L), and let the pH fall wherever it ends up. That will probably give you a more predictable impact on mash pH, and you can always add more acid in the mash and kettle on a per-recipe basis to reach your pH targets. If that significantly reduces the amounts of lactic you add to your HLT, maybe your gaskets will last longer without switching materials.

Hi Brendan,

Here is an excerpt from a table of elastomer compatibility with a wide range of chemicals.  This shows that EPDM is recommended for cold lactic acid, but not hot lactic acid (concentration not provided).  Fluoro elastomers, for example Viton, are the best fit of the elastomer types included in this table.

Cheers,

Ashton

Hi Brendon:

I noticed that everyone missed addressing the black "dust" in your HLT.  Most likely this is polishing dust.  Dry polishing of stainless steel with nylon abrasive wheels generates an electrostatically charged dust that clings
tenaciously to the polished surface. The dust is pulverized stainless steel and abrasive consisting of either
aluminum oxide or silicon carbide.  Because of the strong electrostatic forces involved, the black dust cannot be removed with alkaline or acid detergents. Removal requires neutralization of the electrostatic charge. This is best accomplished using a quaternary ammonium chloride-based product or another cationic agent.

You can contact me directly for a product and the procedure to take care of this common problem.

Cheers, 

With equal mash pHs as starting points, the colors of your grains will have a negligible impact on your late runnings pHs. Your mash thickness and target pre-boil gravity are important factors, though. I like using 1 mEq/L as an HLT target because it's low enough to stop chalk precipitation, it's low enough to keep your late runnings pHs reasonable for the vast majority of beers, but it's high enough that having to adjust mash pH upward is rare. The only times I have issues with late runnings pHs are for very low-gravity beers, but you can compensate for that by mashing those beers thin (lower first runnings gravity -> higher late runnings gravity, and the brewhouse efficiency hits are very low for low pre-boil gravities) and - for very low gravities - stopping your sparge early and adding HLT water directly to your kettle to reach your pre-boil volume.

Also, how are you converting dKH to mEq/L? The formula I've used is mEq/L = 0.3574 x dKH, which would result in an untreated alkalinity of 3.43 mEq/L and a treated alkalinity of 0.2 mEq/L in your HLT. To treat 4.42 mEq/L to 0.32 mEq/L instead of treating 3.43 mEq/L to 1 mEq/L, you'll use roughly 73% more lactic acid (assuming the acid is 88 % by wt).

I hope that all makes sense!

Good observation on that black dust, Dirk! I missed that originally or assumed it had to do with gasket failures.  Quats indeed can work wonders for soils such as this.  If the surface can be dried and one has an antistatic pistol at hand, this can be an easy check.  I'd bet one could make enough charge to make a check with a piece of wool and a balloon.  Zap!