Grain Fermentation is halting - is it because of PH?

AJW

Hello,
I am attempting to mash-in a 400 gallon grain fermentation of corn, malted barley, and wheat. After mashing, it attains a brix of 15 with a PH level of 5.5. We keep the temperature at 80 degrees and fermentation starts off strong, but halts at around 7 brix with a PH of 3.7 after only 2 days.
I've attempted to bring the PH back up and reactivate fermentation to no avail. Any advice?

Kindred-Spirits

What is your mashing proceedure? Are you certain you are converting all of the complex sugars into simple ones?
pH is on the lower side of of the spectrum for happy yeast, depending on which yeasts you are using.
If you lay out your mashing proceedure I'm sure we can give you some advice if we see something off.

AJW

Thank you for the response!
I start off with 400 gallons of water and add 500 lbs of corn, 150 lbs of red wheat, and 150 lbs of malted barley and begin heating and agitating. At 125°F, I add 1/2 cup of SEBstar HTL and let it work as the temperature rises. Once the mash reaches 190°F, I let it agitate for about 45 minutes before it starts to cool. When it gets down to 170°F, I add 1/2 cup of SEBamyl GL and allow it to work and begin performing starch tests. Once the starch test comes back good, I make sure the PH is 5.5, add 4 cups of Ferm K, and transfer the mash through a heat exchanger to a fermentation tank to cool it to roughly 90°F. Once there, I pitch 1 lb of RedStar Active Dry Distiller's Yeast and set the tank's jacket temperature to 80°F.
We are currently seeing 2-3 days of very active fermentation before it just halts completely, with a brix of 6-7.

Kindred-Spirits

So right off the bat, I wouldn't bring any starches up to 190 except for the corn. By doing so you will denature (Destroy) the natural enzymes in them.
The SEBstar HTL is good, I would keep the corn at 190 to geletanize and then let it cool to about 165-170 and add in your wheat, stir that in well then around 165 add your malted barley.
The range for the SEBaml GL is 30-65C so if you added it at 170 I bet you denatured the enzyme.  I would let it cool and add it in at around 140F.  
I would make a starter for the DADY and pitch when you do at around 90-95F and you should hopefully see some good results.
It seems like you might have gotten the formation of a good amount of complex sugars and some simple sugars in your mash. The simple ones are eaten up over the first few days and then it stalls.
Being that your pH is crashing too you might need to add some CaCO3 (Chalk) to help bring that up and buffer a bit.

Stumpys

I'll second that.
It's not ideal to take all your grain to 190, but you can do it as long as your enzyme additions are sufficient for the amount of starch.  Your problem though, is that you are likely denaturing the glucoamylase by going in at 170f.  Dosing at a lower temperature may result in longer conversion time, but keep in mind that glucoamylase will remain active through fermentation.
In your model, I'd split your high temperature alpha amylase addition in half.  Add half on the way up to 190, add the other half after you've begun cooling, add it back at a slightly lower temp, 170f or so, this way you can start breaking down some of the starches in prep for the glucoamylase.

Kindred-Spirits

Agree with what the others said regarding temp, etc. Some great info there.
We had a similar issue with pH crashing. It's likely due to a bacterial infection. How are you sterilizing your transfer equipment and heat exchanger? Steaming any lines/hoses/heat exchangers is an effective way of doing it. Depending on the pump's design, you may not be able to steam the pump so might want to look at a contact sanitizer or caustic solution.
We thought we were being super clean and ended up finding 2 sources of infection...1. the grist hydrator (perforated ring design). after adding grain, there would be some grain that got in the water ring and turned into fun stuff. 2. dead end in hx piping...the manifold that fed our hx had about a 2" long piece of pipe that extended beyond the final section. It filled up with some pretty cool stuff if you are into dunder pits. haha.
After doing a good hot caustic CIP on everything, we would see yield in the 3.2-3.5 PG/bushel range. Over the course of time, that would drop...in one instance down to 2 PG/bushel. After isolating these issues and addressing them, and being fanatics about temp and pH in the cooking process, we are now running about 4.5 PG/bushel. No matter how clean you think you are being, odds are that if you have a pH crash, it's from acid-forming bacteria inoculating your mash and competing with yeast. Using that PG/bushel metric really helped us dial in our process and understand what impacts changes made to the final yield.
Hope this helps! Cheers! Adam