[musseldoc]

I starting adding a 1/4 tsp of DAP at knockout as a source of yeast nutrient.  However, the batches where I have done this have turned out considerably darker (maybe 3-4 SRM) than expected.  Additionally, I can wort using a pressure cooker (15PSI @15 min) to have sterile wort on hand for yeast starters.  On one batch I added DAP before canning and the wort turned out mahogany in color, which is strange considering I only used domestic 2-row to make the starter wort.  I know that DAP is used to darken belgian candy sugar while you are heating it, and I am wondering if the dark color I am observing is coming from the same effect.  Am I on the right track and will adding DAP while the wort is still hot cause darkening?  Any other thoughts?

[erockrph]

DAP is a nitrogen source, so maybe this is leading to increased Maillard reactions? Just a WAG...

[noblesquirrel]

There's plenty of FAN in malt, it really isn't doing much except making the beer darker in this instance. If you're concerned about yeast nutrition, I'd use the Wyeast beer nutrient. Personally, I don't think adding 1/4tsp of DAP is doing anything to help out fermentation.

[musseldoc]

Off topic, but why wouldn't DAP help the fermentation?  It is sold as a fermentation aid.  Wyeast nutrient contains DAP.  Fermail K contains DAP. 

[erockrph]

Off topic, but why wouldn't DAP help the fermentation?  It is sold as a fermentation aid.  Wyeast nutrient contains DAP.  Fermail K contains DAP.

DAP is just a FAN source. It is really useful in something like a mead where there is very little nutrient in the fermentables. In beer, the malt will typically provide all the nitrogen that is needed, and then some. It may be useful in something like a Light Lager, where you have a large amount of adjuncts, but even then you're probably fine just with what's coming from the malt.

I doubt DAP is going to cause issues in small amounts, but I don't think that particular nutrient is all that important in a typical beer fermentation.

[musseldoc]

DAP = Diammonium phosphate
FAN = Free amino nitrogen (although a very limited amount of the BJCP study materials incorrectly have it listed as free available nitrogen, you won't see this used incorrectly in the brewing literature or texts.)

There are no amino acids nor small peptides in DAP, just simple nitrogen and phosphorous building blocks that the yeast use to make their own amino acids and ATP.  Again, since nutrient formulas are already utilizing DAP, why is the claim being made that DAP isn't helping the fermentation?

[noblesquirrel]

DAP = Diammonium phosphate
FAN = Free amino nitrogen (although a very limited amount of the BJCP study materials incorrectly have it listed as free available nitrogen, you won't see this used incorrectly in the brewing literature or texts.)

There are no amino acids nor small peptides in DAP, just simple nitrogen and phosphorous building blocks that the yeast use to make their own amino acids and ATP.  Again, since nutrient formulas are already utilizing DAP, why is the claim being made that DAP isn't helping the fermentation?

It's not so much that it's not helping, it's more that it's just adding more nitrogen. Personally, I don't think you need the available nitrogen source unless force fermenting, as in a starter. Perhaps it is useful in a high gravity beer. As to the mentioned nutrients, they do have dap, but it's a very small percentage of what is in the products. There's actual strong evidence in support of foregoing DAP in mead fermentation (Fermaid O), though I haven't pulled the trigger on experimenting with it.

[musseldoc]

DAP is harmful to desiccated yeast cells during the rehydration process (concentration dependent), so it is removed in nutrient formulas (e.g., GoFerm) where you will be making a starter from or pitching with dry yeast (as is mostly the case with mead).  Once the yeast are hydrated and they can regulate through their cell wall, DAP simply allows the cells to make amino acids that are either missing or at low concentrations in wort.  I'm curious what strong evidence are you referencing?

[musseldoc]

Related to the OP, I decided to go ahead and compared it for myself.  I took a single batch of wort (~1.060) and split it three ways.  I boiled each split for 5 mins, then transferred to a canning jar and put it in the fridge to cool.  This closely simulates a flameout addition, starting a whirlpool, then turning on the water to the chiller on my system at home.  One was just wort, one got DAP and one got Fermaid K (which claims to have DAP).  Take a look for yourself and then read which is which below.






In the picture, the jar on the left is plain wort.  The middle one is wort with Fermaid K added.  The one on the right is wort with DAP added.  Even with just 5 minutes of boil time, the ones containing DAP appear darker to me, and I don't see much difference between the Fermaid K and pure DAP (if anything the pure DAP is slightly more red hued).  I think this explains most of the darkening in my wort, especially with my starter wort.  With the starter wort, it gets heated all the way to ~250F (under 15 PSI in cooker) which takes about 15 min, holds there for 15 minutes, then takes about an hour to get down to a temp where I can take them out.  That is a lot of time for DAP to darken the wort.   I also think there is enough time to darken wort even if tossed in with the whirlflock at 15 min and/or at flameout.  The above difference looks to me like 2, maybe 3 SRM difference. 

[erockrph]

Interesting. I wonder if this is pH-related, or if there's a chemical reaction going on that is causing this.