Peated malt late mash addition

You could do this, but you'd risk getting unconverted starches in your wort/beer.

 

Why do you not want to reduce the amount in the grist? It sounds like less phenol character is the goal, so that seems like the obvious approach.

(Attempt to answer my own question)
But perhaps there are some desirable extractable smoky characteristics in peated malt and some undesirable ones, and you are looking for ways to get desirable ones and avoid less desirable ones.

(Running with this answer, in multiple directions)
If that is where you are going, this sounds like a chemistry conundrum suitable for an advance organic chem degree. I don't have one of those. You would need to know more about the different compounds that are contributing to the flavors and the differences in extraction efficiencies over time, etc.

This reminds me of the cold steeping approach with roasted grain. The idea behind it is that you can allegedly extract enough color from the roasted grain without extract the harsh roast characteristics. I say allegedly only because it seems to work for me, but I never did an experiment, with properly measured chemistry and such, and don't want to be accused of confirmation bias. So, two characteristics that can be extracted, color and roast, and using temperature and time to widen differences in extraction efficiency of the two, so that you are extracting the one sufficiently, and the other, not so much. Would it work with desirable and undesirable phenolic characters?

If you have stuck with me this far, perhaps you will want to try that experiment. Hot steep and cold steep some grain and taste the difference. See if you like one more than the other. If cold steep is the winner for you, I would cold steep and throw the liquid in the mash. (Note: I usually cold steep roasted grain overnight if I am going for color without roast; maybe play with different cold steep times)

However, maybe adding a late addition of peated malt to your mash will do the trick too. Vikeman mentioned that it won't have much time to convert, but I am assuming that you are not using a whole lot of peated malt and the unconverted starch would be pretty insubstantial. If this is still a concern, you could also put the peated malt in a grain sock at the start of your mash, and pull the sock out after a short time. You would extract some of the peated character, also some starch, but the starch would have time to convert.

 

I've never had this beer and never tried to darken a beer through extended boiling, so I am not offering up any first hand experiences. It is not clear to me if you are concerned about the color, the flavor, or both. Either way, I would look to the recipe and make sure you are close to the clone recipes out there online. Maybe compare the various online recipes and make sure you are not using some outlier recipe that comes up short on specialty malts. You probably did this already.

Although I haven't had HOTD Adam, I recall first learning of the this beer via the Mad Fermentationist blog years ago, and he boiled for 3.5 hours. That beer came out looking quite dark (first tasting notes here) but that color still probably is mostly derived from recipe rather than the wort darkening via extended boil. The first link shows the recipe he is using. It has 4 oz of chocolate and 2 oz of black malt in a 3.5 gallon batch. It doesn't specify brands or color for these malts, and the calculated SRM is 27. In Beersmith, I recreated the recipe with a 500 SRM chocolate and a 600 SRM black malt and got to 27 SRM. (Note -- the MF says he used somewhat less peated malt than the recipe called for and said that his beer is less smoky than the original).

If you are convinced your recipe is not the issue, then maybe it is the boil. If you are loathe to boil for 3.5 hours, perhaps you can use the old "Scottish Ale" homebrewer trick of boiling down 1 gallon of first runnings, also discussed in a Mad Fermentationist blog post. That should not lengthen your brew day as much and apparently does impact the complexity of flavor (and the method apparently may be conducted in one brewery in Scotland, Traquair house). Again, the disclaimer -- I have no experience with the technique. It may or may not get you closer to where you want to be.

 

I'm not familiar with the beer in question. But my question to you would be, how have your attempts so far compared with the original? i.e. what differences do you (or others) detect?

But in general, yes, a longer boil will result in more Maillard products, i.e. Melanoidins (color) and lots of not very well cataloged compounds that can affect flavor. A longer boil can enhance "malty" flavors. If that's what's missing, maybe a touch of Melanoidin Malt, Dark Munich, or Belgian Aromatic might help. A longer boil can also enhance "caramelly" flavors, so maybe a bit of Crystal/Caramel 40 would help. (Again, I don't know the beer you're cloning or the goal.) Or if it's just color that's lacking, a small amount of dehusked Carafa (Carafa Special) or even Sinamar might be the ticket.