[mabrungard]

This is one thing I've always wondered about this method, is dropping that pH too low after adding the dark grains at vorlauf. I subscribe to JZ's thinking in that brewers have been mashing grains all together for centuries, no reason to change it. I doubt Fuller's is adding their dark grains to the London Porter at vorlauf...
I'm using debittered black in an oatmeal stout today, I'm really looking forward to it.

You can't cheat chemistry. While adding roast and crystal malts at the end of the mash helps keep mashing pH in the correct range for most of the enzymatic action, it may result in an overly low wort pH in the kettle.

For beers like Schwartzbier, Dunkel, Irish Dry Stout, I think that the reserving technique is pretty good when you use low alkalinity water like RO. In the case of the Schwartz and Dunkel, the amount of roast is teeny and the technique helps keep the roastiness low. In the case of the Dry Stout, the low wort pH is a signature of the style and the water at the Guinness St James Gate brewery is essentially RO water anyhow. However, you can't use those examples as justification to use the technique for all dark styles. It doesn't work.

The qualifier that you should apply to JZ's comment is that those old brewers where using their local alkaline water to brew the beer that best fit their water source.

Better beer will always be created by those who know how to work with their ingredients...and in some cases, adjusting those ingredients to conform with the beer they water to brew. Being able to adjust water chemistry took brewing out of the age where you could only brew certain beers in your area and made it possible to brew any style.

[brewinhard]

This is one thing I've always wondered about this method, is dropping that pH too low after adding the dark grains at vorlauf. I subscribe to JZ's thinking in that brewers have been mashing grains all together for centuries, no reason to change it. I doubt Fuller's is adding their dark grains to the London Porter at vorlauf...
I'm using debittered black in an oatmeal stout today, I'm really looking forward to it.

You can't cheat chemistry. While adding roast and crystal malts at the end of the mash helps keep mashing pH in the correct range for most of the enzymatic action, it may result in an overly low wort pH in the kettle.

A couple years back (prior to checking my mash pH), I brewed a RIS where I added all the dark roasted grains (quite a bit) at vorlauf. This is exactly what happened.  I think the pH dropped so low in the kettle that the final beer was actually quite tart. A complete dumper after a few keg pours. That was a big waste of money and time.

[BanditBrewers]

I have never done this during the vorlauf but i have put dark malts and cold soaked them adding them to the mash when running over starts. another thought is the way I have done it is on a bigger scale so adding the dark malt later is good for color rather than take