settle an argument on mash out

Gentlemen help me out here,my brew partner and i take turns calling the shots on a brew day. my turn,my recipe, im the boss. on his turn he is the boss. we usually agree on everything except  the mashout or lack of one.  we use a gravity fed system. typical batch is 15gal,  that being said , when we  fly sparge (usually about 45 minutes) i use 168-170 degree water.  he uses between 180 up to 200 degree water depending on ambient  conditions.we never have lautering issues either way. our effieciency is about the same it seems.  never noticed any huge off flavors ..,,,,we think. my fear is scalding water on top of the grain bed leaching out tannins.maybe subtle but maybe preventing the perfect beer.i get his logic in raising the grain bed temp but at what risk if any .the water does not immediately penetrate deep into the bed to raise the temp ,in the meantime scalding water is sitting on top. if we had a rims or herms system i would agree on getting the grain bed temp at a unified mashout temp,.but until then im stickin with 168. ANY INSIGHT would help with braggin rights for our next session  thanks ,.,,,,and happy brewing

Do you raise the temperature of the mash before sparging?

since we are using a gravity feed system ,we add the water until we have about 2 inches on top of the grain bed and then we begin to drain .inflow matches outflow.that is my concern the 2 inches of water hotter than 170degrees sitting on top for the duration of the sparge.

How much of the grain is actually heated above 170? Have you probed it with a thermometer? If only a small fraction of the total is heated above 170, I wouldn't be concerned. If you're heating all the grain to 180, that's a different story.

My understanding of mash-out is that you have to raise the temp of the ENTIRE grain bed. Adding the 180-200º water and then stirring the whole grain bed will do that. Then you sparge with regular temp water.

Do an A/B sampling of your beers with each method and decide based on that.

For bragging rights, though... I use your method.

The advice from the experts like Jamil Z, John P, Charlie Bamforth, and classic brewing texts is that water above 180 F will extract undesirable tannin flavors from the husks of the grain.  The extraction occurs at the point of contact.  Any grain husk that is raised above 180 will begin to extract these tannins, the amount of extraction per husk will be proportional to temperature (higher temp = more tannins).  It does NOT require that the entire grain bed be elevated.  However, the more of the grain bed that is elevated the more tannins will be extracted. 

This tannin extraction is also a function of gravity, and pH.  The lower the gravity of the water surrounding the husk the more tannins will be extracted.  Further, the higher the pH, again the more tannins that will be extracted.  Note that pH and gravity are closely related, in that the lower the gravity the higher the pH will rise.  The exact relationship between pH and gravity is a function of grist (darker grains tend to help keep the pH down), and water composition (higher Carbonate levels will raise the pH more quickly for the same grist). 

The 200F water will raise the top of the grain bed above 180F almost instantly.  Further, as the water drains into the grain bed it will raise more and more of the bed above 180F.  How much ultimately gets elevated above 180F depends on the ratio of sparge to mash water.  But, I would guess that, at least, 1/3rd of the bed ultimately would be above 180F. 

So, the magnitude of the tannin extraction and therefore the taste perceptibility of it depends on:

1.  Your specific recipe (lighter beers will be more susceptible)
2.  Your specific water profile (high carbonate beers will be more susceptible)
3.  Your sparge to mash water ratio (a higher percentage of sparge water will be more suceptible)

So, if you were trying to make a kolsch, with high carbonate water (>50ppm as CaCO3), and 3:1 sparge:mash water with 200F sparge water I think you would end up with a beer that didn't taste good at all.

On the other hand, if you are making a robust imperial porter, I doubt you would be able to tell a difference.

To be able to tell with any two beers you should do blind ABA taste tests.  2 of one beer and 1 of the other.  If you can consistently pick out the "single" beer, several times in a row...then there is probably a difference.  If several people can do the same thing...then there is very likely a difference.  AB testing is easily susceptible to bias.

In the end, you are right.  But, how much it matters is a question answered by the above.

argument settled then .thanks for the detailed explaination.makes sense why we cant percieve huge off flavors ,in that most of our beers are over 1.060 and water chemistry is good. Thanks again.

I've done both.

Currently I do a single decoction (remove a third of the mash, bring it to a full boil, and mix it back in) to raise the mash to 165 or so, then sparge with 170 degree water.

I used to just sparge the 150 degree mash with 180-200 degree water.

The major difference I've found is that my current method results in a higher brewhouse efficiency.

If there were any off flavors as a result of the hot water, nobody noticed.