unintentional protein rest

ugh! so brewing last week and trying to rush mash-in, and somehow misread my thermometer and left my mash at 135 for an hour...realized my mistake decocted ~4.5 quarts of mash to raise the temp to my originally desired 151 for almost another hour.

so...what will the affect be of doing the 135 rest vs. a single infusion at 151? anything? (I realize the decoction will have some affect...I would have just infused more water, but I was absolutely at the max volume for my mash tun (time to upgrade!).

I don't think it will hurt. Generally I do protein rest at 122 for my undermodified stuff, like wheat etc, but all its supposed to do is make sure they get 'surplus diastatic power' if I recall the term, to allow the modified malts to have power to help extract the goods from the non modified malts. In theory all it could do, is add some extra extraction from your grains. So... I think you'll be just fine. 135 may even be out of the range, and then it just means you spent some time in a lower sacc rest range getting different kinds of sugars out. I don't now recall what they were, but there was a lower range that one type of sugars/proteins come out, and a higher one for others, and they meet together in that 145ish to 155ish range most mash at... but I'm definitely cloudy right now on the specifics. Something I read in a book I have. Sorry I'm getting senile. I still think you'll be fine. Now, the one thing you may have done was added some yummy carmelization to the wort w/ your decoction which people love, and decoct on purpose to get .

135F is out of the protein rest stage (113-131F). you were in the beta amylase stage, which will probably result in higher fermentables and less body than the single infusion.

135°F will give activity to both proteolytic enzymes and beta-amylase enzymes. With most malts, an hour at 135°F will probably take a little foam formation/stability out of the beer. For fermentability, rests at those two temps (135°F and 151°F) will probably give a well-attenuated, fairly dry beer.

It would have been better to push the second rest (after realizing the mistake) up to the mid to upper 150s°F... this would have balanced out the fermentable sugars/dextrin ratio. But live and learn... I'm sure your beer will be fine anyway.