Mash time in high temperature?

H all!

Do i need to increase the mash time to get higher mash eficiency when mashing on temperatures like 68-69 degrees celcius?
I usually mash around 65 degrees, but this time I wanted a really fullbodied porter with high OG and an FG around 1.020.

I found out that Mr eficiency was maybe 10% lower then it used to be with the lower mash temperatures. Do i need to mash for a longer period with the higher temperatures around 69 degrees or is there something else like maybe mash thickness that might be the cause?

Ideas? Cheers

P.s. The porter turned out great. My best to this day, OG 1.026, but for next batch i want to push the ABV to 10% or higher

Efficiency will depend on other factors .. Biggest factor is quality/size of Grain crush.

Mash temperature (if assuming using a single temperature infusion) lower temp 148-150 F will generally produce a drier more attenuated (pending which yeast you use.. also) /higher abv beer. 153-156 F will have more body and a sweeter / more full bodied beer.

Make sure you mash for at least 60 minutes imo.

If you want to produce a 10% beer you need to really get the gravity above 1.060 (this is a big generalization obviously) Do you have beer smith or brewing software? If not you need to get it so you can dial in your recipes... abv... ibu estimates etc.

If you want to get a more full bodied porter next time shoot for a OG 1.050 range and mash at the higher end 154-156F.. Fermentation temps need to be controlled also !

A thinner mash will convert faster and more completely than a thick mash but the biggest influence on efficiency is the milling of the grain. The finer you can mill the grain and still be able to separate the grain from the wort the higher the efficiency. This also affects how fast conversion happens. I find with very finely milled grain the conversion based on the iodine test will happen in less than 5 minutes.

I might need to do my milling a bit finer. Thanks

I have seen no effect on efficiency with different crushes. It converts faster with finer crush, but I've always ended up on target with a (reasonable) coarser crush. If fact. A few batches a go I didn't notice Maris Otter are smaller grains than the default base malt I usually use, lots of grains didn't look crushed, but they were. No drop in expected efficiency. I do recirculation through a HERMS.