Low Last Runnings

[JMBrewer]

I am having a really hard time getting my final runnings above 2 plato. Right now, they come in at 1 plato. The wort doesn't taste asstringent, but I need to get this resolved.

We formulate our recipes on a 91% effeciency with Promash. We collect 17.5 barrels to boil down to 16. We hit our pre-boil gravities and our post boil gravities, but why are my last runnings so low? We used to collect to 18.5 to boil down to 16.5 with a 90 minute boil. I thought we were obviously over collecting so I reduced the boil to a 75 minute and collected a barrel less.

We used to collect in just an hour, but I quickly made it a two hour run-off.

The mill settings are pretty good. I'll be addressing one little issue later, but it doesn't have much impact on the mash.

We adjust our grain bill based on the analysis from our malt supplier. We are using 660# 2-row with 110# caramunich 40, plus another 55# of carastan malt.

I will be brewing the second half of the batch tomorrow and could really use the help.

Thanks,
James

[JMBrewer]

I meant 605# of 2-row.

[zachjenny]

If your hitting your gravities fine, why don't you just stop running off when the wort drops to 2-2.5P, then top off the remaining volume in the kettle with water? This way, you'd still hit your gravity while reducing the chance of extracting tannins.

[jwalts]

Hey James, does your refractometer or hydrometer correct for temperature? Is it properly calibrated? I'm one of those "measuring last runnings gravity is just an indirect way to measure last runnings pH" people, so I think you should check the pH directly. If it's under 6.0 at room temperature, you're probably ok.

Joe

[jwalts]

I just thought of something else - how's your liquor-to-grist ratio during the mash? Increasing your volume of mash water (and therefore decreasing your volume of sparge water) will result in higher-gravity last runnings.

Joe

[gitchegumee]

91% brewhouse efficiency might be low. You could have channeling in your grain bed. To avoid this, I stir the top half of the grain bed every ten minutes during the mash and then take the mash temperature to assure myself that the profile is right. If I don't stir the bed, then I'll get a shrunken, broken "cookie" in the mash tun. And then of course low yields, and low PRO gravity. Try to force the sparge through the entire grain bed evenly. BTW, we get about 95% in a 10bbl tun. Good luck!