Cold Liquor set temperature?

[CharlosCarlies]

Hopefully not too basic/stupid...couldn't find much on it.

We've just been just setting our CLT to ~38F, but I got to wondering if we should be putting more thought into this from an overall efficiency stand-point. We are going to produce a lager, so ~1/3 of the time we'll be knocking out at ~50F and the other 2/3 should be 60-65F.

Thanks in advance!

[brewmaster 2011]

Well with very little info you have given, I would play with your set up try to knock out 2*c below what you ferment temp will be and. try to do it in 45 min.

[CharlosCarlies]

Yeah, I realized I didn't give many details. Really just looking more for basic guidelines on how to approach it and what the pros/cons are of going warmer/colder. I have some ideas, but just wanted throw it out there for people smarter than myself!

[gitchegumee]

I think you should be...

...spending more time thinking about efficiencies. Need to know your heat exchanger data. A good heat exchanger will cool wort to around 5F of the cold liquor. So, if you're knocking out at 60F, then you would be wasting energy to cool your cold liquor any more than 55F (assuming a properly designed heat exchanger). You also would be wasting energy if you recover hot liquor at less than about 176F. Pay to cool water too much and you'll have to pay again to heat it to strike/lauter temperature. Spend some time playing with the liquor temperatures and see how much you can avoid using cooling and heating liquors. Your energy bill should reflect the thought you put into it! Cheers!

[lhall]

The colder your cold liquor temperature, the faster you will be able to knock out. That's a consideration with lighter lagers and increased levels of DMS from residence time in the kettle after the boil.

With a well designed heat exchanger, the exit temperature of your hot water will be around 170 F. For a given cold water flow rate, you will have to slow down your wort flow rate the warmer the cold water is. If your cold water is too warm, you will overflow the hot liquor tank and waste hot water, while having excessive knockout times that might increase the DMS in your beer.

The equation is this for a plate HX:

M(hot) x Delta T(hot) = M(cold) x Delta T(cold)

For your example, assume that the cold water flow rate M(cold) is constant. Assume your Delta T(hot) is constant too - your inlet wort temp and your outlet wort temp. Then you can see that as the Delta T(cold) gets smaller (i.e. you raise the inlet cold water temperature), then the wort flow rate M(hot) would have to decrease too.

Assuming you are doing multiple batches a day and time is money, you will want to knock out as fast as possible. Adjust your cold liquor temperature down until you can't knock out any faster.

[CharlosCarlies]

Really appreciate the detailed (and highly informative) responses guys. That's why I love this forum!