Boil Vigor

I had a question about how "hard" of a wort boil is preferred. I have my kettle on my kitchen stove (gas). Its a 32 qt SS and it sits over two medium sized burners. With the cover on it creates a good rolling boil. My question is this, I was brewing with a friend last weekend, and he thought we should keep the cover on so that the boil was a good hard boil. I tend to keep the cover off, and the boil is much less rolling. I had read that you want the cover off. Is there any problem with a less vigorous boil?

A less vigorous boil will give you less hop utilization (bitterness) but more aroma / flavour. A higher boil will give you more utilization, but less aroma / flavour. Keeping the cover on is a bad idea, as hot wort is producing diacetyl (butter scotch / popcorn taste) which can be nice in some beers (cream ales) but is usually a bad thing, and can become over powering and rancid. Keeping the cover on means the diacetyl is not evaporating and is simply falling back into your pot. It is allways a good idea to boil your wort with the cover off.

just my 2 cents...

Good rolling boil also required in order to coagulate proteins in your wort and create good hot break material. As Kadmium said it also required to get rid of diacetyl, for that boil with 10-15% evaporation rate should be good enough. It means you can have cover partially on as long as you provide correct evaporation rate. And try to avoid condensations from the cover dripping back in to your wort.

Small correction, get rid of DMS, not diacetyl. Diacetil is a product of fermentation.

So long as large bubbles are breaking the surface constantly, you should be fine.

My food science sister inlaw said that a boil is a boil. Vigor with reguards to boil mearly tells you how much liquid you will lose due to evaporation and as stated earlier, hop utilization.

Thank you all for your replies. Glad to hear that the boil does't have to be all that vigourous, because my two burners at full blast with the keetle cover off can't do better.
I guess what I have been struggling with is that my buddy has 25+ years brewing experience and sometimes I find info like this that conflict with his advice and I find myself tip toeing around some things. I guess its a balance. Well, I'm glad to have the advice. And between his advice and my learning, I guess I will work it out.

WormBoy said:

Thank you all for your replies. Glad to hear that the boil does't have to be all that vigourous, because my two burners at full blast with the keetle cover off can't do better.
I guess what I have been struggling with is that my buddy has 25+ years brewing experience and sometimes I find info like this that conflict with his advice and I find myself tip toeing around some things. I guess its a balance. Well, I'm glad to have the advice. And between his advice and my learning, I guess I will work it out.

Click to expand...

That's why I like this board. You can have 25 years of experience, but a practice that could be improved but isn't, is just that- a poor practice, no matter how many times or years you do it.