Tuesday, September 4, 2012

Do you skim off the foam as your wort comes to a boil?

Nathan in action, skimming the wort for one of our soleras.
No - 77%
Yes - 22%

When I announced this poll a month ago on both my Twitter and Facebook, I received a few confused reactions along the lines of “Why would anyone skim the foam as their wort comes to a boil?” Despite less than a quarter of homebrewers responding that they do, I think there are a few advantages that are enough to justify this small/optional brew-day chore.

The more protein the wort contains, the more foam forms on the surface of the wort as the temperature approaches 212F (wheat beers tend to produce an especially dense mousse-like foam). While some people refer to the foam as “hot break,” traditionally/technically this term refers exclusively to the flocks of protein seen floating in the boiling wort (for a good picture of what this looks like, see my batch of spelt saison). I’m sure the Germans have some cool word for the foam, but it hasn’t been given a special name by American homebrewers.

Skimming reduces the chance of a wort boil-over in two ways. First, removing the coagulated protein foam reduces the sudden rise at the onset of the boil that within seconds can lead to wort bellowing over the sides of the kettle and onto your burner. Skimming also forces you to stick around the kettle as the wort comes to a boil, so you’ll be there to turn down the heat if necessary. Alternatively you could add an anti-foam product like Fermcap-S (which I don’t care for) or use a spray bottle of water to deflate the foam.

The result of skimming the foam as my lambic wort came to a boil.
Skimming removes break material that would eventually settle out in the kettle or fermentor. You’ll also skim any bits of husk/grain that make it passed your grain filter-bed. Not a big deal if you do a good vorlauf, but it is especially valuable if you BIAB (brew in a bag) or if you cannot recirculate. While no professional breweries that I am aware of skim, their brewing systems are much more efficient than most homebrewing rigs when it comes to getting clear wort into the fermentor.

Skimming does not have a negative impact on the head retention of the finished beer in my experience. This is because proteins are only capable of coagulating one time (Don't believe me? Try to return a hard boiled egg white to its uncoagulated liquid state.) so the proteins you scoop from the wort would not have assisted in head formation. However, if you use a mesh strainer that serves double-duty for anything other than skimming wort, then make sure it is scrupulously cleaned because it doesn’t take much oil to seriously disrupt head stability.

I don’t skim every single batch. For example, when I add first-wort hops skimming would remove the hops before the boil. This rule also serves for any batch where a solid ingredient is added to the wort post-mash, but pre-boil. Otherwise I’m a skimmer (unless someone posts a good counter-argument in the comments).

17 comments:

Adam said...

I tried skimming, but I gave up. Now I just turn the burner down when I see it coming up. If I miss the foaming because my back is turned or I'm away when the boil starts, then I clean up a little mess.

Anonymous said...

Why don't you like foam reducing tools like fermcap-s?

The Mad Fermentationist (Mike) said...

Part of my objection to anti-foam is philosophical, I'd rather do a little extra work than add a synthetic chemical to my beer. The other reason is practical, the FDA suggests filtering any beer made with a Fermcap-S to remove it, and I don't filter.

Duke said...

Hey Mike, it was my understanding that foam control settles out into the yeast cake and isn't present in the finished beer.

Regardless, I wanted to get your take on the head retention and krausen relating to blowing off during fermentation. I've read and been taught in my beer class (yes they have that at Cal Poly Pomona) that blowing off the krausen removes important head-retaining proteins and (I'm blanking, sorry) other stuff.

The Mad Fermentationist (Mike) said...

I’ve been doing some research trying to find the actual FDA regulation, and it does seem that the active ingredient in Fermcap-S (dimethylpolysiloxane) only has a requirement of less than 10 PPM There is no requirement that beers using it must be filtered.

If a drop is about 1/20 of a ml, and Fermcap-S suggests two drops per gallon (3,785 ml), and each drop is 10% dimethylpolysiloxane (the MSDS for Fermcap-S doesn't list the percentage, but another anti-foamer does) then even if none of it settled out you’d be under 3 PPM. Doesn’t change my resistance to using it, but it does make me feel better about drinking beers brewed with it.

It seems like the filtration requirement that was cited may have been for silicon dioxide (which Fermcap-S doesn’t contain as far as I can tell, although Biofine Clear does).

I’m not sure if there is harm from a blow-off, I haven’t noticed an improvement in head retention of my beers since switching from 6 gallon Better Bottles to 8 gallon buckets for primary fermentation. I know anecdotally some brewers claim that blowing off removes some harsher tasting compounds, but I haven’t noticed that either. Plenty of traditional brewers top-cropped their yeast, which would be pretty similar to blowing-off.

John Evens said...

I think my objection is neatly captured in the picture in this post. There you are, spoon in one hand, cup in the other. What happens if the boil does start to get out of control and you can't scoop/stir quickly enough to avoid the boil over? I prefer to be at the ready with spoon in one hand (making sure some clear space remains on the surface of the wort) and the other hand on the regulator so I can kill the heat if needs be.

Chris said...

I'm an extract/PM brewer still, so a little less inclined to skim since I wouldn't want to scoop any still-undissovled DME.

I'm also in a pretty small pot, so I do use fermcap, but I find that ~2 drops in a 5gal batch is plenty, and then none into the fermenter.

andrew said...

Without having the chance to empirically test, I've been juggling the idea that retaining the proteins (no skim) possibly improves the effectiveness of irish moss clinging to negatively charged sulfate groups that supposedly interact with suspended proteins. If fining agents just make smaller molecules aggregate into larger particles then larger existing particles might improve "clumping" (Newton's law) and subsequently dropping out?

Kai Troester said...

I don’t skim. I even boil 26 l in a 28 l pot. This gives me a bit more than an inch headroom and I rarely have a boil-over. Key is attending the pot when it comes to a boil and keep the flame low. It also seems to help when the bittering hops are added shortly before the boil starts.

I’m also one who advocates blowing off the Kraeusen during fermentation. My experience, anecdotal and from a side-by-side experiment (http://braukaiser.com/blog/blog/2010/02/14/should-the-kraeusen-fall-back-into-the-beer/), has shown a harsher hop bitterness when the kraeusen gunks falls back into the beer. I have not evaluated the blow-off’s effect of head retention, though.

As for skimming, a home brewer once mentioned to me that he gets better beer clarity when he doesn’t skim the foam. My only explanation at the time was that the larger amount of protein leads to better break formation. I.e. larger clumps do a better job in gobbling up the denatured protein. I don’t have anything to support this theory and there was no controlled experiment either.

Kai

graymoment said...

I use Fermcap, but mostly for worry free boils and to increase head retention. I may experiment with not using it to see if I see any differences. If anyone is interested, below is the URL to the World Health Organization paper on it. It seems they did several short and long-term studies on it several decades ago and found no sign of health related issues in animals or humans.
http://www.inchem.org/documents/jecfa/jecmono/v06je42.htm

Derek said...

I try to avoid fermcap in the boil, but I'll never make another starter without one. Too many stovetop volcanoes to go without it.

Derek said...

I also skim, but mostly so I have something to do while I'm standing there waiting (forever) for a watched pot to boil.

danger said...

the man who uncooked an egg :)

http://observer.guardian.co.uk/foodmonthly/futureoffood/story/0,,1969723,00.html

The Mad Fermentationist (Mike) said...

I won't be adding sodium borohydride to me beer either!

Aaron Ouellette said...

I decided to try this last batch, what had me thinking was the soup comment. I always skim soup, stocks, and other things where scum rises to the top.

I 100% agree on skipping the anti foaming agents I don't see the need, of course I brew 6 gallon batches in a 10.5 g pot, so boil over would require significant level of inattention.

Chad Middlesworth said...

Great blog, mahalo. I have always skimmed. I do 25 all grain gallons and pull some really skanky scum out of the kettle. I was just looking around to see why I have done it for the past 15 years but there really doesn't seem to be a definitive answer. I always knew I was removing protein. I skim my mead too. I will keep skimming. Aloha

ole jacob helland said...

hei
I quit skimming after once skimming all through a 90 minutes boil. The beer, a galaxy pale ale, ended up with a sodalike foam disepering in seconds leaving the "beer" looking and tasting like grape soda.

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