Skimming is one of those oldschool ideas that came from a time when brewers were scared of their yeast. They believed that prolonged yeast contact was a bad thing- it contributed to things like the big homebrew Bogeyman, autolysis.
Those ideas are 40 years out of date. Just like Papa Charlie's book......So many views have changed.
There's been a big shift in brewing consciousness in the last few years where many of us believe that yeast is a good thing, and besides just fermenting the beer, that they are fastidious creatures who go back and clean up any by products created by themselves during fermentation, which may lead to off flavors.
Rather than the yeast being the cause of off flavors, it is now looked at by many of us, that they will if left alone actually remove those off flavors, and make for clearer and cleaner tasting beers.
Leaving the yeast alone, and letting the krausen fall through will act like a filter as it sinks, pulling down any proteins and other off flavor causes.
That's why also many of us leave out beers on the yeast cake for 3-4 weeks, and skip secondaries. To let the yeast do their thing.
Like so much of brewing you will find people believing and practicing things they read in books, while others are brewing based on information that is more current. This is an ever evolving hobby, and information and ideas change. And now with places like this with a huuge amount of dedicated and serious brewers, as well as all the podcasts online, you will find the most state of the art brewing info.
Things have changed, we're not so afraid of so called "off flavors" by things that are part of the natural process of the beer production, touching the beer-yeast, trub, spent hops, break matter. Yeast are fastidious creatures, if left to their own devices they will go back and clean up any byproducts that cause off flavors. In fact you find a lot of things that used to freak people out just have proven to be less true. And some processes that were de-riguer back in the day, such as skimming off krausen aren't all that common any more.
It's not like the 60's and 70's (when most of those opinions espoused about autolysis originated from) when our hobby was still illegal, and there wasn't a lot of FRESH yeast available to us. The yeast used in hobby brewing was usually in cake form, which came from Germany and England in hot cargo ships and may have sat on a store shelf for a long time....or the brewer just used bread yeast.
From John Palmer, author of How to brew, on why he changed his opinion about autolysis...
So the whole health and vitality of yeast was different back then compared to now. Back then it made sense. You had weaker yeast that had finished fermentation that were more susceptible to autolysis and breaking down. Now that is not the case. The bar of homebrewing has risen to where we are able to make beer that has the same robustness as professional beer. We've gotten our techniques and understanding of what makes a good fermentation up to that level, so you don't need to transfer the beer off the yeast to avoid autolysis like we used to recommend.
Yeast in the 21st century is much healthier to begin with, and is less prone to have issues like their cells autolysing....just like our own health tends to be better these days.
Now the only ones who really do it are cropping the yeast for harvesting.
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