En av mine favoriter fra Bamforth - video finnes på edX - the sience of brewing.
Du kan lese det han sa - om sulfit kommer lit lenger ned.
Nici
My name is Charlie Bamforth.
I'm a distinguished Professor Emeritus from the University of California Davis. I joined the brewing industry in 1978, the Brewing Research Foundation, spent quite a few years with the Bass Brewing Company and for 20 years was the professor of malting and brewing sciences at UC Davis.
So, what I like to talk to you about is flavor stability, freshness, which is probably the biggest technological challenge facing the brewer today. Because the simple reality is: beer is going to change its flavor. I've lost count of how many different substances contribute to the flavor of beer. It's probably at least a thousand. If you get a detectable change in the contribution of any one of those, then the flavor of the beer has changed and therefore it's gone away from what it should be.
That by very definition is flavor instability.
One of the fundamental questions is: how important is it? There's a lot of stale beer that is drunk across the world, because there is a lot of beer that's being exported and it's traveling vast distances through all sorts of different conditions to arrive at a marketplace and then it is marketed as being a little bit of Belgium, or a little bit of Holland, or a little bit of England, or a little bit of Japan, or something. And frankly, the beer tastes nothing like it did back at home base, because it's aged. So stale beer is not going to kill you. It just isn't what the brewer originally brewed.
So it's a philosophy.
Do you make a thing out of it, do you worry about it? Do you try to do whatever you can to overcome the problem? Or do you just accept it? Like a winemaker would say: 'Why, it's vintage' or 'It's matured' or whatever, it would do. You could say: 'Oh, I've got a, you know, ten year old Pilsner'and celebrate it. - You don't! - 'Oh yes, I do, I paid a phenomenal amount for it, cardboard, delicious!'
So you could tell all sorts of stories. But most self-respecting brewers want their beer to taste just like they expect it to taste. There's a lot of efforts given by many people to keeping the beer fresh. And there are really three fundamental approaches that a brewer can take to maximize the flavor life of the product.
The first of these is to get the oxygen level in the final package as low as possible. If I was giving this talk 10 years ago, I would have had a higher oxygen target than I would now. The bottom line is: the lower the oxygen level, the better. So investment in the packaging facility is critical to try to get the lowest possible oxygen level.
The second thing is: beer in a can basically is going to have a longer shelf life than beer in a bottle. Now, a lot of people psychologically don't like to hear that, because they don't think a can is as classy as a bottle. Now when you fill a can, you can't quite achieve the low oxygen level you do in a bottle. But that is the end of it. No oxygen can get into a can, but oxygen can get into a bottle and it goes in between the neck of the bottle and the crown cork. So progressively, the oxygen level is increasing and that is a prime agent making beer go stale. The tighter the seal, the better.
The second general thing that you can attend to or should attend to is the temperature. There's a guy called Svante Arrhenius, who a long time ago now showed the relationship between temperature and the rate of a chemical reaction.
The simple rule of thumb is: if you increase the temperature of a chemical reaction by 10 °C, then that reaction will go between two and three times faster. Now, there's a lot of beer being shipped around the world and it's being exposed to some fairly ridiculous temperatures It can go through cycles of going up to say 40-43-44 °C for days on end, depending on how it is moved and how rapidly it is moved.
That's not good for flavor stability.
But if you go the other way: it's a great thing: keeping the beer cold! So if you go to 10 °C, we're talking 9 months. (comparing rate of reactions that slow down) Now this is an approximation, but 9 months. And if you're in a refrigerator, refrigerator temperature, you buy a lot of shelf life. There are brewers that are shipping the beer around the world in refrigerated containers. Now it's expensive. There's quite a sizable carbon footprint behind it, but in the interest of keeping beer fresh, it really is the way to go.
The third generality is sulfur dioxide or metabisulfite.
Now it can work in two ways. One is that it actually is a radical scavenger, so it protects against the damaging forms of oxygen. But the second thing is, it grabs hold of the substances that tend to be involved in aged beer, the substances involved in old beer. Many of them contain what is called the carbonyl group:
the C-double bond - O.
Sulfur dioxide will react with that and make what we call an adduct and the beer doesn't taste stale now. In fact, you can take stale beer and treat it with sulfur dioxide and clean it up. Now, over in the States, where I'm based, there's a labeling requirement and you have to put onto the label "contains sulfite'' if there's more than 10 milligrams per liter of sulfur dioxide in that product. So there's a limit to how you can go.
But an old friend of mine from the industry insists that 8 is better than 7, which is better than 6 ppm, which is better than five ppm, so to maximize the SO2 as high has you can, without running the risk of going too high.
So what about these carbonyl compounds: where do they come from? Well, they can come from the breakdown of the bitter acids, so the iso alpha acids. They break down to your carbonyl substances.
Well, people don't like to hear that. because there's not a solution which is: 'Oh well, we'll keep the beer fresh; we'll get rid of the bitterness' - You can't do that! Alright, so they can come from the breakdown of amino acids. Well, that's inconvenient, isn't it? Because we need amino acids to make good beer, because the yeast needs the amino acids. So people don't like to hear about that. So they ignore that.
Alcohols: higher alcohols, like 3-methyl-butanol or propanol or indeed ethanol. They can break down to give carbonyl substances. Well, that's unfortunate, isn't it? Because we need those alcohols, either in terms of alcohol, because it is ethanol but also because they are the precursors of the esters, which are important for flavor. So people don't like to hear that! So they ignore that!
So they all focus on unsaturated fatty acids. Everybody does the research on unsaturated fatty acids. Because unsaturated fatty acids break down to give E-2-nonenal, which is this classic cardboard flavor. They say: 'Well, this is the whole story!' But it isn't! And indeed, you can make E-2-nonenal in other ways as well. You've got different carbonyl compounds that come from other sources and they all react to give E-2-nonenal. So it is not only unsaturated fatty acids.
I will never forget going to a big meeting in Milwaukee once, and they gave me a fancy title, which was 'a critical control point analysis of beer flavor stability' and I said: 'Keep out the oxygen, keep it cold.' 'Are there any questions?'
And people were saying: 'Well, what about the brewers who have invested in brew houses that minimized oxygen uptake?' And I said: 'If you haven't invested in the finest packaging equipment to get the lowest oxygen levels, and if you haven't invested in refrigerated distribution, there's nothing you can do in a brew house. There's nothing you can blame the maltster for that is gonna give you flavor stable beer.'
So with flavor stability, you've got to start at the end and work back. You got to start with the customer really: is the customer being tempted to buy vast amounts of beer because it's really cheap in a supermarket? And then they're buying it and they're storing it under ridiculously warm conditions.
Beer is going stale. So, a lot of science is dedicated to unraveling all of this chemistry, but if you don't get the fundamentals right: looking after the beer and doing the logistics and keeping the oxygen level down and the temperature down in the finished product, there's not no point in worrying about what happens in malting or in the brew house.
You have to decide:
Do I worry about flavor stability? And if you do, then my recommendation is to start at the end and work back. And in terms of what the brewer can do, that is: package the beer with as little oxygen as possible, avoid the presence of things like iron, copper and manganese and ensure, wherever possible, to hold that beer cold right the way through its lifetime.
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