Basic Coffee Science
Today, boys and girls, we are going to learn about permeability and membrane walls as they relate to coffee. There is a lot of misconception about the basic laws of science where this is concerned, probably because of the constant misinformation disseminated by roasters or marketers who don't really care about coffee quality as much as they do the flow of moola through the one-way valve, into their bank account.
Coffee beans are a protective shell for the precious oils and sugars inside, which give the coffee its unique and delicious flavor. The oil and sugar inside the coffee bean IS the coffee (this is the stuff I'm paying for). These are stored in tiny pockets inside the bean, and the walls of the coffee bean are a barrier to gases.
Also inside these pockets is carbon dioxide, which helps preserve the oil and gives the coffee aroma. As soon as the coffee has been roasted, the CO2 begins to escape (in coffee, it's termed "degassing"), and is replaced by oxygen. Oxygen is the enemy of oil, and causes it to go rancid. Rancid coffee oil equals stale coffee. This is a continuous process of degassing (staling), and after a period of time, the coffee loses it's unique aroma and tastes noticeably stale in the cup. I don't like to drink coffee over one week old- that's my personal preference.
The shell of the coffee bean is what's known as a semipermeable membrane. It slowly lets CO2 out, and slowly lets O2 in. Nothing can stop this from happening. Well, maybe something can, but probably nothing that wouldn't alter that taste and composition of the coffee. (For instance, I have a theory that using liquid nitrogen to freeze the CO2 inside the bean- dry ice- might halt degassing, but would probably cause the coffee beans to explode). That's why putting them in the freezer doesn't do any good- it has to be REALLY cold to freeze CO2 (-108.4 degrees Fahrenheit).
Putting coffee beans in a heat-sealed bag with a one-way valve on it may keep off-tastes out of the coffee (like when you cook onions or put it in the cupboard with your raw garlic), but it won't even slow down the degassing process. If they're roasted, they're degassing, brother.
Buy it fresh. Use it quick.
That's all I have to say about that.
Coffee beans are a protective shell for the precious oils and sugars inside, which give the coffee its unique and delicious flavor. The oil and sugar inside the coffee bean IS the coffee (this is the stuff I'm paying for). These are stored in tiny pockets inside the bean, and the walls of the coffee bean are a barrier to gases.
Also inside these pockets is carbon dioxide, which helps preserve the oil and gives the coffee aroma. As soon as the coffee has been roasted, the CO2 begins to escape (in coffee, it's termed "degassing"), and is replaced by oxygen. Oxygen is the enemy of oil, and causes it to go rancid. Rancid coffee oil equals stale coffee. This is a continuous process of degassing (staling), and after a period of time, the coffee loses it's unique aroma and tastes noticeably stale in the cup. I don't like to drink coffee over one week old- that's my personal preference.
The shell of the coffee bean is what's known as a semipermeable membrane. It slowly lets CO2 out, and slowly lets O2 in. Nothing can stop this from happening. Well, maybe something can, but probably nothing that wouldn't alter that taste and composition of the coffee. (For instance, I have a theory that using liquid nitrogen to freeze the CO2 inside the bean- dry ice- might halt degassing, but would probably cause the coffee beans to explode). That's why putting them in the freezer doesn't do any good- it has to be REALLY cold to freeze CO2 (-108.4 degrees Fahrenheit).
Putting coffee beans in a heat-sealed bag with a one-way valve on it may keep off-tastes out of the coffee (like when you cook onions or put it in the cupboard with your raw garlic), but it won't even slow down the degassing process. If they're roasted, they're degassing, brother.
Buy it fresh. Use it quick.
That's all I have to say about that.
posted by Brian at 10:27 AM
3 Comments:
Hey, so does storing coffee beans in the refrigerator slow the degassing process at all? (I have heard that it does, although I am too fearful to try it, because I really don't want my coffee to taste like the inside of my refrigerator. But maybe if one had a coffee-only refrigerator... HAHAHAHAHA!)
And do you know why Illy stores/ships its coffee under nitrogen? Your comment about liquid nitrogen made me think of it. They package their coffee in cans, then they extract the air and force nitrogen into the can. I always thought this was so that even though the coffee continues to degas, at least no oxygen is invading the beans. Somehow nitrogen is superior to oxygen in this regard, I guess...? Do you know how?
There was an interview with the head of Illy in the Economist recently, and he listed the innovation of storing coffee under nitrogen as one of 7 major advances in coffee science of the 20th century. !!!! But I can't remember what makes nitrogen so special.
A coffee-only refrigerator, huh? Sounds like a good idea. Fill it with liquid nitrogen.
I am going to have to say no. The temperature of the refrigerator (or the freezer, for that matter) isn't cold enough to stop (or even slow) the escape of carbon dioxide from coffee beans. In fact, chances are, moisture from inside the bean could sweat and condense on the beans and cause them to stale faster. And get yucky.
I have heard a bit about nitrogen flushing, but not enough to know for sure the effects. A new company that is selling espresso from various roasters on their website actually contacted me recently, wanting to sell my espresso. They said they would prefer to vacuum seal and nitrogen flush my coffee beans, in order to preserve the shelf life. When I asked questions about how this worked, they weren't really sure. My guess though, is that all the ambient air inside the bag is nitrogen, so that the carbon dioxide that escapes from the bean is replaced by nitrogen instead of oxygen, and I assume that nitrogen does not cause coffee oils to go rancid. Some questions I have about this method:
When the bag is opened, does the nitrogen escape from the coffee beans immediately, very slowly, faster than carbon dioxide, or what? If the answer is immediately or very rapidly, it is all for naught.
Second, what effect does the nitrogen have on the flavor of the coffee oil and sugar? And what aroma, if any, is carried in the nitrogen? Does nitrogen make crema on espresso like carbon dioxide does? Does it persist as long or longer? Does the flavor change at all?
Lots of questions, not very many answers. Until then, I don't want my coffee sold under this method. Or stale. Roast-package-ship, all in the same day.
It's the freshest coffee on the planet! :)
You've suggested that oxygen entering the bean leads to rancid oil. In that case, the oxygen and oil must be interacting in some kind of chemical reaction (oxidation). Most chemical reactions are sensitive to temperature, including oxidation. The ultimate rate of oxidation depends on the nature and form of the oil, the presence of any antioxidants (natural or otherwise) and other factors.
I don't know much about coffee, but it is routinely recommended that expensive cooking oil be stored at cool temperatures or refrigerated to preserve flavor and avoid rancidity. I would guess that the same is true of coffee oils, in which case refrigerating or freezing (my choice) would definitely help avoid rancidity.
Post a Comment
<< Home