I have not heard of such an experiment with a cup of coffee. My question is what standards would you use to calibrate the HPLC before running the coffee? Also since coffee has hundreds of compounds, the chromatograms could be pretty messy. Last week I read an article by Ernesto Illy (from 2002 I think) and it looked like he used a GC to note several of the main components in coffee. So maybe a GC would be better to evaluate the aging of coffee? With all of the work and time needed to setup this experiment, how many people here would be able to interpret and understand the chromatograms? I do not run an HPLC, but I have access to several of them, although talking my coworkers into several days of a free experimentation might not be easy. I have read articles about how coffee degrades over time but I have never read any that used instrumentation to quantitate it.

Since there are hundreds to thousands of compounds in coffee, one would have to pare down that list to some of the key components that affect taste. Then, determine the elution parameters that would achieve a good separation and resolution. GC would be ideal for many of the aromatic compounds, but HPLC would likely work best for some of the oils and proteins. I would guess that the degradation of oils and aromatics are the primary cause of the stale coffee taste. It would take a lot of experimentation to prove it though.

I think this idea may be approaching the point at which we take the art and joy out of espresso preparation though...

Coffee chemistry is rather complex. There is a body of scholarly research that investigates what substances produce specific flavours and aromas in coffee. One might tentatively assume that the difference between fresh and stale coffee is either a loss of those characteristic substances and/or the development of undesirable substances during the staling process.

There are some 2000 volatile chemicals in roasted coffee but only a few hundred are thought to be easily discernible by the coffee drinker. One substance that has been suggested as a key identifier of roasted coffee freshness is the amount of methanethiol present. (Editors, American Chemical Society 1994). Alkyl pyrazines are also often cited as key aromas in fresh coffee (Grosch 2001). Methanethiol is interesting because it is a desirable component of freshly roasted coffee. But at higher concentrations it actually smells strongly of rotten cabbage or eggs. Below is an example of what was found to be the key 28 flavours in a cup of medium roast Colombian coffee.

A good overview of coffee chemistry in general and how gc/ms is used to study this is Coffee - Recent developments by Clarke & Vitzthum (2001). It's a pricey book but you should be able to find a free, limited preview ebook version of it via Google.

Well why not buy/roast your beans for use, why buy pounds when you use ounces? I have ground my own roasted beans, put in a zip lock bag and froze them. Now 3 moths later I run them in a cheapo brewer, water was hot enough for correct brewing, and the coffee was great, never seem to lose a day. Now this was not a everyday thing, The beans were left for a friend and he didnt use them.

I like your freezing into individual weekend portions idea. When I sold my coffeeshop, I roasted up ten pounds of espresso and divided it into 20 eight ounce one-way valve bags to be immediately frozen. Then I took a bag out each 5-7 days for use. The first bag was as good as the last bag--to my taste.

cannonfodder wrote:I divide up the coffee into pint jars and freeze it. Then I retrieve one jar, dump it in the grinder and go.

This is also what I do. They do make half-pint jars, but a 5 pound bag divided into 15 pint jars sounds like plenty for summer, even if you do have a little extra left over when the weekend is done.

My primary concern with refreezing an open container is condensation. I let the container come up to room temperature before I open it to avoid condensation on the beans. Opening a frozen bag, getting all the beans damp, and then refreezing sounds like a Bad Thing to me.

The experiment has concluded with interesting results! Batch 1 was kept in the freezer until the day of the tasting. Batch 2 was kept in the freezer until a week before the tasting, then left out for a week. Batch 3 was thawed and frozen three times, with a total of 7 days spent out of the freezer. I pulled the shots with as close to the same extraction parameters as possible. Tasting was blind for my friend, but not for me. Multiple shots were pulled and tasted, depending on the amount of coffee in each batch. When taken out of the freezer, jars were allowed to warm up to room temperature before opening in order to reduce condensation on the beans.

Results: My friend, who was blind tasting, correctly identified each of the three batches at the end. The differences between Batches 2 and 3 were subtle, but present. However, there was a great difference between Batch 1 and the other two. Some of the notes that my friend made: Batch 3 was slightly more watery and bitter that Batch 2. Both had a bitter aftertaste. Both characteristic of beans that are going stale. Batch 3 had a creamier mouthfeel and was sweeter.

Conclusions: Multiple freeze thaw cycles seems to have a small, but noticeable, negative effect on the taste of the espresso. Freezing preserved the freshness of the coffee.

My plan: I am going to divide up the coffee I get into small jars that contain enough coffee for the weekend and freeze them. Then, I will take out a jar every weekend. This will prevent any damage from multiple freeze/thaw cycles, and prevent aging while the beans are out of the freezer.



Side note: Has anyone here used roaste.com? Are they legit? How do they offer free shipping from coffee roasters that normally fleece you on shipping?

I'm new at the coffee grinding/brewing/tasting/savouring scene only as a
result of being given the gift of Barista classes through the Canadian
Barista and Coffee Academy this fall 2010. I read the blog on preserving
freshness with great interest as I have yet to purchase good coffee
grinding and brewing equipment, so maintaining the freshness of coffee is
key in my kitchen. One major point that was stressed in these classes is
to NOT refrigerate or freeze coffee/coffee beans for reasons that you
discovered: flavour changes, why? 1. as a result of cooling/freezing and
warming to room temp; 2. odours are absorbed though I think you prevented
that by using the sealed jars yet 3. we were also told that the reason for
the valve in the coffee bean bags is to release the volatile gases that are
emitted as they will also speed the staling process. My understanding from
these classes to just keep what beans you have at room temp, in a dark spot
in the valved bag with the open top rolled down and clamped shut and then
to just grind the beans at time of need. I hope this will be helpful to your
quest for the perfect cup of brew. Have a great day!