Posted Thu May 17, 2012, 6:11pm Subject: Coffee getting bitter in thermos - HUH??
Greetings!
This is my first post here; just joined this week, but have been doing a fair amount of reading on the forum, the reviews & how to's. Thank you for all the information! This looks to be a great forum! I do love my coffee and have just recently been upgrading my equipment.
I made a fatal error though - two variables in a single process. I used a new coffee for a full pot in a new brewer. I ran out of my usual Cafe Altura Organic French Roast and opened up a Cameron's Organic French Roast when the new Cuisinart DCC 2650 arrived.
I take my own brewed coffee to work in a 1 liter Zojrrushi stainless steel thermos. It keeps the coffee hot from 7:30 AM to 4 PM. I pour a cup fresh from the pot for my first morning cup at home and then the rest goes in the thermos and a Starbux stainless steel travel mug. I do not let the coffee sit in the pot on the warmer. As soon as the brew is done I decant it into the various vessels.
The first cup at home is great, the coffee from the travel mug is great and the coffee from the thermos is great as well, until about 10:30. The coffee gets bitter just sitting in the thermos. I've never heard of this. Have you folks?
The thermos is only a week old, so there is no residue built up, its still shiny clean. On the weekends I pour the coffee into a Zojrrushi 1.85 glass thermos for drinking through the day and the coffee flavor is stable, no bitterness over time. The Starbux mug will keep coffee hot for 3 to 4 hours and the coffee doesn't get bitter in that.
I've tried different grinds from the Bistro grinder, but the size of the grind doesn't seem to matter.
Is this event truly related to storing in the stainless steel thermos?? Possibly a problem with the grade of stainless steel?
Any insight or information on this dilemma is greatly appreciated!
Posted Fri May 18, 2012, 6:52am Subject: Re: Coffee getting bitter in thermos - HUH??
Hello Dino, first welcome to CoffeeGeek, its wonderful to have you.
Your experiences don't surprise me. Coffee needs to be prepared fresh and drank fresh. What is most likely happening (and I'm no chemist) is the coffee particles suspended in the coffee are still brewing and this changing the flavors of the coffee. Other components are likely changing too.
The best advice is to brew less and enjoy it sooner. Perhaps look at single cup brewing setups. Myself I have may brewers but even on the weekends brew my own coffee one mug at a time and enjoy it fresh for best flavor.
Sometimes truly good coffee isn't the most convenient.
BrianFoster Senior Member Joined: 1 Apr 2012 Posts: 17 Location: Anoka, MN Expertise: Professional
Espresso: Dalla Corte Evolution,... Grinder: Maestro, Virtuoso Vac Pot: Yama Drip: V60s, Woodneck, Chemex,... Roaster: Primo PRI20
Posted Fri May 18, 2012, 7:09am Subject: Re: Coffee getting bitter in thermos - HUH??
Your experience isn't uncommon. When you brew your coffee, you are extracting a lot of soluble material (caffeine, flavors, etc) from the grounds. A lot of these compounds aren't very stable.
As your coffee is sealed in the thermos, it will begin to stale pretty much from the moment it is brewed. Compounds break down, and produce bitter and burned flavors. I can't find my Cuppers Handbook, so I don't have the specifics in front of me, but it shows the different chemical reactions as coffee stales in hot and cool environments.
There is also a (significant) chance that the coffee may have something to do with the bitter taste. If your coffee isn't fresh (max 2 weeks old for whole bean) and if you are measuring by volume instead of weight (your French Roast will need more volume than a light roast to have the same mass).
Try a different coffee, and measure your dose by weight, and see if that helps.
jkoll42 Senior Member Joined: 2 Jan 2010 Posts: 465 Location: Pennsylvania Expertise: I love coffee
Espresso: VBM DD V3, Gaggia Baby Class Grinder: Cimbali Max Hybrid, Bunn... Drip: Technivorm, Chemex Roaster: Honey Badger 1K, HG/BM
Posted Sun May 20, 2012, 8:45am Subject: Re: Coffee getting bitter in thermos - HUH??
I basically have the exact same routine except I use a Nissan stainless thermos and have no bitterness issues. It sounds like you have fine particles making their way into the brew that are continuing to extract. Are you using paper filters or gold tone? It is also possible that you are sensitive to the slight taste stainless can give to coffee. I need to season the thermos each time I clean with espresso cleaner or I can taste it, others seem to be more sensitive to stainless.
Posted Sun May 20, 2012, 1:19pm Subject: Re: Coffee getting bitter in thermos - HUH??
Thank you for the warm welcome and for your input and interesting information. I did a bit more testing - with a different brand of coffee.
I tried some Altura Organic Dark Roast and it doesn't seem to develop that bitter characteristic after some time in the thermos. Overall, I have found a couple of things wrong with that Cameron's Organic French Roast. The first is the development of bitterness & it takes a significant amount more to equal the bold and full flavor of the Altura beans. Caveat emptor on Amazons Gold Box deals on coffee beans! :-0
I tried both coffee's in both brewers and it isn't the brewer and it doesn't seem to be the thermos. The Cuisinart has a gold metal basket but I still put a paper filter in it to keep the tiny particles out of the pot. The Zojirushi just gets a paper filter.
I don't think I have a sensitivity to the stainless as the Starbux travel mug is stainless inside and there are no issues with that.
As suggested I do suspect that the Cameron's coffee must be having some sort of reaction with the stainless thermos as there is no issue when I store it in the glass thermos.
jkoll42 - I'm curious about your statement that you "need to season the thermos each time I clean . . . " I've never heard of this practice and Googled it but didn't find any info on it. What is that process?
Yes, I would prefer to make my coffee fresh at work but like others noted I cannot have any appliances in our offices. I am considering the purchase of a AeroPress Coffee Maker to use at work. I did try to use my Bodum french press, but found the coffee didn't stay hot enough during the 5-minute soak time.
I think I will start weighing my coffee instead of using the timer on the Bistro grinder as well.
Alas - the search for a good cup of coffee at work continues. ;-)
jkoll42 Senior Member Joined: 2 Jan 2010 Posts: 465 Location: Pennsylvania Expertise: I love coffee
Espresso: VBM DD V3, Gaggia Baby Class Grinder: Cimbali Max Hybrid, Bunn... Drip: Technivorm, Chemex Roaster: Honey Badger 1K, HG/BM
Posted Mon May 21, 2012, 6:06am Subject: Re: Coffee getting bitter in thermos - HUH??
dino92g Said:
jkoll42 - I'm curious about your statement that you "need to season the thermos each time I clean . . . " I've never heard of this practice and Googled it but didn't find any info on it. What is that process?
Not sure if there is an actual technical term and since it reminds me of seasoning cast iron I jus call it that :)
Basically, when I use backflush detergent to clean everything out it does a great job, but first use I can pick up a little off taste from the stainless. After I clean everything I pull out my stash of garbage beans and run a pot. Fill up my stainless stuff and let it sit for a bit. Dump, rinse. It saves me from having a day of 'something tastes a little off with this coffee'
Posted Mon May 21, 2012, 7:52am Subject: Re: Coffee getting bitter in thermos - HUH??
Some people perceive increased acidity as bitterness - it depends on how you "taste" a particular flavor. In general, it's thought that acids are perceived as "sour" and bases (alkalines) are tasted as "bitter", but this is a highly variable term.
WRT coffee, Chlorogenic Acid is present in green coffee, and the amount differs depending on the varietal.
CGA by itself is not perceived as bitter (Journal of Food Science Volume 52, Issue 1, page 213, January 1987), but more importantly is that the heat from roasting decomposes CGA into other compounds that DO taste bitter - mainly caffeic and quinic acid (types of byproducts called "chlorogenic acid lactones").
The temperatures achieved by darker roasting can create another class of compounds (from breakdown of CGA) called "Phenylindanes". These can have a lingering, bitter taste.
So, here's these two compound classes that are known to have a bitter perception. They are created when CGA is subjected to heat. Some of these come from roasting, especially darker roasting.
When you hot brew coffee, CGA that is present that hasn't yet broken down will again begin to decompose. Unless you're making espresso (which by virtue of the higher temperature and pressure produces more phenylindanes), most of these compounds will be quinic and caffeic acid. The longer the coffee is exposed to heat, the more CGA is decomposed into bitter compounds. The byproduct of this (well documented) is the increase in acidity as the coffee is subjected to continuous elevated heat.
These compounds will also change too, and there's a whole host of other aroma and flavor compounds that will degrade, de- and re-compose, and will create "staleness" - which ranges from just nasty to semi-sulphurous to skunklike.
Takeaways from this:
-There's a reason that cold brewed coffee tastes less bitter - since it was not brewed with heat, few of these bitter compounds and acids were produced. The pH is also higher (i.e. less acidic). -Consequently, there may be something to why cold brewed coffee seems to last longer when stored - with lower temperature, not as much CGA has been decomposed, which is more stable than the quinic and caffeic acids, which will go on to create staling compounds... -Brewed coffee stored at elevated temperatures will increase in bitterness. The higher the temperature, the more bitter. The longer the time at high temperature, the more bitter. -There's implications for roasting, and is one of the big reasons for the recent thinking of "stretching" the time from 1C to 2C. Stretch it too far, though, and the coffee becomes "baked", but what this means in chemical terms is the characteristic bitter flavor that gives coffee life in the cup can be almost bypassed altogether - where instead of creating just the right amount of flavor, you skip over the intermediate compounds to less flavorful ones. But roast too quickly and you create larger amounts of bitter compounds.
I've been playing around with percolation methods and cold brewing coffee - I can now achieve technically correct extraction, but the coffee produced is definitely different - I like it but my wife says, "you've given me all kinds of stuff, but the 'coffee' is missing". What I did realize is how UNbitter the stuff is - all kinds of different flavors (amazing from a simple store- bought Eight o Clock) that haven't been at the forefront of the flavor profile with traditional brewing. The more fascinating thing is how much character the cold brewed stuff took on once it was heated to near boiling and it rested for about 25 minutes. I can only think that it's related to these type of chemical changes, but starting with less of these compounds.
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