Seibel Institute Sensory Seminar – Tasting off flavors in beer

Recently I had the opportunity to attend a tasting seminar and go through the Seibel Institute’s Comprehensive Sensory Training Kit.  The kit contains vials of the chemical compounds that sometimes get into our beer and impart flavors and aromas.  Some are desirable and some are most definitely not desirable… unless you’re trying to make a beer with notes of fecal matter and vomit.

Time to test our senses

Time to test our senses

The kit itself contains 24 vials of pre-measured “standards” representing some of the most common or important flavors and aromas in beer.  The seminar was led by Jamison Jackson, a flavor chemist from Coca Cola.  We used a popular commercial beer known for it’s neutral flavor as our “reference beer” and as a base for the compounds.  Many of them were very faint, and will definitely take practice to discern.  Some were very in your face and once you know what they are you’d be hard pressed to miss them in the future.  It was interesting to note that certain people really picked up on some flavors and aromas that others didn’t but that was flipped for other flavors and aromas.

Seibel Institute's Comprehensive Sensory Training Kit

Seibel Institute – Comprehensive Sensory Training Kit

Here’s a run down of the flavors covered in the kit and my notes on them.  I’ll list the descriptors we were given of each next to the compound name and then give my notes on what I got out of them.  If we didn’t taste one I’ll just list the descriptors and a note that I did not try that one.

Acetaldehyde (Descriptors: Green Apple, Bruised Apple, Latex Paint, Cut Grass)
– Aroma: Faint apple
– Flavor: Unsweetened green apple, grassiness notice in the throat
– Possible Sources: Incomplete fermentation, bacterial contamination, leeching from packaging in PET bottles.  Found in Budweiser.

Acetic Acid (Descriptors: Vinegar, Acidic, Sour)
– Aroma: Salt and vinegar potato chips
– Flavor: Vinegary, sour
– Possible Sources: Naturally produced during fermentation, can be imparted by wild yeasts, bacterial consumption of sugars

Almond / Benzaldehyde (Descriptors: Almond, Cherry, Amaretto, Marzipan)
– Aroma: Almond biscotti and faint cherry
– Flavor: Very faint almond
– Possible Sources: Beer has been stored too long, carryover from other products on bottling lines.  Flavor is easily detectable in Sam Adams Cherry Wheat.

Bitter / Iso-Alpha Acids (Descriptors: Bitter, Quinine)
– Aroma: None
– Flavor: Tonic water, bitterness (like hops with zero aroma or flavor)
– Possible Sources:  Hops adding during boiling, hop extracts.  Over concentration can produce negative results.
– Light can react with Iso-Alpha Acids and Riboflavin (Vitamin B2) to produce skunky odor/flavor in beer.

Butyric (Descriptors: Rancid, Putrid)
– Aroma:  Vomit, definitely vomit. (Butyric acid is one of the main compounds in vomit.)
– Flavor: Rotten meat?
– Possible Sources: Bacteria during wort production or in sugar syrups.  Bacteria in packaging.  Easily confused with Isovaleric Acid.

Caprylic (Descriptors: Goaty, Waxy, Tallowy)
– Aroma: Crayons, unscented candle wax
– Flavor: Like taking a sip of a box of Crayolas.
– Mouthfeel: Waxy, slick. (Not all compounds added a noticeable mouthfeel.)
– Possible Sources: Aging beer during conditioning, produced by yeast autolysis.

DMS / Dimethyl Sulfide (Sweet Corn, Tomato Sauce, Vegetable)
– Aroma: Light vegetable
– Flavor: Light vegetable, corn? (This one was hard for me to pick out.) Rolling Rock is an example of a beer with DMS.
– Possible Sources:  Major source is s-methylmethionone (SMM).  SMM is produced during germination and kilning of malting barley.
– Comments: Two-Row barley produces much less SMM than six-row in the malting process.  SMM is converted to DMS from heating malted grain.  DMS can be greatly reduced using a vigorous boil, however it is important to coil the wort quickly so it does not continue to produce DMS.  Approximately half of the SDMS

Diacetyl (Descriptors: Buttery, Creamy, Butterscotch, Milky)
– Aroma: Unpopped microwave popcorn
– Flavor: Buttery popcorn
– Possible Sources: Natural part of the fermentation process.  Fermenting at low temperatures (such as lagering) can cause Diacetyl, raising temps allows the yeast to consume the diacetyl, this is called a Diacetyl Rest.

Earthy / 2-Ethyl Fenchol (Descriptors: Wet Soil, Dirt)
– Aroma: Like opening a bag of potting soil
– Flavor: A big cup of potting soil
– Possible Sources:  Contamination of water and via migration through packaging by the chemical 2-Ethyl Fenchol.  Normally imparted via tainted groundwater but can also come from post-packaging storage in damp cellars where microbes in the walls of the cellars produce 2-Ethyl Fenchol that migrates through semi-porous packaging into the beer.

Ethyl Acetate (Descriptors: Nail Polish, Acetone, Estery)
– Aroma: Like a nail salon, Acrylic?
– Flavor: Slight flavor or nail polish
– Possible Sources: Natural part of the fermentation process, can be imparted by wild yeasts.  Present in all beer but high-concentrations are undesirable.

Ethyl Hexanoate (Descriptors: Apple, Estery, Anise)
– Aroma: Apple, fruity, perfumey/floral? (Reminded me of a strip club. Don’t judge me.)
– Flavor: Fruit, flowers, anise
– Possible Sources: Produced by yeasts during fermentation.  Can make up a significant part of the character of certain beers but is generally undesirable and high concentrations.

Geraniol (Descriptors: Rose-like, floral)
– Aroma: Citronella, definitely.
– Flavor: Citronella
– Possible Sources: Imparted via hops, important component of hop oil.  Concentration is determined by the type of hop, boil conditions and fermentation conditions.

Grainy / Isobutryaldehyde (Descriptors: Grainy, Green Malt)
– Aroma: Grainy
– Flavor: Faint raw graininess
– Possible Sources: Can be from grains that have not been stored long enough but can be controlled by sparging and wort boiling practices.
– I had a hard time detecting this one but a couple others said this was the most dominant flavor of the night.

Hefeweizen (Descriptors: See Spicy / Eugenol and Isoamyl Acetate)
– We didn’t try this one.

Indole (Descriptors: Farmyard, Fecal, Jasmine)
– Aroma: Smell like a porta potty or RV toilet, a mix of waste and that sanitizer used in those toilets.
– Flavor: Same as aroma, like an RV toilet or porta potty
– Possible Sources: Contamination from coliform bacteria during fermentation, use of adjunct sugar syrups that have been spoiled with bacteria.  DMS is often present with Indole.

Infection (Descriptor: See Diacetyl and Acetic Acid)
– We didn’t try this one

Isoamyl Acetate (Descriptors: Banana, Fruity, Peary, Estery)
– Aroma: Banana Laffy Taffy
– Flavor: Banana Laffy Taffy, without a doubt.
– Possible Sources: Naturally produced by yeast during fermentation.  Can be desirable but will have serious impact at higher levels.  Found in lagers and German wheats.

Isovaleric (Descriptors: Putrid, Cheesy, Sweaty, Old Hops)
– Aroma: Dirty feet, parmesan cheese (very strong)
– Flavor: Very sweaty and cheesy
– Possible Sources: Use of degraded or old hops, excessively high hopping rates.  Can be produced by brettanomyces.

Lactic (Descriptors: Sour milk, Yogurt)
– Aroma: Just like it says… sour milk
– Flavor: Hint of sour milk
– Possible Sources: Contamination by lactobacillus bacteria.

Mercaptan / Ethanethiol (Descriptors: Rotten Vegetables, Drains, Natural Gas)
– Aroma: None?
– Flavor: Perhaps a bit of rotten veg?  Could be contaminant from previous sample.
– Possible Sources: Formed by yeast during fermentation.  High concentrations can be caused by yeast autolysis (or cell death) during maturation of the beer.  Mercaptan is added to propane and natural gas to help detect leaks.
– It was noted from the host that he feels this could have been a bad sample as the aroma should have been more pronounced.

Metallic / Ferrous Sulfate (Descriptors: Inky, Blood, Tin)
– Aroma: Blood, metallic
– Flavor: Blood, pennies… I said PENNIES.
– Possible Sources: Contact with poor quality metal or pipework, can promote stale or oxidized flavors.

Papery / Trans-2-Nonenal (Descriptors: Cardboard, Oxidized)
– Aroma: Not much.
– Flavor: Cardboard, paper
– Possible Sources: Oxidation, usually occurring during storage of finished beer.  Packaging and temperature can have a big impact on this.  Can also be imparted during boil due to pH changes in the wort and the production of Trans-2-Nonenal.  The production of Trans-2-Nonenal is complex and not fully understood.

Spicy / Eugenol (Descriptors: Clove, Allspice)
– Aroma: Phenolic spices
– Flavor: Same.  Clove and allspice as described.
– Possible Sources: Produced during the aging of beers as phenolic compounds.  Desirable in certain Belgian styles but undesirable in others, such as pale lagers.

Vanilla / Vanillin (Descriptors: Ice Cream, Custard, Cream Soda)
– Aroma: Like opening a cream soda
– Flavor: Like drinking a cream soda
– Mouthfeel: Smooth, creamy
– Possible Sources: Produced by the breakdown of barley cell wall materials or phenolic flavor components during aging.

I really enjoyed this seminar and feel like I learned a lot.  I met some other great brewers and a few of us went out for dinner and beers and more tech talk after the seminar.  I highly recommend any brewer or beer enthusiast to take this course if you have a chance.

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