Beer Flavor Stability

 Download complete article, Flavor stability in home brewing! By Tuur Mertens

Tuur Mertens a doctoral student from the Technical University of Berlin has been conducting research on improving beer flavor stability by removal of transition metals. He wanted to give something back to the brewing community and sent us this introductory article on beer flavor stability and how to keep beer fresh. This article touches on all aspects of flavor stability and gives some great tips that are easy for every brewer to implement, regardless of experience level or equipment. Below is a link to his complete article along with our curated summary of his work.

Quicklinks:

5 easy steps to improve your beer flavor stability!

More! advanced ways to improve beer flavor stability!

Controversial topics on improving beer shelf life & stability

Flavor stability in homebrewing

Curated by MoreBeer!

Beer drinkers the world over know the joy of drinking fresh beer ideally from the source. Once beer is packaged and travels, its flavor and aroma starts to degrade from what the brewer intended. Big corporations spend thousands of dollars and hours researching ways to preserve and stabilize the flavor of their packaged beer. As homebrewers we have the luxury of enjoying our beer at its freshest point. But we can’t always polish off a batch of fresh IPA during its peak point. Below are some easy to do and some more advanced methods we can implement at home covered in Tuur Mertens' article on Flavor Stability in Home Brewing.

Easy to do steps

Limiting Storage Time (drink it fresh!)

• Be sure to label your beers with a "packaged on" date and drink the older beers first. Use the good old FIFO: method First-In, First-Out.
• Also be sure to keep in mind that some beer styles don't age as well as others (e.g. hoppy beers, pilsners).

Storing dark and cold

• One of the most important things a brewer can do to maintain freshness is protect the beer from any damaging (ultraviolet AND visible) light; mainly the sun or fluorescent lamps.
• Try and store your beer cold! This is hands down one of the most effective ways to keep your beer tasting fresh! If you're familiar with the Arrhenius equation it will tell you that a temperature rise (or drop) of 10 °C roughly equates to a doubling (or halving) of the reaction rate.

Limiting oxygen downstream (cold side)

• Avoid unnecessary transferring of your beer, and when you do, move it gently and avoid splashing. Try and push with CO2 if you can. Also, it’s best to purge any vessel (bottles, carboys, kegs, etc.) with CO2 prior to filling
• Use high quality bottle caps when bottling. The liner material of the cap can make a big difference, as some allow for more oxygen ingress than others. 
• Another way to keep oxygen out is dipping the capped end of the bottle in melted wax or paraffin. Not to mention that it looks pretty darn cool and it's a perfect way to seal that barley Wine up for aging!
• Consider kegging your beer, as it's a lot less prone to oxidative ageing. This is due to the headspace-to-beer volume ratio, which is much lower in a keg compared to a bottle.
• If looking for a small format package, consider canning your beer. It has the advantage of having absolutely no oxygen ingress after sealing.
• No matter the container type, be sure to store it upright and try to keep vibration and transportation to a minimum. This cuts down on the chance for the surface to interact with the oxygen-containing headspace, slowing down possible oxidation.

Using healthy, vigorous yeast

• Yeast not only makes beer; it also does a great job in cleaning up aldehydes and scavenging detrimental transition metals (More! on that later).They also help keep beer fresh for longer by producing sulfur dioxide (SO2) during fermentation and by lowering the level of free amino acids and dissolved oxygen.
• One easy way improve yeast performance is by adding a yeast nutrient and oxygenating the wort (but only when cold!).
• Ferment your beer at the recommended temperature and pitch enough fresh yeast. You can do this by making a yeast starter. When using dry yeast, rehydrate before pitching.

Limiting heat load during brewing

• Temperature is a big driving force behind most chemical reactions, including those involved in the formation of off-flavors, like Maillard and Strecker degradation reactions. More heat load when brewing can equate to more free radicals and other reactive entities. This equates to more oxidation and further off-flavor formation (e.g. aldehydes).
• Avoid excessively long boils. Its best practice to perform a “rolling” boil, which ensures all necessary boiling requirements are well met within an hour. Not only does a rolling boil help achieve clearer wort, it also helps with hop utilization and lowering levels of dimethyl sulfide (DMS). Be sure not to cover the boiling wort: even though it might help speed up the process, it will hinder DMS and aldehyde removal.
• Try not to mash below 62 °C (143.6 °F), starting the mash at this temperature and above will make sure lipoxygenase (LOX) is largely inhibited. This will benefit the flavor stability over time greatly. Another way to limit lipoxygenase activity is to use LOX-less barley malt.

More challenging steps

Avoiding transition metals

• The metals iron, copper and manganese all promote oxidative (Fenton and Haber-Weiss) reactions in both wort and finished beer. This goes hand in hand with the formation of aged flavor compounds (which come across as cardboard, papery and sherry). and the deterioration of wanted compounds associated with freshness, like hop aromas.
• Try and prevent your beer from picking up traces of iron, copper and manganese. They can emanate from various sources, like untreated water or by using improper brewing equipment, such as Fe- or Cu-containing kettles, pipes, etc...
• Dry hopping can introduce large amounts of manganese and oxygen! So, try and dry hop while yeast is still active to help clean up these compounds.
• You can lower the active transition metal content when brewing by adding chelating agents / chelators. Some examples of chelators that are successfully being used are tannic acid and ellagic acid.
• Another way to lower the amount of metals is to not over-acidify your mash. A mash of 5.2 pH will cause a much higher leaching of iron, manganese and copper from the malt.

Lower relevance or controversial steps

Limiting oxygen upstream (hot side)

Regardless if you believe hot side aeration is relevant or not, you shouldn't go splashing around hot wort or mash liquor. Primarily it's hazardous; and secondly, mash oxidation will occur very rapidly at high temperatures. Hot side aeration may also cause some of the following things:

• Darken your wort and the final beer, because of polyphenol oxidation. This will lower the antioxidative potential thus the flavor stability overall.
• It can promote enzymatic oxidation (lipoxygenase).
• Cause your wort to appear cloudy.
• Cause other indirect flavor changes.

Here are some examples of how diminished HSA can benefit your brewing process and beer:

• Lowered crosslinking of proteins via disulfide bridges, which results in the following:

1. A faster and better lautering, due to increased beta-glucan breakdown.
2. A higher overall attenuation, because of better lautering and less starch & malt endosperm becoming coated with protein.
3. Less oxidation, due to less formations of hydrogen peroxide (H2O2, a very potent oxidizer)
4. Improved proteolysis and amylolysis (breakdown of proteins and conversion of starch into sugar, respectively)

• Lowered polyphenol oxidation, thus creating lighter wort/beer since oxidized polyphenols are colorants.
• Lowered unsaturated fatty acid oxidation which leads to less aldehydes, both enzymatically via lipoxygenase and non-enzymatically from radical-induced autoxidation.
• Less astringency in your finished beer due to less proanthocyanidin oxidation.

Aside from not splashing around your hot wort some other examples of limiting upstream oxygen are:

• Wet milling or blanketing the malt mill with inert gas like nitrogen or carbon dioxide.
• Deaerating your brewing water by boiling it. This will also help remove the chlorine. Win, win!
• Filling your mash tun and boiling kettle from the bottom.
• Using a mash cap to create an oxygen barrier during mashing and avoiding turbulence during transfer or stirring.

Adding antioxidants

Beer is naturally rich in antioxidants that help block oxidation. Some examples are:

• Polyphenols that scavenge free radicals & reactive oxygen species. They also inhibit lipoxygenase and chelate transition metals.
• Melanoidins that scavenge reactive oxygen species.
• Sulfur dioxide and other sulfites that scavenge free radicals and bind carbonyl compounds.
• Chelators that chelate transition metals, like phytic acid, amino acids and melanoidins.

Oxidative mechanisms are immensely complex. That is the reason why "adding antioxidants" is listed under controversial steps. Whether a chemical entity behaves anti- or pro-oxidant really depends on the type and the concentration of that compound, the oxidation state and the pH, as well as the type and concentration of transition metals present, the matrix, etc. That said, adding small levels of sulfite (such as potassium metabisulfite, another well-known antioxidant) will bind carbonyl compounds, eliminating many of the “stale” notes in finished beer.

Bottle conditioning

One reason bottle conditioning benefits shelf-life is because the active yeast will absorb small amounts of dissolved oxygen remaining in the beer. However contrary to popular belief, it will only marginally remove any headspace and/or ingressing oxygen. Active yeast will also reduce several aldehyes to alcohols, making them less flavor-active, and it will assimilate residual free amino acids, 

The reason why bottle condtioning is cateforized as controversial is because it also comes with certain stability risks. One being that, after the re-fermentation phase, your beer will remain in contact with the yeast during storage. This can sometimes result in the yeast dying, especially if stored in harsh conditions which causes the cell contents to spill out into the beer, known as "yeast autolysis".

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