This blog post is a short summary of a 7-year long experiment looking at whether metabisulfite can be used to increase the lifespan of long-aged vintage beers. The full details can be found in the accompanying youtube video, embedded below. This post is just a quick summary of my main findings.
Metabisulfite – a quick intro
Metabisulfite’s are commonly used as preservatives in alcoholic beverages, particularly in wine where it acts as both an antimicrobial and as an antioxidant. Sulfited wines often last much longer, and age more gracefully, than do non-sulfated wines. The issue with using metabisulfite in beer is that the activity of metabisulfite is highly pH dependent. In solution, metabisulfite can take on three forms depending on pH, as shown in the graph to the left.
SO2 is the form of sulfite of interest in wine, as it is antimicrobial and has some antioxidant effects. But it is present in minimal amounts at typical beer pH, leading many to believe that it has no role in beer. As discussed in the video, this isn’t entirely true as we’re not too concerned with the antimicrobial effect in packaged beer. Instead, we’re interested in the antioxidant effects, to which all three ionic forms of metabisulfite can contribute. The science behind this is discussed in depth in the video.
This experiment was simple in design. I brewed a barley wine, bottled half of it with metabisulfite (using 0.6g/20L, or 0.12g/gallon), randomized the bottles, and then sampled the beers
every two weeks over 2.5 years at random intervals over 7 years when life permitted. Once all the beers were consumed, I deblinded the data and made some interesting discoveries! I used a scoring system to rate the bottles, where:
- Score of 1 = immature beer which was overly bitter and lacked aged character.
- Score of 2 = a beer just coming into the drinkable period, where bitterness is in-balance but aged character is still lacking.
- Score of 3 – ambrosia.
- Score of 4 – getting long in the teeth. Starting to be a tad too sweet, some oxidation character is appearing.
- Score of 5 – undrinkable.
What I discovered was quite interesting, as you can see in the graph on the left. Open circles are control beers, solid triangles are metabisulfite-treated beers
Early-on there isn’t much of an effect on the beers – they age at pretty much the same rate. But around the 3-year mark this changes, with the untreated bottles aging much faster than the metabisulfite-treated bottles.
In other words, the beer was ready to drink at the same time – 2 years post-brewing – regardless of whether metabisulfite was added. But the metabisulfite-treated beers could then be enjoyed for nearly 4 years after that point (e.g. up to 6 years after brewing), while the control beers were only enjoyable for 2 years (eg. upto 4 years after brewing).
Even though I didn’t unblind the data until the end, it was obvious by the 4.5 year mark that there were big differences between bottles. Because of that, I’ve adopted this approach for all of my long-aged beers, although I’ve reduced the dose of metabisulfite I add to 0.4g/20L (0.1g/gallon) based on some of the experiments conducted by Brülosophy.