Brewing with Potassium Metabisulphate and Potassium Sorbate

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Perhaps it was during a Basic Brewing Radio episode,  maybe it was a wine making class I took at Brooklyn Homebrew, or simply having a roommate that is a sommelier, but treating beer like wine is an approach that i have been interested in using for the better part of a year.  In wine production, sometimes after fermentation is complete, chemicals like Potassium Metabisulphate (KMS)(K2S2O5) and Potassium Sorbate (C6H7KO2) are used to not only stabilize wine, but also to slow oxidation.  If anyone that you know is allergic to Sulfites, their trouble with wine is caused from this practice.
The purpose of adding KMS is to add self life to wine, since this treatment kills off lots of microorganisms, but it also slows the process of oxidation, which is tremendously important when aging wine for decades.  Potassium Sorbate stops yeast replication, so even after treatment, fermentation can continue, but the yeast do not reproduce and they eventually die.
For my first step into this technique, I brewed a basic wheat beer.  Once fermentation was done, I then treated 2.5 gallons of the batch with both KMS and Potassium Sorbate.  I made a chunky puree of fresh cherry’s from the corner store with about 2 lbs of Cherries and 2 cups of white sugar.  The puree went into both batches of beer.  The treated beer ended up with a Final Gravity of 1.014, while the untreated beer finished off at 1.011.  To treat the 2.5 gallon batch, I used 3/4 teaspoon of KMS and 2.5 teaspoons of Potassium Sorbate

Untreated (left) vs Treated (right)

Tasting of Treated vs Untreated:

Untreated:

appearance: a hazy pink that has a very white head.  There is almost an orange hue to the pink

nose: A very light scent of wheat with undertones of cherry

flavor: very light in flavor, a slight hop bitterness slips into a dry finish of wheat and cherry.

mouth feel: nice and balanced with a light body, the head does leave quickly but the carbonation is medium

overall: very pleasant summer beer.  The balance of the wheat and cherry works really well and the dry finish.  7.5/ 10

treated:

appearance: the head stays around longer than the untreated beer.  Color is identical

nose: Very similar to the untreated beer, but a very very slight chemical scent is at the end of the nose

Flavor:  that’s definitely sweeter than the untreated. The white sugar sweetness removes the dryness from this beer completely.  The wheat character is also faded.  The Cherry perception is increased.

mouthfeel: a rounder body with that chemical taste that is nearly undetectable. Medium bodied and the carbonation seems higher.

overall:  This worked better than I thought it would, the white sugar and the slight chemical flavor really brought out the carbonation and the cherry flavor.  Next time I will use a different sweetener and less chemicals, but this was a worthwhile endeavor.  This opens up very many possibilities!!!!

This process definitely worked, but it needs a lot of tinkering to make beer that is truly outstanding.  Luckily, I learned a whole lot about this process on my recent visit to Sam Adams. The end product I am hoping to make is a fruit beer that actually tastes sweet enough to be considered a dessert beer, but one that tastes very similar to the fruit used.  This could also really help in my cider, which I have yet to be fully satisfied.  Much more to come.

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2 responses »

  1. what was the real purpose of this experiment? prevent oxidation or to see if preservatives can be used without altering the taste?

    • hey David, sorry for the delayed response. I was exploring Belgium! The point of this is to make a sweet desert beer that doesn’t have any chemical flavor and to have complete control over the level of sweetness in the beer. Cheers!

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