Slime, dextran, etc

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Slime, dextran, etc

Postby isaaca on Mon Jan 26, 2015 7:34 pm

Hi,

I recently bottled batches of root beer and ginger beer that had been aging (read: forgotten) in my fridge for ~2-3 months. They were pretty thick and the texture was not so enjoyable. I found many other people having the same problem, and it sounds like the problem is production of dextran, a complex long chain of glucose molecules.

From what I've found, the production of dextran is due to some particular straigs of microbes, specifically Leuconostoc mesenteroides, L. dextranicum, L. citrovorum, Betacoccus vermiform, Phytomonas tumefaciens, Streptococcus bovis, and Lactobacillus brevis. All of these are present in most vegetables and starters.

How to fix this? I have two ideas so far. First, the pre-emtive strategie. From this report http://www.biotechnologie-kempe.de/Molasses_OLBRICH.pdf (around page 89), you can see that dextran is a problem in molasses production as well. The molasses becomes very thick and this gums up the machinery. The article notes that dextran can only be produced from sucrose (a molecule of glucose stuck to one of fructose), but not from glucose or fructose themselves. Indeed, I've noticed that many reports of dextran production is based on using sugar or beets as the food for fermentation (not, e.g., honey or corn syrup). Perhaps using some of the following will prevent dextran from forming:
  • honey is mostly a mixture of glucose and fructose (not linked into sucrose)
  • corn syrup is also a mix of glucose and fructose
  • invert sugar is a 1:1 mix of glucose and fructose. You can make invert sugar by cooking sugar with a little water and acid for a while (see, e.g., http://www.chefeddy.com/2009/11/invert-sugar/)
  • pure glucose (you can buy glucose syrup and dextrose powder, both are the same chemical)
  • pure fructose (you can buy this on amazon etc, sometimes called "fruit sugar")
  • another simple sweetener, e.g. galactose (seems hard to find commercially), maltose (malted barley syrup or brown rice syrup), or lactose (milk sugar, looks like you can buy it at home brew stores).
I have yet to try these options, but I would definitely like to do an experiment with a few different ones.

My second idea is an ex-post-facto cure possibility. This patent http://www.google.de/patents/US2686778 discusses a method for extracting dextran from a wort (from making beer). The goal there is to actually use the dextran, but perhaps a similar process would allow you to fix a slimy batch of ginger beer. Basically, the patent claims that adding calcium hydroxide to the beer helps separate out the dextran from the rest of the liquid. The patent suggests doing this by adding calcuim chloride (the salt used on roads to melt ice, though presumably a purer version suitable for consumption!) and sodium hydroxide or potassium hydroxide (very strong bases; sodium hydroxide is lye, used in soap making). When CaCl and NaOH or KOH are added, they will react and form calcium hydroxide (Ca(OH)2), which is what we want. Another option which I think should work just as well is adding calcium hydroxide directly, which you can buy as "pickling lime" or "cal" (in Latin-American groceries). It is used to make pickles crispy and to make corn more digestible by turning it into masa (the process is called nixtamalization). I have not tried this yet, but from the patent it looks like the dextran will become much thicker and you should be able to strain it out or pour off the thinner liquid.

So, to summerize
  • Option 1: use an alternative sweetener like honey, invert sugar, corn syrup, or a malt syrup.
  • Option 2: mix some calcium hydroxide ("pickling lime" or "cal") into the slimy mess and try to separate the dextran.

I have yet to try these options, as I am currently relocating and do not have regular use of a kitchen for a few weeks. Feel free to try these out and I'd love to hear what the results are!

Isaac
isaaca
 
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