I am looking for a good, in-depth source on biotransformations (think food science). For example, fermenting black tea and sugar with wild yeast and bacteria (kombucha):

  1. Wild yeast ferment sucrose into ethanol
  2. Bacteria (in the presence of oxygen) convert that ethanol to acetic acid (sours the solution and lowers pH)

This is a transformation of sucrose into acetic acid through the use of yeast and bacteria (but which ones?). Or:

  1. Malting grain causes production of enzymes that later break down starch into sugar
  2. Mashing crushed grain allows starch extraction and conversion (by these enzymes) to (fermentable) sugars such as maltrose, dextrose, sucrose, etc.

I'm interested in what enzymes are produced by which grains, and how they convert starches and in what temperature ranges.

I want to study these types of biotransformations, including how varieties of yeast and bacteria make these transformations (i.e. bacteria converting ethanol to acetic acid only when oxygen is present). This means details on yeast, bacteria, and how they interact with one another in transformations of molecules (thus aromatic/flavor compounds, production of alcohol and acids, etc.).

Is there an authoritative (or close to it) source on the micro-level biotransformations that occur during fermentation? I only know what I know from reading online about brewing kombucha and beer; sources seem to just say "this happens when this", but without explanations as to what is doing what, which is what I want to know more about!

Super bonus points if there's a sort of almanac of common brewing ingredients. For example, breakdown of various malts and their enzyme content, adjuncts such as herbs/spices and their chemical makeup (e.g. linalool, citronellol, etc.), the like. I find the micro-level of fermentation fascinating, and I'd like to finally learn how to balance the bitterness of my hibiscus saison by taking advantage of microbes or a change in the preparation of ingredients/fermentation.

I just found an amazing example of the genre of information I'm looking for on Chemistry.SE. It talks about the use of lemon juice in cooking with fish, and the reason why so many recipes use lemon juice. There is a chemical reason for adding lemon juice, and it's fascinating to see those molecules interact to change a dish. I'd love to have this kind of information, but for beer.

  • What you are looking for does not exist in one location and some of it doesn't exist at all. Fermentation is well documented biochemically and you should be able to get that info. Malting, mashing and the like is another in-depth area covered by its own branch of brewing research. Much of the biotransformation via yeast stuff is still research in progress. Much of that still is anecdotal by non-scientific means. I am a biochemist and I share your interest in this information; but there is no one size fits all source.
    – brewchez
    Commented May 13, 2019 at 18:21
  • @brewchez Are there any books about low-level specifics about fermentation, malting, mashing, etc.? I have several books on more high-level stuff related to brewing and hops, but none go very deep unfortunately... for yeast transformations I could probably find some academic articles on the subject, but if the other stuff is pretty well-researched I would expect there to be books on it, but I haven't found any. Commented May 13, 2019 at 18:27
  • The association of brewing chemists is probably a great place to start for scholarly research based articles. asbcnet.org/Pages/default.aspx Then there is the master brewers association book list as a place to start too. my.mbaa.com/mbaastore I hope that helps. Happy reading... then you'll be the expert and you can write that one book you are looking for!
    – brewchez
    Commented May 14, 2019 at 12:23

1 Answer 1


Everything you're asking for in answers are covered in a variety of brewing books. But no single source covers everything your asking.

  1. Grain enzymes. This is basic and covered in all beginer brewing books. How to brew by Palmer has a great table on temps, enzymes and protein interactions. Short answer, alpha and beta amylase are the enzymes that convert the starch to fermentable sugars but are not "made" in a brewing process, they're already in the grain.

  2. Bacteria. Ethanol to Acid conversion is from acetobacteria and has no place in beers, even sour beers. It's used in making vinegar etc. Lactobacillus is what makes sour beers converting sugars to acid and is also naturally occuring in grains.

  3. Kombucha uses a SCOBY which is a pairing of fungus and bacteria. Also used in some Asian beers but mostly saki.

  4. Hibiscus Saison. I've worked with this flower a lot. It has a unique property, hydroxycitric acid. Which can be hard to balance. It works very well in IPAs with an IBU above 80 which masks the acid bite. Other styles are balanced with residual sugars usually a FG of 1.016-1.018 does well. Trick is to back off on the bittering hops and allow the acid to balance the beer. Its best as a late fermentation addition IMO but also good for a flame out at 165°F. Hydroxycitric acid is an enzyme inhibitor, so do not add it to the mash.

  5. Lemon/lime juice in cooking books don't really describe what's going on well. Many raw fish dishes will use acidic juice. In short it's a chemical pasteurization that most harmful bacteria / parasites can't survive by lowering the ph. Also helps break down protien fibers to make it tender.

Hope this helps.

  • Doesn't Acetobacteria have a place in certain styles, i.e. Flanders Red
    – Kingfisher
    Commented May 21, 2019 at 13:17
  • @Kingfisher true, Flanders red does use acetobacter, but it is haulted before it can go to pickle juice. But it is the exception and not all Flanders reds are made the historical way. Commented May 23, 2019 at 2:17

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