Fermenting stuff

Ken writes:

Somewhere along the line, for a birthday or Christmas or something, I acquired a copy of Sandor E. Katz’s “The Art of Fermentation”, which is a great book and well worth a look if you think you might be interested in learning about fermented foods and beverages from a practitioner’s perspective. It is written in a leisurely pace full of practical illustration and anecdote. The recipes are rather approximate and offer more guidelines and jumping off points than definite rules for anything. It’s a great book and it really works. I’ve already made some sauerkraut, which tastes like, well sauerkraut (a mixed success, in other words, but a good starting off point for kimchi and more fun stuff).

SauerkrautKen made this.

But, I do have one reservation about the book. Katz’s guidance about bottling is a bit laissez faire. He does warn would be bottlers to be cautious about sealing fermenting food and beverages in glass containers, but really this is an area that is so important that actual facts and principles are required. Katz tells you fill a plastic bottle with whatever you’re fermenting, which allows you to gauge the progress of carbonation by the squeeziness of the plastic bottle. Once it has become drum tight, you need to move the glass bottles to fridge to slow fermentation and you need to consume the refrigerated food or beverage soon afterwards. But really, it would be better to have control over how much carbonation will take place so that one can store the finished products in the cupboard in the secure knowledge that they will not explode. That’s definitely the feeling in the homebrewing community.

One reason why he doesn’t give more specific guidance is that different microbes presumably carbonate beverages at different rates. Yeast and lactic acid bacteria, for example, work on sugars differently, and for all I know, the action of lactic acid bacteria produces less CO2 per gram of fermentable extract than a yeast would. Since there’s no practical way of telling what microbe is fermenting your sauerkraut, you couldn’t calculate in advance (other than by experience) how much carbonation you will get from a certain base material.

On the other hand, it would certainly be useful to take the behaviour of yeast as a basis for bottling fermenting beverages, since yeast usually have a role in their production and since it is well understood. There are some very useful quasi-technical websites out there explaining things in detail for home brewers, for example, this awesome post by Braukaiser. Another useful guide is John Palmer’s How to Brew

How much of what sort of sugar you add to your bottles for carbonation depends on a) what sort of sugar you use, b) the temperature of your ferment (beer etc.) and c) how fizzy you want it to be. Yeast break down 1 gramme of sugar into roughly equal parts of ethanol and carbon dioxide (CO2). How much of an affect sugar has depends on its composition, since some highly fermentable sugars like honey and molasses actually also contain some water, and what type of sugar it is, since dry malt extract also contains sugars that yeast cannot metabolise. Ordinary cane sugar is for practical purposes 100% dry and 100% fermentable, so every gramme of it, per litre, will be converted into 0.5 grammes of carbon dioxide per litre, or since 1g/l is 1 volume of CO2 per volume, 0.25 litres of CO2 per litre.
You also need to know how much CO2 is already in your beer, which, if your fermenter is open to the atmosphere, is determined by its temperature. Cooler liquids contain more CO2 than warmer ones. You need to consult a table, such as this one, to know how much CO2 is present (incidentally, if you do consult that table, then if your fermenter is open to the atmosphere, i.e. your ferment is not under any pressure, the values you need are in the first column (zero gauge pressure)). You also need to know how much fizziness you want (the previously mentioned table contains a guide correlating beer styles with amounts of CO2). A reasonably effervescent beer might have two volumes of CO2 per volume of liquid, or 4g/l. According to that table, if your beer is at 18C, it will have 1.8g/l CO2 in it already, so you need to add 2.2g/l, i.e. 4.4g/l fermentable extract, which if you’re using 100% fermentable 100% dry sugar is 4.4g/l sugar. This calculation assumes your beer/whatever has no unfermented sugars in it at present, i.e. that fermentation has already come to a halt, which is not necessarily true. This brings me to the other thing I meant to say about Katz’s discussion of carbonation. He doesn’t sell the benefits of a hydrometer forcefully enough. In homebrew circles, you won’t find a serious brewer without a hydrometer. A hydrometer measures the density of the beer/whatever relative to the density of water. It can thus be used to accurately calculate the percentage of alcohol (ABV) of your beverage. More pertinently, it can tell you when your beverage has completely finished fermenting. If your hydrometer reading doesn’t change for three days, then it’s finished.


One thought on “Fermenting stuff

  1. Mairi Jay

    And, I’m seriously impressed by how much you know. It seems to me that brewing and fermenting calls on different sides of your nature – the scientist/mathematician and the artist. I love it.

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