Below is an article written by Sandor Katz. I meant to post it long ago as an accompaniment to my sauerkraut recipe post. It details the finer points of sauerkraut-making, like what kind of vessel to use, how much salt to use and how long to ferment. Here it is from his new book, The Revolution Will Not Be Microwaved...
Vegetable Fermentation Further Simplified
by Sandor Katz
(Excerpted from The Revolution Will Not Be Microwaved.)
A head of cabbage forgotten on an obscure shelf of your pantry will not spontaneously transform itself into sauerkraut. Vegetables left exposed to air start to grow molds, and if left long enough, those molds can reduce a head of cabbage to a puddle of slime, bearing no resemblance whatsoever to crunchy, delicious, and aromatic sauerkraut.
The simple key to successful vegetable fermentation is to make sure your vegetables are submerged in liquid. That’s it, the big secret. Usually the liquid is salty water, also known as brine, but fermentation can be done without salt, or with other liquids, such as wine or whey.
Typically, when fresh vegetables are chopped or grated in preparation
for fermentation—which creates greater surface area—salting pulls out
the vegetable juices via osmosis, and pounding or tamping the
vegetables breaks down cell walls to further release juices, so no
additional water is required. However, if the vegetables have lost
moisture during long storage, occasionally some water is needed; if
brine hasn’t risen to submerge the weighted vegetables by the following
day, add a little water. In the case of vegetables left whole (cabbage
heads, cucumbers, green tomatoes, string beans, okra, zucchini,
eggplant, peppers—try anything), the vegetables should be submerged in
The huge variety of vegetable ferments you can create all exist along
the spectrum from shredded and salted to whole and submerged in a
brine. Sometimes you use elements of each style, as in kimchi recipes
that call for soaking vegetables in a brine to soften them and leach
out bitter flavors, then pouring off excess brine and mixing in spices.
In some cases the liquid is what we’re after, flavored by the
vegetables and fermentation.
Pretty much any vegetable can be fermented. Use what is abundantly
available and be bold in your experimentation. Seaweeds are a wonderful
addition to ferments, as are fruits, though mostly fruit ferments go
through their process very quickly. I’ve even made delicious sauerkraut
with mashed potatoes layered in with the salted cabbage, as well as
kimchi with sticky rice layers. The sharp fermented starches are
delicious. The spicing of vegetable ferments is quite varied, too.
Kimchi typically includes red chili peppers, garlic, ginger, and
scallions. Sauerkraut might include caraway seeds (my favorite),
juniper berries, apples, or cranberries. New York–style sour pickles
are spiced with dill, garlic, and sometimes hot peppers. To keep
cucumbers crunchy, add to the brine some grape leaves or leaves of
horseradish, oak, currant, or cherry.
How much salt do you use? Traditionally vegetables have been
fermented with lots of salt. In addition to pulling water from the
vegetables, salt hardens pectins in the vegetables, rendering them
crunchier, and discourages the growth of bacteria other than
lactobacilli. By inhibiting competing bacteria, salt enables the
vegetables to ferment and to be stored for longer periods of time.
Since preservation has historically been one of the important
motivations for fermentation, ferments have tended to be quite salty.
But for health-conscious people interested primarily in flavor and
nutrition, less salt can be better. Salt lightly, to taste. It is
easier to add salt than to take it away, but if you oversalt, you can
dilute by adding water and/or more vegetables.
There is no magic
proportion of salt the process requires—it’s just personal preference.
As a starting point, try 3 tablespoons of salt per 5 pound of
vegetables. More salt will slow the fermentation process; less (or
none) will speed it up. Ferments with less salt may be more prone to
surface molds. You can leave out the salt or use various mineral-rich
substitutes such as celery juice (my favorite salt-free variation) or
seaweed. Just be sure the vegetables are submerged in the liquid.
Some people promote the idea that salt-free sauerkrauts contain
more beneficial organisms than salted krauts. I don’t believe that. The
most specific beneficial bacteria we’re after, Lactobacillus, is
salt-tolerant and abundantly present even in salty krauts; arguably,
salt-free ferments are more biodiverse, but this diversity often
results in mushy textures. Though it is possible to ferment vegetables
without salt, a little salt results in far superior flavor and
texture—and just as much beneficial bacteria. So again, salt to taste.
What kind of vessel should you use to hold your ferment? Avoid
metal, as salt and the acids created by fermentation will corrode it.
Heavy ceramic cylindrical crocks are the ideal fermentation vessels,
though they can be hard to find and expensive. Glass containers work
well, especially those with a cylindrical shape or with a wide mouth,
and so do nesting bowls. Crock pots with ceramic interiors make
effective fermentation vessels and can often be found in thrift stores.
In a pinch, you can use plastic, but even food-grade plastics leach
The reason a cylindrical shape is desirable is for ease of
weighting down the fermenting vegetables to keep them submerged rather
than floating to the top. I generally use a plate that just fits inside
the vessel, weighted down by a full jug of water, and I drape a cloth
over the top of the vessel to protect against flies. I call this the
“open-crock” method. Containers in other shapes can work with
improvisation, or you can manually press the vegetables to submerge
them in the liquid.
If the vegetables float to the top and remain exposed to air, they
are likely to develop mold. Sometimes, especially in hot weather, your
ferment may develop a film of white mold on its surface. This is very
common and will not hurt you or the kraut. Scrape off the mold as best
you can, don’t worry about particles that mix into the vegetables, and
enjoy the delicious ferment beneath. Specially designed Harsch crocks
eliminate this problem by creating an oxygen-free airspace around the
ferment. These German crocks are elegant but expensive. Another way to
avoid mold is by weighting the ferment in the vessel with water
contained in a double layer of plastic bags. The water will spread to
cover the entire surface, protecting it from aerobic surface molds. The
downside of this method, of course, is that your food comes into
prolonged contact with plastic, which leaches chemicals into the food.
I prefer to use the open-crock method and remove mold as necessary.
Whatever type of vessel you use, pack the vegetables into it with
some force (unless they are whole), in order to break down cell walls
and release juices. I use a blunt wooden tamping tool. You can
improvise with a piece of wood or your fist, or you can manually
massage and squeeze the vegetables, as described in the recipe for
massaged kale (see page 185). Once the vegetables are weighted down,
the salt will continue to pull moisture from the vegetables for many
hours yet. If, by the following day, the vegetables are not submerged,
add a little water.
How long do you ferment the vegetables? I wish I had an easy answer
to this question. “Ferment until ripe,” many recipes advise, but
ultimately you will have to decide when it is ripe. Sour flavor—from
lactic acid—develops over time. Longer fermentation translates to
tangier flavor. This happens more quickly in warm temperatures than in
cool ones. If you start your ferment at harvest time, in the autumn, as
temperatures are dropping, it can ferment for six months or longer.
This is how people survived before refrigeration and globalized food.
Many people, however, prefer the flavor of a mild ferment to that of a
strongly acidic one. When you are first experimenting, taste your
ferments early and often. Serve some after three days, then three days
later, and again three days after that. Familiarize yourself with the
spectrum of flavors that fermentation can create and see what you like.