The detailed account which follows is in practice much simpler than it seems.



Filling Level and Gallery Capacity

The Dynamic Fermenter is now ready for a few vital finishing touches

i – Use a permanent marker to leave a clear and visible mark on the tube to show
where you will fill to with milk (‘Filling Level’). The actual location is not important
so long as the mark is below the lowest point of the wine bottle stopper.

ii – Check the spigot is closed, then:

  •           fill the gallery to the filling level mark with tap water
  •           open the spigot and run the water out  into a measuring cylinder
  •           read off the volume  and write down as the ‘gallery capacity’

Gallery capacity  should be re-checked every few weeks as any significant changes will reveal a potential leaks (unlikely) or possibly a build up of material inside the gallery or spigot.

This is probably also a good time to practice using the spigot for filling operations (so you close it exactly when you reach the filling level). It’s also useful to have a kitchen roll to hand when filling – spills are all but inevitable, especially at first.

Before starting on the next task (Priming the gallery wall) you will need a supply of live, organic soya yogurt and additive-free organic soya milk.

A word about organic soya milk and live organic soya yogurt:

‘Organic’ soya and yogurt contains no traces of pesticide (which could interfere with bacterial activity); go for varieties with no additives (Provamel is available in 500ml cartons and is preferable to the larger cartons as it is less likely to go ‘off” before you get round to using it – never be tempted to use milk that has started to go off as it could contaminate the resident culture).

A colony of live bacteria is essential for priming; seek out ‘Live organic’ soya yogurt –  any other kind will not do the job.  (‘made using’ live bacterial cultures’ on the list of ingredients or ‘bacterial  cultures’ does not count – the phrasing is misleading and does not mean the culture is ‘live’ – in fact it won’t be).

If you are feeling particularly adventurous you can provide your own starter culture from chilli pepper stems and soya milk – there are video clips on ‘Youtube’ click here that guide you through the process (and no, the yogurt doesn’t taste of chili).

Priming the Gallery

Numbers refer to the schematic ‘Priming the gallery/ establishing a routine’ beneath the text here.

  • Add 2 teaspoons of the live yogurt to  100ml milk
  • Stir slowly to ensure a good mix without introducing more air than necessary
  • Close the spigot
  • Replace the wine bottle stopper with the funnel *, which should be a good firm fit (1)
  • Add an amount of priming mix equal to the gallery capacity to the funnel (2)
  • If necessary, open the spigot to allow the mix to flood the gallery (3/4)
  • Finally, replace the funnel with the wine stopper (5) and allow the priming mix to do its job (several hours at least)

*A word about the funnel. This must be specifically a kitchen (food grade) funnel. If you feel round the stem of most funnels of this kind you will notice several spines running down the outside of the funnel at the top of the stem; these need paring back flush using a sharp blade, otherwise milk will leak from the funnel.

Filling/Harvesting  (5 to 8 on the schematic below):
As filling and harvesting  happen at the same time, we consider these two operations under the same heading. Once a batch milk is in the funnel and the spigot is opened, gravity ensures that the fresh milk pushes the fermented milk out of the gallery; the art is in closing the spigot at the right time to ensure the liquid level in the tube is at the same point as the filling level mark. A routine which has proved useful is then:

  • Dilute the soya milk to 60-75% of original strength; this should become standard practice  as this prevents  milk setting  solid  in the gallery.
  • Allow between one hour and 3 hours, depending on the season ‘retention time‘ milk to ferment in the gallery the first time; if more than a trace of milk appears in the whey after straining the curds (see below), give the milk a longer retention time in the gallery next time. When milk is turned into solid cream-coloured curd and whey (a colourless liquid).

The best timetable is probably the one that suits you and feeds the culture regularly; it may be useful if you record dates and times that you filled the gallery (plus anything else that seems noteworthy) in your log book, for the first few weeks at least.

(Remember that any attempt to transfer the harvest from the gallery is unlikely to happen while the wine bottle stopper remains in place!)

Straining the raw yogurt
Straining to separate curds from whey is not essential but widely practised; it is best however to stop before all the whey has been removed, otherwise the texture becomes rubbery (rule of thumb – strain until the residue fails to move when the strainer is shaken – when the total harvest from several batches is done together this takes a bit over an hour).Essential equipment for separating curds from whey includes:

A kitchen strainer/collander

A large bowl (or better,  a jug with a pouring spout) to hold the strainer plus:

      • a square of cheesecloth (eg 50cmx50cm) that can be folded to provide a double layer
      • a palette knife or similar with a long flat blade (to remove the curds from cheesecloth)
      • A small clean, dry, transparent tub + lid for storage of yogurt curd.
      • A bottle for storage of whey (or use in making soup)

Prepared in this way, the fresh curd will be creamy white with the recognisable texture and taste of natural yogurt but a fuller, rounded taste than the shop bought equivalent. If it has been kept in cold storage it is worth  removing the yogurt from the fridge half an hour or more before consumption as this will give time for it  to adjust to room temperature – cold yogurt anaesthetises taste buds!

Consume as fresh as possible (the taste immediately after separating curds from whey is incomparable, but does not last!) after adding chopped fruit, nuts, flavours etc  to curd  according to personal taste. Keep the whey (in the fridge) for making soups or cooking.

Checking progress
The best way to monitor progress at the point of harvesting yogurt from a Dynamic Fermenter is your sense of taste and smell; the test is simple and has proved effective over the course of many thousands of years as a way of  warning us against unsuitable food.

In brief, the advice is: if a batch smells unpleasant (in over 15 months of Dynamic Fermentation, this has never happened), get rid of it or add it to your compost bin  . If it smells a bit sour or lemony, it is fine to taste.

                                                                     ……….. If it smells OK and a small sample tastes OK  it is safe to consume!

Estimating retention time  
‘Retention time’ is a phrase meaning the length of time milk is left to ferment in the gallery. An estimate of minimum retention time is best made after a little experimenting (any more than a trace of milk in the whey means the retention time is too short); it may be useful to write this down; bear in mind it is likely to change a bit as the year moves from one season to the next.

Steps 5-8 in the schematic below show the routine for re-filling the gallery; from now on you will fill using (diluted) milk on its own. Note that there appears to be no advantage in allowing the milk to warm before adding to the gallery – adding straight from the fridge seems to cause no problems (providing your fridge is set to ‘cool’ – eg 7ºC – rather than cold .

When the ‘priming mix’ is flushed from the gallery by the first batch of (diluted) milk , some of the yogurt bacteria remain in the gallery (either attached to or close to the inner wall)  where they will form a new yogurt culture each time a new batch of milk is added. In this way the resident culture is perpetually renewed.

The schematic which follows is an attempt to show the sequence of events as described in this section at a glance; it may be useful to enlarge the image.

The Dynamic Fermentation Process

Catering for individuals and groups
While seeking to provide yogurt of the highest quality and maximum live bacteria content, Dynamic Fermentation produces yogurt in much smaller quantities. The Dynamic Fermenter shown in ‘Image 1’ for instance (see here) produced around 35g (1.1 oz or more than a level dessertspoon) of  yogurt curd from each 72ml batch of diluted milk, enough  for one person as a topping for breakfast or dessert.

Where families or larger groups are involved, running more than one batch per day or alternatively scaling up to build a larger fermenter are alternatives worth exploring (see ‘FAQs’). While beyond the scope of the pilot project, it should be possible using a combination of these options to produce enough yogurt to produce a reasonable amount of yogurt (35g per person) for groups of up to 25 adults without a problem.