(Non-Dairy Milk Only)

Line Fermentation requires a length of food-grade flexible plastic tube (gallery) anchored at both ends with one end higher than the other; the top end is open for re-filling and the lower end is sealed to a tap or spigot to control the flow of milk.

The word ‘line’ in the title is used to emphasise that – unlike the traditional method – fermentation does not happen at random but within the fairly narrow line defined by the tube. This difference has important consequences in practical terms. Re- filling is achieved by replacing the temporary stopper at the top end with a kitchen funnel;
The fresh batch of  milk then remains in the funnel until the spigot is opened and the fermented milk in the gallery is flushed out and is caught in a pot. This harvest is raw yogurt and – as with the traditional way – it must be strained to obtained yogurt curd. In Line fermentation harvesting follows and depends on re-filling.

Line Fermenter design for Pilot Test

Testing with this design ran for a full year between July 2018 and July 2019 with the results showing that this design not only works well, but offers a simplification of the Traditional way of making yogurt, with no heating or stirring required.

Background to Line Fermentation
How did Line Fermentation come to be adopted as the best design? The answer lies in two separate considerations.

Dissatisfaction with the freshness and quality of yogurt

Curiosity about the possibility of carrying out fermentation in a tube.

That the two might complement each other was neither considered or even seen in the same context for some time. When eventually the possibility seemed worth exploring, the first step was a search for a tube made of a suitable material for a pilot project; given the need for transparency (for visual inspections) the search quickly narrowed down to two – glass and plastic with transparent food-grade plastic tube chosen as the most suitable on the grounds of robustness, availability, flexibility and cost*.

How Does Line Fermentation Work?
After investigating various options, a design shown above was chosen and tested over a period of one year; the results were impressive from the start including:

– Greater simplification of the process overall
​
– No need for either heating or stirring, both of which have negative effects
​
– A significant increase in quality and taste of the yogurt produced.

Above all, no negative effects were noted. Also there was found to be no need for a starter to get fermentation going, the reason possibly resting on a small amount of the Probiotic culture that remains in the tube following harvesting; this ‘resident culture’ once established is stimulated to multiply and grow each time fresh milk is added.

A second benefit arises as a consequence of the way that the resident Probiotic culture modifies its environment by making it so acid that unwanted bacteria are unable to establish themselves; at one move this eliminates the need for shutdown and sterilisation of equipment, in effect turning fermentation from a batch to a continuous process.

The time required for human involvement was significantly reduced to five minutes or less for the whole fermentation process (excluding post-fermentation straining etc)

Finally, a comment on the improved taste; yogurt produced by Line Fermentation requires no added sugar – it is naturally sweet and this is possibly because there are very few dead or dying bacteria present (these do not taste good) as compared to Traditionally prepared yogurt; the reasons for this are technical, to do with the lack of disruption to the natural development of Probiotic culture, as a result of heating and stirring.

The results were very encouraging, so testing continued with several designs of Line
Fermenter which underlined the original test results.
​What’s Next for Line Fermentation?

As for the future, the options for Line Fermentation seem bright. With potential applications in other liquid fermentation processes in addition to making yogurt, it looks possible destined become a fast-growing area for development over coming years. However, many questions including the exact details of how the scheme works and potential limitations in scaling-up, remain unanswered, begging further investigation.