---
title: Low-tech, low-energy yoghurt making
draft: true
date: 2024-05-25 21:00
---

I make yoghurt. I'm continuously tweaking and experimenting with the procedure,
to try to make it as efficient, easy, and low-energy as possible.

There's a tension between taste/texture, energy use, and ease of the process.
Yoghurt is the result of various species of bacteria fermenting milk.
The bacteria in question are classified as 'thermophilic' meaning they
thrive in fairly warm temperatures of 30-50 degrees Celcius.
Since they need typically 8-12 hours to do their thing,
that's a not-insignificant amount of energy use.
Further, I usually heat the milk well above that first, for two reasons.

First, for safety. Though I'm personally not too concerned about consuming
unpasteurized milk from healthy cows, I do like to reduce the risk
especially if things are going to be stored for a while.

The second reason I heat the milk has more to to with taste.
Heating the milk to 91 degrees breaks down proteins in the milk,
which allows the bacteria to get a lot more done,
resulting in a very firm yoghurt which I much prefer.

I probably like this so much because the yoghurt my mother used to make was so thick and firm.
But she made it with powdered milk,
which means you can 'supersaturate' the milk proteins.
Nowadays I avoid such heavily processed things as powdered milk.

I like to try to do things as 'low tech' as possible,
to be mindful of energy use but also just because it's a fun challenge
that grows my skills and keeps me learning.
So my method of incubating yoghurt is with a 'hay box'.
That's an insulated container which keeps food hot/warm for slow cooking
(we do all our water-cooked foods in here, like potatoes or rice).
In our case it's a plywood box stuffed with eight centimetres of wool
that doubles as a seat.
So, for the long wait, I'm using no extra energy at all.
The yoghurt goes in at 49 degrees, and comes out the next morning, 8-12 hours later,
at around 38 degrees -- still within the yoghurt-making range.

This phase is not only low-energy, it's extremely hands-off (I'm sleeping the whole time).
But it's getting everything too this point which is both energy- and attention intensive.
The effort required often would put me off doing it.
But I've persevered and can say that its starting to feel a lot easier,
thanks to practise and one piece of tech that I added to my process.

That is a simple digital thermometer with a probe on a long cable,
and, crucially, a temperature alarm. It cost about 19 Euros.
This allows me to set-and-forget the milk in the heating process.
Before, I would have to be constantly checking and stirring,
especially as I approached boiling point,
to avoid the milk boiling over.

There are also low-tech devices to alert for boiling over.
They're called pot minders or milk minders,
and they work by capturing and then releasing bubbles,
bouncing on the bottom of the pot and making a noise.
But I have not been able to find one for sale anywhere.
Moreover, the thermometer is useful for a multitude of things,
including makng the second phase, the cooldown, much easier too.

The goal is to heat the milk to 85 or 90, then keep it there for ten or twenty minutes,
then cool it to 49, add the yoghurt starter, and then get it in the incubator as quickly as possible.
In order to have enough mass to maintain heat overnight,
I heat about three litres of water to 49 degrees,
and put the two or three pots of yoghurt, 600ml each, in there.

The cooldown can go slow, but I usually speed it up by putting the pot of yoghurt in a tub of cold water.
The thermometer lets me cool it down as fast as possible and know when to stop.
It also helps me mix the water accurately. I pour boiling or near-boiling water
into cold water and stir, checking and repeating until I get the right temperature.

Today I did this process, and I feel like I've hit on a routine that works well and is reproducable,
takes as little time as possible, and saves some energy.

I re-use the cooling water as the basis for the incubating bath. Today this water was 27 degrees when it had
absorbed the energy from the heated milk. That saves quite a bit of energy since that's already a third of the difference from tap water (16 degrees) to my target of 49. I also had just enough of this warm water left over for washing up afterwards.

I've always been hesitant to do this, for heygiene reasons. But I figure if I work really clean, and since the yoghurt
is sealed in the pots, it should be ok. I think if I was selling yoghurt I'd need to be more strict about this.

