22 May 2014 I've found that whisking my
freshly-chilled batch leaves it rather grainy. For no
particular reason, I recently decided to pour off the
tablespoon or so of clear liquid from the top of the
Thermos before pouring the yogurt into its container.
Result: a much smoother and creamier product. Why? I
have no idea!
I suppose I could be classified as a ’yogurt addict’
because I eat around 200 grams for breakfast most days,
mixed with my
home-blended muesli. I’ve been doing this for quite
a few years, and for most of that time my yogurt-of-choice
was Danone Activia. Because our village shops - Co-op and
One-Stop - don’t sell Activia, the regular alternatives
have always been Onken and Yeo Valley, and the latter has
become my real favourite as it’s lusciously thick and
creamy, more tangy than the others and, surprisingly,
contains only 4.2% fat.
My loyalty to Yeo Valley became even stronger after
seeing their premises in the West Country and a recent
BBC-TV series on the food industry, which identified
Danone as one of the scarier food manufacturers.
I particularly like cold stewed prunes with my muesli,
and I buy French ’Jumbo’ prunes from Holland and Barrett -
by far the best I’ve found in this country!
Anyway, I have recently seen both Nigel Slater and Hugh
Fearnley-Whittingstall making their own yogurt on TV and,
being (as evidenced by this site) an obsessive food
experimenter, I decided to have a go (the cost-saving
would be fairly trivial, but I suppose every little
helps!). Yesterday (10 January 2011) was the day.
After a bit of googling (and as a faithful Observer
reader) I decided to trust Nigel.
In the absence of milk powder I went right back to basics
for the first trial.
Now, after about 16 weeks, I feel pretty confident, so -
for those without the patience of interest to follow my
experiments - here is my recipe...
Pour a litre of milk - preferably whole milk, but I’ve
used both whole and a half-and-half mix of whole and
semi-skimmed, depending on what’s been in the fridge, and
both have been fine - into a saucepan and start heating.
When this is getting warm, add 45 grams of powdered
skimmed milk (readily available from supermarkets) and
stir to mix thoroughly (I use a wire whisk).
Meanwhile, fill your vacuum flask (I use a
stainless-steel Thermos) right to the top with boiling
water and screw the top on. This both sterilises the flask
and preheats it so the mixture won’t lose temperature when
You need a fairly accurate thermometer for reliable
results - I have a
mid-range digital thermometer (about £20 from Nisbets)
but a cheaper one will do.
When the milk mix reaches 85°C, turn off the heat, empty
the flask, pour in the mix and screw in the stopper. This
temperature isn’t critical, as explained below, but the
next one needs to be pretty accurate. This will
ultra-pasteurise the mix and denature the milk proteins in
a beneficial way, giving you a thicker yogurt..
After 30 minutes (also not highly critical and also
explained below) pour the mix back into the saucepan.
Re-fill the flask with boiling water.
Leave the mix to to cool to 46°C - about half an hour
should do it, reheating if it cools too far. I don’t know
how critical this temperature is, but I suspect it’s the
optimum for the bacterial action we’re after. I think the
bacteria go on working as the mixture cools, but a
temperature much higher would kill your bugs, so if you’re
not sure of your thermometer err on the low side.
Add one teaspoon (more if you like) of your favourite
live plain yogurt and stir in. Once you have some
home-made yogurt, use this instead for further batches -
mine’s been going fine for months now.
Again, empty the flask and pour in the mix. Stopper it
and leave. I’ve left it for anything between eight hours
and 24, and it seems to get more tangy if you leave it
longer. However, the 24-hour batch (an accident - I forgot
to decant it!) wasn’t as good either in flavour or in
When you’ve waited long enough, open the flask and check
that the mix has set. If it has, you’ll probably need to
get a long-handled spoon or something similar to break the
set before you can pour your yogurt into a container and
put it in the fridge. When cold, beat it until smooth with
a balloon whisk.
The worst bit is cleaning all the coagulated protein off
the inside of the flask: I use a long-handled washing-up
Now the history...
Yogurt Mk I
It is essential to sterilise - or at the very least pasteurise
(see below) - the milk to ensure that the yogurt-making
bacteria have no unwanted and potentially dangerous
competition. I didn’t want to bring the milk right to
boiling point, because this forms a skin and changes the
flavour, so I settled for raising one litre of whole milk
to 90°C in a saucepan on the gas hob. I then turned off
the gas and left the pan with my
latest digital thermometer probe immersed in the
milk and the lid on until the temperature had dropped to
Meanwhile, I thoroughly washed a one-litre stainless
steel Thermos flask and filled it with boiling water, both
to sterilise it and to ensure that the temperature of the
milk wouldn’t drop when poured in.
When the thermometer read 46°C, I stirred in four level
tablespoons of Yeo Valley yogurt (natural, of course!) and
brought the temperature back up to 46°C on a very low gas,
stirring constantly with the thermometer probe. I then
poured the mixture into the Thermos, screwed down the top
and put the cup on too for extra insulation. (With this
flask, you can unscrew the whole plastic top rather than
just the stopper, which gives a wider mouth to pour into.)
That was at about 1pm. Early in the evening I tried a
quick teaspoonful: smooth, mild and quite thick. I decided
to give it some more time as I like a strong lactic
flavour - and then forgot to do anything at bedtime! At
8am, however, it was still very palatable, so I decanted
it into a basin, slapped on some clingfilm and put it in
Of course, when it was time for a late breakfast I
couldn’t resist trying it with my muesli, although it was
still slightly lukewarm. It was a bit lumpy, and I thought
at first that the whey had separated out, but this proved
not to be the case.
Pretty good, I thought, though still rather mild for my
taste. I’m looking forward to trying it fully chilled.
At this point I thought I’d better check out a bit of
the science, so I consulted Harold McGee’s superb On
Food and Cooking: the Science and Lore of the Kitchen.
I’ve referred to this magnificent book many times in The
Online Cookbook: it is, quite simply, the
definitive source of reference for the home cook
interested in the scientific side of cooking - and McGee
is, by the way, a close friend and collaborator of Heston
I had had a narrow miss with my choice of 90°C for the
preheating, which wasn’t bad considering that I was simply
wanting to sterilise the milk without cooking it.
Pasteurisation is done at much lower temperatures:
holding the temperature at 62°C for 30 minutes and at 71°C
for a mere 15 seconds will have the same effect, which
McGee says will ’destroy all disease-causing organisms
and most others as well’. As we know from
experience, though, pasteurised milk that hasn’t been
unsealed will go sour even in the fridge after a few days,
whereas sterilised (UHT) milk (the stuff the French use,
which tastes like watered-down Carnation) can be stored at
room temperature for months.
It turns out that holding the milk for yogurt at ’about
85°C’ and ’holding it there for about half an
hour’ both pasteurises the milk very thoroughly and
’denatures the whey proteins to some extent, unfolding
the initially compact molecules into longer structures
that increase the viscosity - thicken the texture - of
the liquid. And in the case of yogurt, it results in a
firmer gel that is less prone to separating into curds
and whey.’ If you want to know why this
happens, you’ll have to buy the book - and if you’ve read
this far you probably should!
The other point for attention is the common use of
powdered milk in yogurt. Apparently this provides more
milk protein without adding water or much fat, helping to
make a thicker, smoother yogurt. Nigel Slater uses two
tablespoons per half-litre.
So the next batch will he heat-treated according to
McGee’s information above and will include powdered
At 1pm, 24 hours after putting the yogurt in the flask,
I tasted the fully-chilled product. The texture is a bit
lumpy, and if anything it’s a bit tangier than the Yeo
Valley yogurt I used to innoculate it, so maybe 20 hours
is a bit too long. Thick and creamy, though, with
absolutely no sign of the whey separating out. Not bad for
a first attempt!
13 January 2011
I’ve just eaten the last full helping of my first batch
of yogurt - there’s enough left in the bowl to provide
four tablespoons to innoculate the next litre, with maybe
a bit to be used in a dessert. At one stage, I thought I
could see some whey separating out, but I think it more
probably condensation that had formed on the clingfilm
covering the bowl: the texture of the yogurt itself hasn’t
Yesterday I got some ’instant dried skimmed milk’ from
our village Co-op. I think the ’instant’ refers to the
fact that it can be mixed with cold water. It was on the
same shelf as Marvel, and is probably the same thing
without the brand and marketing.
So today I will be making my second batch with the
addition of the dried milk. The function of the dried milk
is to add extra protein and lactose (milk sugar). The
first is what coagulates to thicken the yogurt, under the
influence of the lactic acid produced as the bacteria
digest the sugar. The additional protein should produce a
thicker yogurt, and possibly in the process a more acid
Obviously, as the dried milk in there to increase the
protein content of the mix, it should be mixed in before
Yogurt Mk II
The litre of whole milk I bought this morning cost 87p,
compared with £2.30 for two 500ml cartons of Onken yogurt
- over 2½ times as much for the same money.
I weighed four tablespoons of dried skimmed milk at 38
grams (I’ll weigh rather than measure in future and, if
the result is satisfactory, use 40 grams in future), intending
to add it to the cold milk in the saucepan. Unfortunately
I was so preoccupied with the problem of heating the mix
to 85°C and keeping it there that I only spotted the dried
milk still in the scale-pan about ten minutes into the
heat-treatment! Not to worry: in it went for the remaining
To make reconstituted skimmed milk, this quantity of
dried milk would be mixed with 380ml of water , so it
should add around 40% to the protein and lactose in the
For most of this time I managed to keep the milk within
a degree of the required temperature by adjusting the
gas-ring by minute amounts - and McGee does say ’about
85°C’. However, this meant staying with the process
for the whole hour, stirring almost constantly with the
thermometer probe - not something I’ll want to do every
week. So the next experiment will be to use the water-bath
I bought for my sous vide’ experiments - perhaps
putting half a litre of mix in each of two jugs immersed
in the temperature-controlled water.
Meanwhile, the Thermos had been rinsed and filled to the
brim with boiling water, which was left to cool until the
hour was up. At 12:15pm, when the temperature had dropped
to 46°C, in went four tablespoons of the previous batch of
yogurt. I plan to sample the result before going to bed
before deciding whether or not to leave it overnight.
40 grams of the Co-op dried milk contains 14.25 grams of
protein, 20 grams of carbohydrate (all sugar) and only a
quarter of a gram of fat, giving a total of 140
kilocalories. What happens to this in yogurt-making I’m
not sure. The protein should stay about the same and the
sugar should be consumed to produce lactic acid, I guess.
Disorganised again! I forgot to check this batch before
bed, but did so at 2:45am when I had to come down for some
cough medicine! It was already thicker than Mk I, so I extracted
the yogurt from the flask into a 2-pint pudding basin as
before. (I emphasise ’extracted’ because I had to insert a
long-handled spoon and disturb the yogurt before it would
come out, and even then quite a lot was left at the bottom
of the flask, which a good shake dislodged. The basin was
clingfilmed and put in the fridge to await breakfast time.
The texture was similar to that of the previous batch -
somewhat lumpy - and the flavour perhaps a little
stronger. Very acceptable, though. This morning (16
January) I decided to risk whisking it before breakfast.
It took quite a bit of work to get it smooth, but the
result was very creamy.
Don’t change two variables in one go!
I should have remembered this fundamental rule of
experimentation and tried first the heat-treatment alone
and then the addition of powdered milk alone before
combining the two. However, since the result was excellent
I probably won’t bother backtracking, and may never know
which of the two changes made the most difference!
Yogurt still smooth and free from separated whey this
morning. Also, my old mate Pete ’Voltarol’ tells me he
used to make yogurt, also in a Thermos, and sometimes
strained it to get thicker Greek-style yogurt. I checked
this out, and it seems to be about draining off the whey
rather that actually straining the yogurt. I don’t know if
it works if the yogurt has no ’free’ whey.
Yogurt Mk III
24 January 2011 This batch was made two
days ago. After the tedium of keeping the temperature of
the milk at ’about 85°C’ for an hour, I had what
seemed like a brainwave: heat the milk to a bit over that
temperature and tip into a pre-heated Thermos. I couldn’t
really see or taste any significant difference when I
decanted the yogurt yesterday (if anything this was a bit
more difficult than with the previous batch, so a
bit thicker), and after whisking to a smooth texture I had
some with my muesli this morning. The texture and flavour
were just as good as before, so I will stick to this
process unless I’m distracted by any more sudden
Yogurt Mk IV
31 January 2011 (Monday) I
made a new batch, as above, at Saturday lunchtime. The
only difference was that, when I decanted it from the
Thermos, I did so into a larger basin so that I could
whisk it more vigorously before tipping it into a smaller
one - this saved a lot of splatter. I had some on my
muesli this morning and it was just as good as before.
Yogurts Mk V, VI, VII and VIII
25 February 2011 (Friday) Four
more batches done, including one whipped with the handheld
electric mixer, and I’m still very happy with the taste
and viscosity of the result. It’s not as smooth as the
commercial product - a little granular - but if anything
the taste is cleaner, eliciting a satisfied ’Aaaaaah!’ as
the last scrapings from the muesli dish go down. One batch
was accidentally left in the Thermos for nearly 24 hours,
but seemed none the worse for this.
The reason this week’s report is on a Friday is that I
used some of the yogurt in a 50:50 mix with Patak’s Madras
curry sauce. I wondered if this mixture might split, but
it was fine, cooling this fierce curry enough to make it
acceptable to Patricia, who has a low pain threshold when
it comes to chilli.
So that’s eight litres of very acceptable yogurt for,
counting the milk and the skimmed-milk powder, under £8.
The same quantity of Yeo the Valley product would have
cost £18.40. As far as I can see, I’ll be able to go on
innoculating each batch from the previous one
indefinitely. So it will be worth investing in...
A more suitable Thermos
I’ve been using a tall, slim stainless steel Thermos,
which is fiendishly difficult to clean because the yogurt
deposit left behind sticks very firmly to the metal. I had
a look at the Thermos Online site and found a wide-mouthed one among the food
flasks. Amazingly this turned up overnight. It’s not as
deep as the skinny one, has a wider mouth and
200ml more capacity. I’ll be able to can scrub it out,
rather than relying on squirting water in and shaking it
around, then resorting to bleach, and there will be a bit
of headroom so I don’t spill as much of my mixture.
I chose to buy this from Thermos direct desite it being
a couple of quid on Amazon, because I needed new tops and stoppers for our two skinny
flasks. When I read the instructions for the new
flask, I found out why the seals on these had failed: I’d
put them on a hot programme in the dishwasher and Thermos
only recommend warm water and washing-up liquid followed
by a hot rinse. Be warned.
Yogurt Mk IX
3 March 2011 Again, ignoring my own
warning not to change two variables at once, I made this
week’s batch in the new flask using only three rather than
four tablespoons of the previous batch as a starter. After
only eight hours the yogurt was fully set and at least as
good as any previous ones. The new flask proved much
easier to clean, first because I could get a brush to the
bottom but also because it has an easy-clean surface
I intend to reduce the quantity of starter progressively
because it seems sensible to use as much ’old’ yogurt as
possible, so the next batch will be made with two
Yogurt Mk X
8 March 2011 I really should read my own
notes! I came back to this page to double-check that the
heat treatment temperature is85°C (had a senior
moment and doubted my own memory) and realised that the
time required according to The Blessed Harold is about half
an hour - not the hour I’ve been using so far. So the
tenth batch has just gone in the Thermos for 30 minutes
(with only two tablespoons of starter this time).
I’m doing this batch just five days after the last one
because I’ve been eating a banana with yogurt and
Billingtons’ molasses sugar - even darker and more
strongly flavoured than dark musovado - for pudding at
dinner time. Delicious!
It was only when I was pouring the milk out of the
Thermos after the heat-treatment phase that I remembered I
hadn’t put in any milk powder - obviously this was a day
for senior moments. I stirred the powder in and completed
the process with no more errors. Although the milk powder
hadn’t had the benefit of the heat treatment, I couldn’t
detect any difference from the previous batches.
This batch was made with two tablespoons of starter, and
didn’t take any longer to thicken. The next will be done
with just one spoonful...
My yogurt isn’t quite as tangy as the Yeo Valley product
that provided the original starter. Very nice, but just a
bit bland. The lactic acid comes from the bacteria
fermenting the lactose (milk sugar) in the milk and acts
as a preservative because not many bacteria like an acid
environment (hence pickling in vinegar). So I started
wondering if I could improve the tang by adding some
lactose. To my surprise, there seems to be plenty on offer
in small quantities in the USA, but none in anything but
huge sacks in the UK. It seems that the only way to
increase the lactose content, and therefore the acidity of
the finished product, would be to increase the amount of
powdered milk. I might up this from 40 to 50 grams in the
But that will be changing two variables at once again!
But hey - there’s only a litre of milk at risk!
Yogurt Mk XI
14 March 2011 This time I remembered to
mix the powdered skimmed milk (50 grams this time) to the
litre of fresh whole milk before heat-treating
the mix. At 85°C the mix was poured into the Thermos,
which had been filled with boiling water to sterilise and
pre-heat it. After half an hour this time (!)
the mix was poured back into the saucepan to facilitate
cooling. Once it had cooled to 46°C, a fairly precisely
measured tablespoon of the previous batch was added and
the mix was poured from the pan into the Thermos and
sealed. Six hours later it had set fairly firmly.
This batch was definitely thicker than before, but if
anything a bit too thick - almost chalky in texture. If
I’m honet, I don’t think the taste was any more acid than
Yogurt Mk XII
22 March 2011 This time I split the
difference, adding 45 grams of powdered milk, and
innoculated the milk with just one level teaspoon of the
previous batch. To my delight, it set just as well as the
previous lot, so I’m now down to one twelfth of the
original four tablespoons!
Yogurt Mk XIII
28 March 2011 I was short of whole milk
when the need for this new batch arose, so I used 50/50
whole and semi-skimmed, again with 45 grams of powdered
milk and one level teaspoon of the previous batch. There
was not much difference - maybe the all-whole-milk is a
little smoother. At some point, I might try Nigel Slater’s
suggestion of adding a little cream for a luxury
And on it goes...
26 April 2011 Today’s will be about my
18th or 19th batch - I’ve stopped keeping count because
the yogurt seems totally reliable. The last batch got left
in the Thermos for almost 24 hours - by accident rather
than design, because I made it in the morning and forgot
to decant it before going to bed. It was fine, and very
noticeably more tangy, so there is obviously some lacose
left in the mix after 12 hours. I think I might try this
23 May 2011 Just an update... I can’t be
bothered to count back to see what generation my friendly
little bacteria are now, but it must be at least the 20th
and the yogurt is still excellent - if anything, getting
better. As with the sourdough,
there seems to be a good case for keeping one culture
going rather than starting a fresh one.
Interruption for a holiday
We left for a two-week visit to Normandy on the 22
August, and before going I stashed the last dregs of the
current batch of yogurt in the fridge to see if it would
survive to start the next. When we got back on the 5
September I was disappointed to find two orange and one
black spot on the surface. Given that the mold that forms
the rind on some of the more fragrant French cheeses
(including Livarot) is bright orange, I decided not to
risk using the stash as a starter. So this morning’s
breakast included freshly-purchased Yeo Valley yogurt, the
left-overs of which will be used to kick off a new
generation of yogurt. I found this a bit mild compared
with my home-made product.
The good news is that starters from the first batch (10
January) had made excellent - maybe even improving
- yogurt for over seven months.
9 September I made a new batch using one
tablespoon of Yeo Valley yogurt two days ago and had it
for breakfast today. A bit milder than my previous batch,
but I’m sure we’ll be back to normal after a few
5 October The most recent batch, using
one teaspoon of the previous one, was only left in the
flask for about eight hours. The result is milder and not
as thick, but still very palatable.
17 October The next batch was left from
mid-morning until bedtime and by then had set really well.
Until now I’ve been giving each batch a good beat by hand
with a wire balloon whisk, after which it thickens nicely
overnight in the fridge. This time I decided to try our
stick-blender. Bad move - it smoothed the yogurt nicely
but it didn’t thicken again, so I’d obviously broken down
the protein structure too much. Otherwise, as nice as
15 November The latest batch was left in
the flask for a little over 12 hours and was very firmly
set. Once into its fridge container, it was left for two
days before beating with the wire balloon whisk. The
result was very thick and pretty smooth. So it obviously
pays not to beat the yogurt until it’s really cold.
A new recruit Last week I visited my
accountant to get last year’s business accounts and tax
return sorted. As a bit of light relief we chatted about
home-made bread (she’s a bread-machine user) and yogurt.
Today I got the draft accounts attached to an email which
contained the following: P.S. Just to let you know on
Sunday I had a successful attempt at yogurt making,
using the thermos flask and thermometer method! I used
UHT semi-skimmed milk, and a bought yogurt as starter.
Yogurt was fairly thick, smooth, mild, and delicious. I
started another batch this morning experimenting using
the Sunday yogurt as a starter, so fingers crossed.
29 November I forgot to decant the last
batch until it had been in the flask for about 23 hours.
Perhaps it ended up a little tangier than the previous
12-hour batch, but tastes just as good and is very
2 July 2012 The lack of updates since
the end of November indicates that there have been no
problems keeping the culture started on the 9 September.
Recently I?ve been using semi-skimmed milk instead of
whole - simply because we buy gallons of this every week
and only buy whole milk when needed for sauces and
desserts - and the results have been just as satisfactory
as the ?full fat? ones. Today, I?ve started a batch with
mostly whole milk because that was left over from the
cheese sauce for a moussaka, topped up with a small amount
8 May 2013 The most recent batches have
been made entirely with semi-skimmed milk. I fill the big
Thermos to the bottom of the neck (1200ml), tip it into
the pan, rinse the flask and fill it with boiling water.
As the milk is heating I whisk in 50 grams of powdered
skimmed milk. When the thermometer hits 85°C I turn off
the gas, empty the flask and pour in the hot milk. After
30 minutes I decant it back into the pan to cool and
refill the flask with boiling water. It takes about
another 30 minutes to cool to 47°C, at which point I stir
in about a dessertspoonful of the last batch of yogurt and
tip the result back into the flask. The big innovation is
that I now ferment the yogurt for a full 24 hours,
which makes it a lot thicker and not excessively sour. A
rest in the fridge and a vigorous whisking have it ready