Bacteria are your friends

10 02 2007

Partly because I like to show how clever I am, and partly because it annoys me that people pay so much for something so easy to make, here are my easy-peasy yogurt making instructions.

Actually, there’s many ways to make yogurt. Cos I’m all about the science, I’m going to quickly explain how yogurt happens – this way you’ll be able to extrapolate your own recipes in a jiffy because you’ll know what’s happening down there on microbe level. If you just want the recipe, skip to the end.

In a nutshell, the bacteria in yogurt eat a sugar that’s in milk. The way they eat the sugar leaves acid as a leftover. Because bacteria ain’t never heard of the idea of moderation, they hit the milk, think “PARTY!”, and charge around eating the sugar and reproducing like it’s going out of style. The milk becomes more and more acidified. Meanwhile, the milk protein, which is basically your NIMBY in the whole yogurt making process, starts having some issues with these low rent fuckos taking over the neighbourhood. Because proteins are such whinging bitches, once the acid level starts to rise, they stop floating around making milk all creamy, and pretty much lose it and get all tangled. The tangling of all the milk proteins is what makes yogurt solid. It’s a similar process to when your mp3 player headphones go from being neatly coiled up to escaping and looping around every bloody other thing in your bag.

There’s one other thing that’s important to know. Yogurt bacteria are living things. They can survive being chilled – basically they just hang out, get on with writing their blog or whatever and wait for some warmth to show up so they can orgy it up again. But they can’t handle being cooked. And cooked, for bacteria, is much the same as it is for humans – much above about 44°C things start looking grim.

The bacterial bacchanal comes to an end basically because they run out of food. I never said bacteria were smart, did I? Anyway, that’s when your yogurt is done, and you bung it in the fridge. A lot of the bacteria die off towards the end of the process as the food runs out, but there’s enough there (and by enough, we’re talking millions of the lil suckers) just hanging out that when you chuck a spoonful of it in your next batch of milk, the whole process can repeat itself.

Making yogurt – the thermos recipe
This is by far the easiest and cheapest way I’ve found to make yogurt.

You need:

– 1 (ish) cup of either skim milk powder or full cream milk powder
Because the bacteria metabolise the lactose (sugar) in milk, it doesn’t matter how much fat is in it. The end product will be slightly more or less creamy is all.

– 1L (ish) of cold water
Cold from the fridge, not from the tap. This is important.

– 1 yogurt thermos.
You can buy one for about $20 that rhymes with “cheesy, ho”, but with this recipe you can laugh smugly at all the people paying large sums of money for their pre-mixed packets that are basically just freeze-dried bacteria and some milk powder. Or you can fashion your own, MacGyver style, from a polystyrene box with a lid and two bowls/containers (one smaller than the other, and the smaller one should have a lid of some sort and sit inside the larger one). Or an esky. BE CREATIVE, KIDS.

– 1 kettle of boiling water.

– 1/2 cup or so of starter culture.
If you’re starting from scratch, nick off to the shop and grab yourself the cheapest little tub of yogurt you can find. Make sure it’s natural (flavoured ones make everything a little… strange) and has some kind of marketing-tastic claim about “live cultures” on it. Pasteurised yogurt won’t work as it has no live bacteria in it anymore. No live bacteria, no bacterial orgy, no yogurt. The numbers of bacteria slowly die off in ‘live’ yogurt as well, so if the starter culture is really old, it might not have enough left to do the job.

1. In your “Breezy, Beau” container or smaller plastic bowl, mix up your milk powder with some cold water to get a smooth liquid (you wanna make it with actual milk? Just wait, we’ll get to that). Take the time to get all the lumps out.

2. In another little bowl, or whatever, mix your starter culture with some more cold water to get a smooth paste.

3. Mix the two together in whatever container you are going to make the yogurt in, and use the rest of the cold water to top up the mixture. You want to aim for 1L of liquid in total. Stir til smooth. Or whisk madly and curse your impatience for not getting the lumps out earlier. Either way.

4. Pour the boiling water into the outside chamber of your “Freezy, Faux” or larger bowl. Put the lid on the whole contraption.

5. Come back in 7-9 hours. Congratulations, you’ve made yogurt! Pop it in the fridge to set a bit more.

Given we understand the microscopic working of this process, an important thing to notice with this method is the whole “cold water, boiling water” thing. Basically the thermos method starts with two different heats, and they equalise to the right temperature, and the thermos keeps it there for long enough for the yogurt fermentation to happen.

If your yogurt comes out really runny, it’s probably because the bacteria died before the right temperature was reached, that is, it got too hot for the poor darls. In which case, next time try either less boiling water, or a better starter culture. In summer, you’ll need less boiling water. In winter, a bit more.

Questions? Comments?

Q: I wanna make it with milk.
Alright, you can do that. I first learnt to make yogurt by the incubation method, which is basically:
1) boil milk to sterilise
2) wait for milk to cool down to 37-43°C
3) mix in starter culture
4) incubate mixture at 39°C for 7-9 hours.

Some people can do this with the pilot light in their oven, or on a windowsill, or whatever. Good luck to ’em. I say, boil your milk, cool it til cold, add in starter and proceed as per thermos method above. A lot less hassle and a lot harder to overcook.

A reason I like to use milk powder is you get to skip the whole sterilisation thing, although the flavour is slightly better with milk.

A word to the wise. Don’t skip the boiling milk to sterilise phase when using normal (non-powdered) milk.

Q: This yogurt tastes all tangy. I prefer a more artificial flavour.
You can add fruit and sugar or honey after it’s been in the fridge for a bit. I find that packets of fake sugar borrowed from cafes provide that authentic “sweetness”.

Q: You seem to have a tendency towards anthropomorphism. Bacteria is not a sentient being.
What of it? I also talk to inanimate objects on a semi-regular basis. I am told this is part of my charm/neurosis.

Get into it. Tell me how it goes.

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4 responses

11 02 2007
MikeFitz

Hi Sherd, Thanks for this explanation of the yoghurt-making process. This morning I tipped the milk bottle towards my morning coffee and was rudely woken up by large white chunks splashing into the mug. Crikey! The expiry date was only yesterday! Already my milk had spontaneously mutated to yoghurt.I wasn’t upset at all because I had read your blog post last night. “It’s just large molecules tangling around one another!”, I said to myself.

12 02 2007
mskp

the android has a product that rhymes with skeezy-eau, so we’ll probably not use this recipe. but i’m intrigued by the social life of germs, as deftly described by you, sherdie.actually, toby informed me recently that, as a condition of our marriage, i now own half the yoghurt maker. how i cheered.

12 02 2007
TOBYtoby

I was about to say I was the proud owner of a “Queasy? No!”. I have been buying the pre-mixes, because when you buy them in bulk they are actually quite cheap. BUT NOW … I can save the last bit of each batch to make the next.I got half a dog, kp got half a yoghurt maker.

12 02 2007
Sherd

Hmm, it’s hard to say who got the better end of the deal there. I mean, it’s like the “give someone a fish” proverb – half a dog will feed you for a meal, but half a yogurt maker and you’ll have fermented milk products forever!…boom tish…?*crickets*ok, obviously the world isn’t ready for my pet-eating humour.

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