I managed to find the info again. It's from a podcast episode from way back in 2007, back during the first wave of podcasting.

So this comes directly from the guy who invented a very popular brewing sanitiser. He's a chemist by trade so he knows what he's talking about.

What you need is:

• Fresh bleach* (ideally unscented [although at the concentration you're working with it's not really that big of a deal], definitely nothing with any other additives - the cheap store-brand bleach is best. This will be 5% concentration but you can double-check if you want.)

• White vinegar (hold the gasps! This also needs to be 5%, don't use homemade vinegar or higher concentrations just use the normal stuff you find on the shelf at a grocery store.)

• An attention to detail, a distraction-free environment, and enough focus that you aren't going to make any silly mistakes.

(*Fresh bleach is stuff that is clear and that has a slight yellowy-green tint, that has a chlorine odour. If it's cloudy or it lacks the chlorine odour, it's degrading and it's unsuitable for sanitising.)

Here's the recipe:

1. Take 1.9L of water and add 3ml of bleach to the water.

2. Stir vigorously to disperse the bleach. You can rinse the measuring container into the water or you can get a separate measuring vessel for the next step.

3. Add 3ml of vinegar to the water and stir well.

You must do it in this order.

Never ever mix bleach and vinegar directly, or you will make toxic gas

(Just don't ever mix bleach with anything else, except in the above example following those steps.)

This is a no-rinse sanitiser, and in fact if you rinse this sanitiser off you will introduce bacteria into your vessel which will make the sanitiser less effective.

30s of contact will sanitise whatever surface it's on provided that the surface is clean before you use the sanitiser.

You can listen to the recipe here, although he uses imperial measurements and larger quantities because it's intended for homebrewers.

You could reduce the quantities in the recipe above but it gets fiddly. Using small syringes will make it easier to get to, say, the 1ml mark for the other ingredients if you're going to make up sanitiser in 630ml of water.

There's a degree of flexibility built into this recipe - you don't need to be so precise that it hurts. Don't take advantage of the margin of error and get lax about it but at the same time don't get the impression that this requires lab calibrated equipment. Working with slightly larger quantities is better in this respect because if you're aiming for, say, 0.25ml of bleach then it gets very easy to blow past the margin of error. And at the amount of ingredients we're talking, it's better to use a few cents of extra ingredients that will go to waste than it is to start playing around with quantities so small that you introduce a degree of risk which is completely avoidable. You can always use the leftover solution to sanitise other things for a bit of spring cleaning if it makes you feel better about not wasting resources.