Why Discard Starter: A Mathematical View.

You see this question pop up all the time in sourdough discussions:

“Why do I have to discard? I hate the idea of throwing anything away. Can’t I just keep feeding the starter?”

Although reducing the waste we produce as a species is a good thing, there are times when it’s actually more logical to NOT do so. And feeding a starter is one of those times.

Let’s first see about the starter when you’re just starting it up from scratch.

Early in your starter’s young life, within the first two weeks or so of starting a starter from scratch, there is absolutely no good reason to save the excess “flour soup” you’re cutting back. It has done it’s job and is spent, and really, it’s about 2 tablespoons of flour each day, this is not worth worrying about. Even if ditched directly into the trash or compost, it’s still not “wasted” any more than that nice dinner you ate yesterday was “wasted”: it was used to feed your starter, so it had a purpose and served it well.

Aside from the dubious economics this would entail, this “brand new starter” flour soup likely has a fair bit of seriously questionable bacterial activity still going on and even if it was $8 worth of flour as opposed to the mere 3¢ it more likely is, that stuff really NEEDS to be tossed out. Once your starter has matured, is expanding regularly and consistently and has developed a good, pleasant scent, if it’s ready to be used in bread, then it can be saved for other uses. But until that point, THROW IT AWAY (or put it in the compost). And if you could have smelled Wally in his first couple of days, you would most certainly not want to keep that.

But what about the starter once it’s become viable and working well?

Even after your starter has reached actual starter stage – this will take a week or two – there’s a simple reason why you need to discard your excess. And it is just that, “excess”. After having developed correctly, there’s nothing “bad” about the amount you remove, it’s just as good a starter as what you keep. So if you wanted to, you could give it away to friends who want a ready-made starter or use it in “discard” recipes like pancakes or english muffins or anything else you think the flavour might be a nice addition to. So if it’s just as good as the starter you keep, why not keep ALL of it then?

You really do want to discard. If you were to just keep adding and not discarding any because you “hate to throw anything away”, here’s what you’d end up with in very short order.

One method of feeding says to discard half your starter and add that much fresh flour/water again. We’ll assume we’re basically adding about the same amount of flour+water, so doubling our starter each feed BUT not removing the original half because we “don’t like to throw anything out”. We also keep the starter out and feed twice daily and go one week.

We’ll start on day 1 with a small amount of starter: 2 tablespoons or 1/8 cup. At each feed, we give it an amount of feed equal to the starter, made of 50% water and flour by weight. But for this example, just so we have a better idea of the volume, we’ll assume the volume added is calculated correctly to be by weight, so in that 1/8 cup, there’s, say, 15g flour and 15g water. This is, in effect, a 2:1:1 feeding ratio which is really skimpy on fresh food. If you prefer to do 1:1:1 or 1:2:2, the amounts will increase even faster.

And just for fun

Before you read the rest, take a guess at how much starter you’ll have at the end of one week, starting with just 2 tablespoons and feeding twice a day. Ok, got an amount in your head? Write it down somewhere… No cheating, can’t look at the end or change your mind, now!

Alright, let’s have a look.

• Day 1, Feed 1: we start with 1/8c starter, just 2 tablespoons, so we add 1/8 c of feed so we end with 1/4c of fed starter. Whew, saved from throwing out 1 tablespoon of starer!
• Day 1, Feed 2: 1/4c starter + 1/4c feed = 1/2c total starter. No problem here. Good night, little starter, feed you in the morning!
• Day 2, Feed 1: 1/2c starter + 1/2c feed = 1 cup total starter. Bah, this is easy. Oh wait, our starter is doubling in size so we have to make sure the jar is big enough. So into a quart jar (4 cups) it goes, that should do for a while.
• Day 2, Feed 2: 1c starter gets 1c feed = 2c starter. Hmm. Hope it doesn’t expand past double.
• Day 3, Feed 1: 2c starter + 2c feed = 4c total starter. Well geez, now that quart is full and it hasn’t even expanded yet. OK, into a gallon jug you go.
• Day 3, Feed 2:  4c starter + 4c feed = 8c total. Wow, that’s 2 whole quarts. If it expands to double, this gallon jar will just hold it (hopefully).
• Day 4, Feed 1: 2qt starter + 2 qt feed = 1 gallon total starter. Gah! I need a big bucket for this stuff now. And I just added about 4 cups of flour to this thing. And we’re just barely past the middle of week one. Wonder how long that 5 lb bag of flour is gonna last?
• Day 4, Feed 2: 1 gal starter + 1 gal feed = 2 gal total. OK, into that big 5 gallon Home Depot pail now. Man, I used 12 cups of flour today alone…
• Day 5, Feed 1: 2 gal Starter + 2 gal feed = 4 gal total. Off to the store for more flour…
• Day 5, Feed 2: We now have 8 galons, which need at leasts a 16g container. The kiddy pool would do…
• Day 6, Feed 1: We’re now up to 16 gallons of starter.
• Day 6 Feed 2: 32 gal and you used 192 cups of flour. At ~4.5 oz of flour per cup, that’s  54 lbs of flour in just this one feed, that’s five 10 lb bags and then a bit more… And you’re not quite at the end of week 1…
• Day 7: Feed 1: we now have 64 gal of starter. We better start planning on making bread soon.
• Day 7, Feed 2: 128 gallons of starter. That’s more than your standard bathtub can hold, never mind when it expands. If you want to think about “economy”, you need to ask yourself how much flour you are willing to use to feed this exponentially growing monster., never mind where you’ll be keeping it in a day or two. Maybe the neighbours are away and you can use their pool…

Now let’s keep in mind we began with just two tablespoons. Only about 40 gallons of that is water, the other 80 gallons is flour (water is heavier than flour). That’s SIXTEEN five gallon drums. You will be running to the grocery store and buying out their flour supply in no time. That won’t be cheap.

OR…

You can discard a couple of tablespoons of flour at each feed and keep the starter at a reasonable size for your needs. Whether that’s keeping it to 150g (about a half cup) or a little bigger because you bake a lot. But you’d be a bakery pumping out hundreds of loaves to be using up 128 gallons of starter.

Need a larger amount of starter for your baking day? Take one feed’s discard and build that up to that amount. Or collect a couple days’ excess starter and use it in other baking.

And how close were you in your guess? Go ahead, post it in a comment below.

And what of the future in our “no discarding” scenario? In three more days, you’d have 8,192 gallons. To hold that (and it’s expansion) you’d need a swimming pool 18′ X 36′ X 4′ deep. And the next feed, two of them.

If you were to do your feeding at a better ratio of 1:1:1, you’d have 2,335 gallons by the end of the 7 days.

The preferable 1:2:2 ratio would get you 193 gallons at the end of day four and 2.9 million gallons by end of  day 7.

Now obviously no one would go that far before realizing that NOT discarding is insanely expensive but it may not be obvious how FAST this adds up when you’re looking at your 2 Tablespoons of starter and thinking it’s not worth throwing that extra tablespoon of flour out. Even by about day 4 you’d have got to the point where you’d need to throw out just under 1 gallon of starter to get back to a decent amount, so you’d be tossing at least 7 cups of flour away. Removing 1 tablespoon per feed over that same time is just 1/2 cup of flour.

Which is actually more economical and less wasteful? Which will give you enough extra starter to make pancakes for the family vs pancakes for the local school board?