Why not make a starter with dry yeast?

So I was just wondering earlier - why is conventional wisdom not to make a starter when using dry yeast? What property of dry yeast makes it unnecessary to make a starter (/what property of liquid yeast makes it necessary to use a starter)? I remember reading somewhere once that liquid yeast has a significantly higher cell count than dry (though I think I might have read it on White Labs promotional literature, so that might be totally false), but if that's the case, why does pitching liquid yeast without a starter (especially in big beer) stress the yeast, but not dry yeast?

Some dry yeast has the higher cell count but, no matter what the comparison, it is still less expensive to pitch 2 sachet of dry than a single liquid vial or puff pack.

Secondly, dry yeast is packaged at it's prime ready for growth in wort and has included in the sachet all the necessary minerals and vitamins for minimal stress.

Hydrate and pitch based on OG. I prefer to use 2 packs when approaching an OG of 1.050.

Beats me. I take an empirical approach to questions like this. I always go for the simplest method (reducing my opportunities to screw up). If the simplest method works, I don't try to do anything more.

Simply pitching dry yeast, without making a starter or rehydrating, has always worked. That's enough analysis for me.

If you rehydrate it properly than you should get pretty close to 95% viable and healthy yeast cells. If you do not rehydrate, up to 50% die and you could get off flavors due to underpitching. Dry yeast has reserves built into them and making a starter would use of the reserves and be damaging to the cell. Of course, both ways would work, but you could be making better beer if you do it correctly.

I can't see where there is any problem with a starter with a dry yeast.

I switched to no-chill after just 2 or 3 batches, and used dry yeast until last month (Only because there is no dry belgian yeast).

While the main batch is cooling (usually takes over night) I always put a quart of wort into the freezer for a couple of hours to bring it down to around 70F, and put it on a stir plate with the yeast. 12 hours or so later, I've got a large starter that I dump in the cooled wort.

Usually fermentation usually takes off in just a couple of hours.

t

there is no PROBLEM with doing it, it's just not necessary and increases your costs and time investment.

There are plenty of cells in the packet already. If you make a starter, you spend $5 (or more) on malt extract and add a whole "start making" session to the brew process.

Dry yeast packets have a yeast count of around 20 billion cells per gram. So a typical 11 gram pack has 220 billion cells. As their are dried they are much more tolerant to the extremes in shipping and time sitting on a shelf from their production date. If you rehydrate properly you will get just about all of your 220 billion cells which is enough to pitch for a typical 5 gallon batch.

Meanwhile liquid yeasts have about 100 billion cells and that is immediatelly after production. After some time sitting on the shelf and in transportation you will get some non viable yeast cells, so this is where you yeast started comes in. You are a) checking to make sure your yeast cells survived shipping and any temperature extremes and b) increasing the cell count to get to your pitching rate.