Losing too much liquid during sous viding

You shouldn't have to sear anything first. What time and temperature are you using to cook them at? And what kind of meat is it? Liquid loss from the food is pretty common, there's not much you can do because it's part of the cooking process.

The moisture can come from wet meat and meat juices. I don't think there is much you can do about wet meat, although the liquid is more likely to be water. I'm pretty sure that the amount of meat juice pushed out from the meat is a function of temperature ie the higher the temperature the more the meat fibres contract forcing juice out of the meat.

One thing to keep in mind is that all cooking methods are going to pull water out of meats. But, many of these methods hide the actual amount. If you are roasting, the majority of the water is evaporated (but remember that it would be impossible to make gravy without these juices escaping. That also is lost flavor unless you capture and do something with them). Grilling.... it just drips and evaporates when it hits the coals.

If you browse around on the net, there is a fellow (sorry, don't remember the site) that tried pre-searing before cooking and post-searing and his tasters couldn't tell the difference.

But ultimately, it is a matter of whether you enjoy what you've cooked. Now, small changes in temperature can have significant effects on your recipes. For example, I first started cooking beef tenderloin steaks at 137F, as recommended by the card that came with the Sous Vide Professonal from PolyScience. Everyone thought they were very good. At this temperature, there will be (in my experience) no red juice when I cut the steak. Cooking a steak (most recently, a sirloin roast) at 134F resulted in a wonderful medium rare but I now had juice on my plate as I cut the steak. Both of these temperatures had meat juice in the bag from cooking, and I don't know that there really was a significant difference in the amount... But lower temperatures will result in jucier cuts of meat.

Experiment and see what you enjoy.

Although we want to form a crust to normally add taste and color, I seem to remember reading a pre-sear has the additional benefit of killing any surface bacteria. My question is, is this required or does it depend on the type of meat being cooked?

The pre-sear does kill any surface bacteria but the sous vide process will also kill them, or the post sear will as well so it's not required, and the flavor benefits of the pre-sear are also generally thought to be minimal. I personally never pre-sear my meat.

I recall that in taste tests conducted at FCI, pre & post searing SV-cooked meat resulted in the best flavor. I find pre-searing does work very nicely for chicken.

Yeah, the merits of the pre-sear are interesting. Some people swear by it, the Serious Eats people did blind tests and no one could tell the difference, and the FCI seems to think it helps (at least when they did their article).

I'd say if you think it helps then there's definitely no harm in doing in!

Searing makes no difference to liquid loss at all, it is simply a flavour thing. I've just tried brining beef as per another post on this site. I noticed a considerable reduction in the liquid loss from this batch so no idea if that could be a solution. Can't think for the life of me why it would lose less liquid but it certainly seemed to.

I get conflicting ideas on cook time. I read "the longer you cook it the drier it becomes" and I read that dryness is related only to temperature. For a tougher steak. I want to cook it longer to tenderize it.. But too long will toughen it ? I did a sirloin tip steak for 4 hours.'it was tender but a touch dry (138dg). 1 hour was rough. Don't really want to waste all that time and money in testing. Or should I only worry about cooking these meats for 10-12 hours !

My prob also. Even at 38*C too much liquid. Some meat doesn't bleed much at all. I think that some wet aged meats seem OK. I notice on this site's vids. there is little if any liquid.
So I ask, would the use of cry-o-vac bags (to wet age in fridge) over come this problem, and if so can I sv in these bags.?
Otzi.