1) From my experience.
2) From Viginia Tech
: "in general 1 ton of harvested grapes produces 100lbs of stems and 160 to 240 lbs of pomace
...". So, since I said and referred only to "destemmed grapes", so one can ignore the 100 lbs of stems. And if one takes 1 ton =2000 lbs, average of 160 and 240 is 200 lbs, and 200 is 10% of 2000, so 30 lbs expected from 300 lbs.
Thanks for the additional detail - this helps me to see where I've been off in my estimates. For red wine, alcohol is lighter than sugar, so the weight of the escaping CO2 also needs to be taken into account.
Also, if the virgina tech estimate is 5% of weight for stems, that's good enough for me and I will replace the 10% estimate I've been using.
For commercial wineries, the lower amount of pomace is probably realistic, but for small home winemakers, the larger figure of 240 lbs probably makes more sense.
So my revised estimate:
316 lbs of grapes
300 lbs / 35 gallons of must (8.57 lbs / gallon of unfermented juice)
38 lbs of pomace (240/2000 x 316) filling ~12 gallons (3 lb / gallon
23 gallons of wine weighing ~191 lbs (8.3 lbs/gallon)
weight of fremented sugar & released CO2: ~70 lbs [300 - (191+38)]
So I'm now within ~20% of your estimate and if I assume that a bladder press will press the must dryer and result in 200 lbs of pomace per 2000 lbs of grapes, I get 31.6 lbs of pommace (and either a higher volume of wine pressed out or a larger weight lost to sugar and CO2).
I'm a little confused by the weight / gallon of pommace - I would have thought it was denser than wine and would sink...
I will add a tiny correction: one gallon of water weights about 8.35 lbs, but grape juice also has quite a bit of sugar in it too so will be closer to 9 lbs per gallon so expect about 700 lbs for the 78 gal of juice. That leaves 300 lbs for pumace, versus 200 Virginia Tech averages and not too far from the upper range of 240. So the two results are "close enough", in my humble opinion, and you can go with your calculation since your numbers are based on your experience which counts a lot (and anyway, always better to over estimate a bit here, after all, you will be the one lifting it).
Accounting for weight lost to sugar and CO2, I'm pretty comfortable that 30-40 lbs of pomace for 300 lbs of must looks reasonable (though would love to hear from anyone with an 80-90 liter bladder press - how much does the pomace 'tube' after pressing a full 300 lbs of must weigh?
Does he use the bag insert?
pretty sure he does - I believe it was the weight and unwieldiness that was the issue, but will check.
If not, then, yeah, getting grape squish out of the tiny slits is not fun (especially if there was any drying of the grape skins and squish on the basket (then get out your hammer and chisel**), which can happen if one does sequential loading). But those issues will be true of any of the bladder presses as they use similar basket designs. Best practice, for easist cleaning, is to press, immediately empty, clean (hose down well, minor brush work if needed), then reassemble and reload fresh, then press again.
What do you mean by 'squish' on the basket? Dried grape skins attached to the insides of the basket?
I see MoreWine claiming that 45 minutes is a typical press clcle time with both the 40-liter and 90-liter Speidel bladder presses, while Lancman claims a 15-minute press cycle time for essentially all of their presses (40 & 80-liter fixed; 80 & 120 liter tilting). I would appreciate to hear from anyone with experience with any of these bladder presses to comment on what cycle time they believe is realistic for a single-handed operator.
But, for transparency, my experience with the bladder press is limited to larger units (over 200 l) and to pressing and intermediate cleaning (as described above which left a pretty clean basket) to see if I should get one to replace my 200 l basket press (now there is something really fun to clean all by oneself....). But I do not own a bladder press myself, at this time yet, and have not done a "work is done" cleaning getting everything out of all hidden nooks and crannies.
** I am being a little facetious. But just a little.
I'm kind of in your same shoes and appreciate your perspective. My #50 basket press works well to press up to a quarter-ton of grapes in one run, but cleanup is a bear.
My primary motivation for a bladder press is greater control over press lots and hopefully more tannins out of my skins.
But it seems as though one tradeoff with bladder presses is faster/easier cleaning at the cost of being smaller (meaning multiple press runs).
An 80-liter tilting Lancman bladder press costs twice as much as a 40-liter fixed bladder press. For 900 lbs of grapes / 100 gallons of must, we're probably talking about 3 press runs in the 80-liter versus 6 in the 40-liter.
If it's 45 minutes per run and that translates to 2-1/4 hours versus 4-1/2 hours, the 40-liter doesn't seem like a very attractive option (despite the savings).
But if 15 minute press runs are realistic and the difference is 45-minutes versus 90-minutes total, the 40-liter press may be worth considering.
My suspicion is that 15-minutes is for 'as fast as you can go' single-lot pressing (such as when pressing apples), and I plan to make press lots in 0.1 bar increments after 1.5 or 2 bar. So if your planning for press lots, fewer press runs is probably the only viable way.
Any inputs from those with experience with these 40-80-90-120 liter bladder presses appreciated.