"Hi ratflinger,
Originally Posted by: ratflinger 
Can you elaborate? I have a sugar & a tomato paste in separate fermenters now, just to see if there is a different rate of conversion. If there is it isn't much. I wouldn't think there'd be much of a taste difference in the end, since both have heavy nutrient additions.
I'll take a stab at this.
I started using tomato paste (BW recipe) out of pure laziness -- I was doing All Bran recipes and had to make my own trips to the store to make sure I'd get the stuff with the nutrients I wanted (they're not all created equal). My wife doesn't want to be bothered reading labels, but she is always buying tomato paste so it's always available and she'll pick up a spare case for me. I married well.
In any case, I started to wonder what the tomato paste (and Mg) provided ... so I did a little research. This is what I learned:
Tomato paste is a source of potassium (Vitamin K) and various B-vitamins, specifically, Vitamin B3 (Niacin), Vitamin B5 (pantothenic acid), and Vitamin B7 (Biotin). It can also include some calcium. The actual concentrations of these are dependent on the types of tomatoes used (and the processing of them). The value of these vitamins I got from wikipedia:
Vitamin B3 - involved in the synthesis of Nicotinamide adenine dinucleotide (NAD+), a co-enzyme that is important in maintain the redox balance of the cell as well as in the process of ethanol fermentation itself.
Vitamin B5 - involved in the metabolism of sugars and lipids. A deficiency of this vitamin could lead into increase hydrogen sulfide production with off-aromas in the resulting wine.
Vitamin B7 - involved in the synthesis of proteins, fatty acids and nucleic acids.
Vitamin K - important for the uptake and utilization of phosphate. Phosphate is used for the production of nucleic acids, phospholipids (an important component of the cell membrane) and ATP (Adenosine triphosphate which the cell uses for transferring energy for metabolism)
The calcium (which may or may not be in significant concentration in the tomato paste) and the epsom salt (for magnesium) do a few things. The first is that both support cell metabolism. The second is that they both enhance ethanol tolerance. The magnesium also protects yeast cells from stress caused by temperature and osmotic pressure. There are several papers on the web that describe all of this. An interesting note is that calcium and magnesium can work against each other.
All that said, whether you get any significant benefit from the tomato paste will depend on a lot of factors: water chemistry, wash gravity, fermentation temperatures, yeast strain (and whatever nutrients are packaged with your yeast), the type of wash itself (refined sugar only, a grain wort, a sugarhead), pH, etc. etc. One thing is certain though: refined sugar and water by themselves don't contain all of the components of a well-balanced diet for yeast cells. That doesn't mean they can't multiply, grow and ferment the wash dry ... just that they may be eating too many twinkies.
So there's a potential for slow or incomplete fermentation as well as an increase in by-products.
I did perform a few experiments using my tap water and just sugar and found that I could not get the wash to finish below SG 1.000. With some source of nutrients like bran flakes (the proper kind), tomato paste, DAP, etc. the washes would always finish below SG 1.000.
Given the information I could find on this ... and that I don't use turbos, I came to the conclusion that a $0.55 can of tomato paste certainly didn't hurt anything and as a minimum, served as a sort-of insurance policy. So when I'm not playing around with grains (which I'm still not very good at) my go-to recipe for my neutrals/vodka runs is Birdwatcher's (water, sugar, tomato paste, lemon juice and some epsom salt).
Regards,
--JB"
