Taste and Smell
Many new technologies suffer lack of acceptance because of erroneous and preconceived opinions, rumors, and tradition. Pasco Poly deals with it on several fronts. Rumors abound about plastic odors, temperature stratification in tanks, air heating and cooling of tanks, pump under fermentation process, and suction pressing of wine.
With respect to the tastes and oxygen permeation in wine tanks, we resolved this issue before starting the poly wine tank manufacturing business.
We commissioned a study to canvas wineries and find their tank needs and concerns.
Being in the early 80's, there was a lot of talk of air permeation of polyethylene milk jugs, so the “air permeation of wine” issue automatically came up. I guess it must not have been a valid issue with milk bottles. I have not seen any change there.
Because of the air permeation issue I did a test to find out about this.
In the early 80's I spoke with Roger Boulton of U.C. Davis, when he was speaking at a winemaking conference in Yakima Washington, asking about how to duplicate wine conditions to check on the permeation of oxygen. He suggested Tartaric acid, vodka, and boiled water.
I built two identical 5 gal tanks, which, by their small size would provide very high tank wall area/gallon ratio. One was built of stainless steel, and one was built of polyethylene.
Filled them with identical batches of vodka, boiled distilled water. and cream of tarter.
Put them in a refrigerator at 45 deg. (cold liquid can hold more oxygen than warm), and monitored their temperature and oxygen content for some months. I found little difference between them, but toward the end of the test I did discover drastic stratification of temperature and oxygen content. It was quite surprising to see the amount of temperature stratification in such small tanks. It was not surprising to find no difference in the oxygen content even at that low level, but the oxygen stratification was a shocker. Unable to do a more definitive study on oxygen stratification we never made an issue of that.
The big issue was however TASTE and SMELL of “Plastic”. The noun “plastic”is so general, pertaining to such a broad spectrum of materials, we have to be quite specific.
Thermally formed polyethylene (FDA approved for the purpose) in an inert atmosphere at proper molding temperatures, leaves no residue of taste, smell, or substance in wine.
There is a recent issue of plastic residue in poly carbonates and poly vinyls which appear to be real concerns. However, that issue is not with polyethylene. I just have not heard a record of smells or tastes, or modification of wine, from polyethylene at wine tank temperatures, or for that matter, at higher ones.
The Old Wives Tale
“Plastic makes your wine stink” can be applied to most cross-linked and fiber glass “plastic tanks.”
So many variants of plastic tanks have been absconded, salvaged, adapted, and homemade that there is a rich rumor mill of taste and smell experiences with “plastic” tanks .
The worst offender is high grade crosslinked polyethylene ag tanks. These tanks are tough and smelly, except for some produced by very modern and expensive processes. The next offender is “run of the mill” fiberglass tanks (with two-part epoxy) which are highly dependent on the laborer and raw materials to keep foreign tastes, contaminants and smell, and flora under control. Some of these can be very difficult, or impossible, to clean because of poor control of porosity.
We have had, in my memory, two complaints on plastic odor being in wine, over the last 20 years and thousands of tanks. One complaint came from a lawyer's son who stored 120 gallons of his white wine in a 500 gallon tank, and said the off-taste was “obviously due to the smell of the polyethylene tank.” The second concerned a 250 gallon tank in Canada that we replaced, although we were positive that the tank was really not the cause there, either. There may be others out there with some doubts, but I have not heard of them.
There is some issue with upper manways, and issues related to their maintenance, but this is not a polyethylene taste issue, and is very likely to be winemaking and tank maintenance issues rather than polyethylene taste issue.
All I can say about taste and smell is that after millions of gallons of Pasco Poly and PolyVin polyethylene tanks, over 20 years of use, there has not been reason to be an issue, and it has never shown to be an issue. We pre-purge and post-purge our molds and tanks with nitrogen gas and carefully monitor the end product for off odors, over-heating or under-purging. All of our molding machines have operational nitrogen injection systems.
Our larger tanks, especially the 4300, has
very low side-wall area per gallon ratio, and is even less likely to
be a problem than with a 5 gal bucket or jug. ©
Pasco Poly inc.