Just a Yeast Thought

[mainshipfred]

Has anyone ever considered adding only say half the recommended yeast dosage? My thoughts are it will allow for a slower fermentation and allow a longer contact with the skins. I would think the yeast should continue to multiply to finish the fermentation. Even if it has a slower start it should give off enough CO2 to initially protect the wine. With proper nutrients I can't see the chances of a stuck fermentation being any higher than a full dose. Never done it before and may try it in the fall unless someone can think of something I'm missing.

 

[salcoco]

minimum dosage is 1 gram per gallon proper hydration will have a good yeast colony. as cheap as it is what is the benefit of risking a stuck fermentation.

 

[1d10t]

With beer the amount of yeast to pitch is well studied. Over pitch and the yeast will enter the anaerobic cycle too early and not produce the proper amount of esters producing less flavor. Too little and they become stressed and produce off flavors. No idea if this applies to wine.

 

[mainshipfred]

The reduced dosage is to let the fermentation last longer for more extraction. Are you saying the yeast will stop multiplying at a certain point?

 

[salcoco]

once the sugar is gone no more fermentation.

 

[Johnd]

Has anyone ever considered adding only say half the recommended yeast dosage? My thoughts are it will allow for a slower fermentation and allow a longer contact with the skins. I would think the yeast should continue to multiply to finish the fermentation. Even if it has a slower start it should give off enough CO2 to initially protect the wine. With proper nutrients I can't see the chances of a stuck fermentation being any higher than a full dose. Never done it before and may try it in the fall unless someone can think of something I'm missing.

My understanding is that the yeast will reproduce continually until a properly sized colony exists to handle the amount of sugar in the must......the lag phase, then it starts working on the sugar....Alcoholic Fermentstion. Shorting the amount of yeast in the beginning may only serve to lengthen the lag phase, not the length of AF.

This is only my layman’s simplistic understanding of the process. I bet @stickman could weigh in here with some more solid information.

 

[CDrew]

I don't think it will make much difference. If you pitched say 1/2 the amount, you're only 1 doubling cycle away from a normal pitching amount. Doubling time for yeast growth is 90 minutes(a rough estimate but quoted). So at most you'll lengthen your fermentation by 90 minutes. But it does give 90 more minutes for spoilage organisms to get established. My vote is to pitch standard amounts of yeast. If you want fermentation to take longer, cool down the must to a lower temperature.

 

[stickman]

With very clean fruit a lower pitch rate is ok, but several things have to be considered. Normally the pitch rate is designed to provide a 100 fold size colony of the desired yeast, meaning the cell count of the desired yeast is 100 times any existing yeast population. If your colony is less than this, the desired yeast has a reduced chance of dominating the batch, so the yeast manufacturers always recommend a high pitch rate. Given the number of reproduction cycles required with low pitch rates, nutrients and aeration during the growth phase becomes more important, but I'm certain you'll do fine there. Several studies a few years ago showed that during a cold soak, the ambient yeast start to acclimate in the must, and by the time the normal dose of cultured yeast was added, the cultured yeast cell count was not adequate to dominate the fermentation. The recommendation at the time was to add 1/10 the normal pitch rate at the start of the cold soak to allow acclimatization and provide competition against the ambient yeast, then once temperatures increase, another dose of cultured yeast would be added.

The fact that uninocculated musts with fairly low cell counts will ferment to completion, indicates that any pitch rate will do, you just wont know with a high degree of certainty what yeast dominated the batch. For a number of years I used to ferment 500 lbs of must with a single packet of yeast, but I always made a starter to build up the culture before pitching. That method worked and AF went to completion, but I felt some of the fermentations were stressed near the end, so I switched to using normal recommended pitch rates. For low pitch rates, clean sorted fruit is important to ensure low initial cell counts of undesirable organisms.

 

[salcoco]

reviewing your initial post, if you intend is to increase the influence of the skins in your wine either color retention or tannin among other, do a cold soak at the beginning maybe three days before adding yeast. enzymes can be added to improve color extraction. there are also techniques post fermentation to increase color and body. I would investigate these techniques rather than short the yeast.

 

[Boatboy24]

My thinking is that the slower your desired yeast achieves a proper sized colony, the better chance some other organism has of taking hold. Agree with Sal that a cold soak and/or enzymes would achieve the desired result in a safer way.

 

[Rice_Guy]

* To your original post, the easiest way to slow fermentation is to decrease temperature. The extraction rate of skins will decrease as the temp is decreased so we are looking at balancing metabolic activity vs chemical extraction rate. In general chemical processes double for every 10C increase.
* @stickman did a good analysis of yeast growth. The competing populations will grow till the resources they are optimized for are consumed. Then another population will come in which has different metabolic requirements. ,,, ie for the purpose of slowing a fermentation there will be no difference. (A food example of this is that yoghurt has a preliminary 120F sugar fermentation producing acid, followed by a proteolytic fermentation which creates bitter flavors. I could skew the fermentation by giving a sub optimum condition as dropping the temperature to where psychrophyles dominate the primary fermentation.)

The universities have done quite a bit of research on optimizing extraction from the skins. I would follow their lead.

 

[mainshipfred]

Thanks all, guess I'll scrap the idea.

 

[DizzyIzzy]

With very clean fruit a lower pitch rate is ok, but several things have to be considered. Normally the pitch rate is designed to provide a 100 fold size colony of the desired yeast, meaning the cell count of the desired yeast is 100 times any existing yeast population. If your colony is less than this, the desired yeast has a reduced chance of dominating the batch, so the yeast manufacturers always recommend a high pitch rate. Given the number of reproduction cycles required with low pitch rates, nutrients and aeration during the growth phase becomes more important, but I'm certain you'll do fine there. Several studies a few years ago showed that during a cold soak, the ambient yeast start to acclimate in the must, and by the time the normal dose of cultured yeast was added, the cultured yeast cell count was not adequate to dominate the fermentation. The recommendation at the time was to add 1/10 the normal pitch rate at the start of the cold soak to allow acclimatization and provide competition against the ambient yeast, then once temperatures increase, another dose of cultured yeast would be added.

The fact that uninocculated musts with fairly low cell counts will ferment to completion, indicates that any pitch rate will do, you just wont know with a high degree of certainty what yeast dominated the batch. For a number of years I used to ferment 500 lbs of must with a single packet of yeast, but I always made a starter to build up the culture before pitching. That method worked and AF went to completion, but I felt some of the fermentations were stressed near the end, so I switched to using normal recommended pitch rates. For low pitch rates, clean sorted fruit is important to ensure low initial cell counts of undesirable organisms.

Stickman.....I have a receipe for banana wine which calls for simmering crushed bananas and skins in boiling water, then straining into a primary. Is there a reason why I couldn't also add crushed bananas in a straining bag and leave in primary (with thoughts of increasing the banana flavor) during fermentation?

 

[stickman]

@DizzyIzzy My experience is primarily with wine from grapes, so it's probably better if I stand back and let other members, more experienced with banana wine, comment.