Contagem de células viáveis em fermento seco.

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Cesar Froener

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Bom dia. Todos sabemos que a quantidade de células viáveis dentro de um pacote de fermento seco é um assunto muito polemico. Se ouve falar em vários números, desde pessoas que contaram, calculadoras e do que o fabricante diz no pacote. Uma coisa é certa, os números são todos muito diferentes, o que aumenta ainda mais a confusão e dúvidas sobre a taxa de inóculo.
Procurando sobre o assunto, me deparei com um fórum em que estavam discutindo sobre isso e vi um comentário de um tal de Eric, que diz ser da Lallermand e achei no mínimo interessante, por isso quero compartilhar com todos vocês para quem sabe abrirmos mais uma vez essa discussão.

Segue abaixo o comentário dele:

"I can speak to this from a yeast manufacturer's perspective.

Counting viable cells for dry yeast is actually not a trivial task. The yeast must be rehydrated prior to counting, so the cell wall undergoes a transition from gel to liquid crystal phase. Typical staining methods can give falsely low readings since the cell wall is more permeable during this time. Automated cell counters can be unreliable since freshly rehydrated cells do not necessarily look like typical yeast cells for which the software was optimized. Plating on nutrient agar is a reasonable alternative, but you must assume that each colony corresponds to a single cell. If cells clump together, it will also result in falsely low viability counts. You can reduce clumping by sonication or a quick turn in a blender, but these methods can also reduce viability...

I have never seen cell counts as high as 20 billion per gram for any dry brewing yeast (Lallemand or otherwise), I would be curious to see the methods used to achieve this. You might see these numbers for baking or wine yeasts where the cells are typically smaller (therefore more per gram), but not for a typical brewing yeast, which is typically 5-10 billion viable cells per gram.

In the end, I would encourage people to not count cells at all when using dry yeast. Simply pitch by measuring the weight of the yeast, 50-100g/hL for most Lallemand ale strains. Pitch rate calculators designed for liquid yeast using a typical 1 million cells/ml/'P do not work very well for dry yeast and usually result in significant overpitching (3-6x the recommended pitch rate for dry yeast). I have a best practice document available for dry yeast viability and pitch rates, send me a PM and I can send it to you.

Or check out the Lallemand Pitch Rate Calculator optimized for dry yeast. These pitch rates are validated by test fermentation after each production to assess lag phase, attenuation, total fermentation time and flavor."

Segue link da discussão no fórum:

https://www.homebrewtalk.com.br/forums/fermentação.163/post-thread
 

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