Here's a saibara song called "Inside this mansion" (此殿奥):

Kono tono no, oku no, oku no sakaya no, ubatamari,
Aware, ubatamari, hare,
Ubatamari, ware o, ware o kou rasi, kosakagoe naru ya, goe naru ya.

The brewery inside, inside this mansion, where the matrons gather,
Oh! where the matrons gather, yes!
The gathered matrons want me, want me, so it seems, with their strong sake voices, oh! their voices!

Kimura Noriko, editor of the book I found this in, notes that we have no other contemporaneous attestations of the word uba in this sense, but it seems fair enough to assume that it means "old woman" (for historically appropriate values of "old", of course), same as it did in later times. What I have translated "strong sake voices" is in the original a compound word: kosakagoe, from ko- ("strong, rich") + saka- ("bound form" of sake) + rendaku'd koe ("voice").

(Kosake was a type of strong, sweet sake that you could make overnight; this page describes it as "commoner's sake". We aren't talking about high society ladies working in the brewery here.)

It's interesting that "voice" appears in rendaku'd form as goeon the next line too, even though there the kosaka- part isn't repeated. Well, it's interesting to me.

One final note: Kimura suggests that chapter 63 of the Ise monogatari may contain a reference to this song:

Momo tose ni/ hito tose taranu/ tsukumogami/ ware wo kou rasi/ omokage ni miyu
The lady with thinning hair—/ But a year short/ Of a hundred—/ Must be longing for me,/ For I seem to see her face. (English translation: McCullough 110)

Bibliography

• Kimura Noriko 木村紀子, trans. and ed. Saibara 催馬楽. Tokyo: Heibonsha, 2006. Print.
• McCullough, Helen Craig, trans. and ed. Tales of Ise. Tokyo: University of Tokyo Press, 1968. Print.