Mishnah Taharos 2:8: One who is eating foods of a second degree [impurity] should not work in an olive press [since his body becomes of a second degree, and he then renders liquids impure]. And non-sacred foods that were prepared with the stringency of sacred foods still follow the rules of non-sacred foods [i.e. unlike sacred foods, they cannot be rendered third degree by a second degree impurity, nor are they rendered fourth degree by a third degree impurity]. Rabbi Elazar bar Rabbi Tzadok says: In fact they are like terumah, in that [if they touch an origin of impurity] two are rendered impure [those rendered of a first and second degree impurity] and one is invalidated [that of a third degree; and it does not produce a fourth].

הָאוֹכֵל אֹכֶל שֵׁנִי, לֹא יַעֲשֶׂה בְּבֵית הַבָּד. וְחֻלִּין שֶׁנַּעֲשׂוּ עַל גַּב קֹדֶשׁ, הֲרֵי אֵלּוּ כְחֻלִּין. רַבִּי אֶלְעָזָר בַּר רַבִּי צָדוֹק אוֹמֵר, הֲרֵי אֵלּוּ כִתְרוּמָה, לְטַמֵּא שְׁנַיִם וְלִפְסֹל אֶחָד:

Mishnah Taharos 3:1: Sauce, ground beans, and milk, when they are a liquid and able make other things wet, [they are considered liquids such that] they are [made] primary [i.e. of a first degree level of impurity, if they become impure]. If they congeal, they are [able to become] of second degree [like foods in general]. If [when impure] they were then re-softened [into liquid], if there is exactly the equivalent of an egg [in volume] of them, they are pure [since they lost their impurity status in shifting states]; if there is more than the equivalent of an egg [in volume] of them, they are impure, since once the first drop came out [and softened into liquid] it was rendered impure by the [remaining] egg's volume [which is a sufficient amount of food to render impurity, and the rest of the food, as it softens, is rendered impure by that impure liquid, since liquids of any amount can be rendered impure; but when there is exactly an egg's volume of food, the first drop of it that softens into liquid is not rendered impure by it, since there is not a sufficient measure of food left there to render it impure, since foods are only rendered impure and render impurity when there is at least an egg's volume of them].

הָרֹטֶב וְהַגְּרִיסִים וְהֶחָלָב, בִּזְמַן שֶׁהֵן מַשְׁקֶה טוֹפֵחַ, הֲרֵי אֵלּוּ תְּחִלָּה. קָרְשׁוּ, הֲרֵי אֵלּוּ שְׁנִיִּים. חָזְרוּ וְנִמֹּחוּ, כַּבֵּיצָה מְכֻוָּן, טָהוֹר. יוֹתֵר מִכַּבֵּיצָה, טָמֵא, שֶׁכֵּיוָן שֶׁיָּצְאָה טִפָּה הָרִאשׁוֹנָה, נִטְמֵאת בְּכַבֵּיצָה: