This post is a summary of a shiur (my understanding) of a shiur of Rabbi Ezra Schochet on the zoom yarchei kallah for 20 Av.
Rambam Laws of Brachos (1:2)
וּמִדִּבְרֵי סוֹפְרִים לְבָרֵךְ עַל כָּל מַאֲכָל תְּחִלָּה וְאַחַר כָּךְ יֵהָנֶה מִמֶּנּוּ. וַאֲפִלּוּ נִתְכַּוֵּן לֶאֱכל אוֹ לִשְׁתּוֹת כָּל שֶׁהוּא מְבָרֵךְ וְאַחַר כָּךְ יֵהָנֶה. The Alter Rebbe's Shulchan Aruch (167:1) echoes this ruling
מִצְוַת עֲשֵׂה מִן הַתּוֹרָה לְבָרֵךְ אֶת ה' אַחַר אֲכִילַת מָזוֹן, שֶׁנֶּאֱמַר "וְאָכַלְתָּ וְשָׂבָעְתָּ וּבֵרַכְתָּ אֶת ה' וְגוֹ'". וּמִדִּבְרֵי סוֹפְרִים לְבָרֵךְ לִפְנֵי כָּל אֲכִילָה וּשְׁתִיָּה. What is noteworthy is why the change in terminology from עַל כָּל מַאֲכָל as the Rambam said, to the words לִפְנֵי כָּל אֲכִילָה וּשְׁתִיָּה that the Alter Rebbe chooses? Furthermore, the Rambam's words would seem to be more precise for the word אכילה means a כזית as the Alter Rebbe himself writes in 184:2
וּמִדִּבְרֵי סוֹפְרִים לְבָרֵךְ בִּרְכַּת הַמָּזוֹן עַל כַּזַּיִת, שֶׁהוּא שִׁעוּר אֲכִילָה, אֲבָל פָּחוֹת מִכַּזַּיִת אֵינָהּ נִקְרֵא[ת] אֲכִילָה כְּלָל, and one is obligated to say a beracha before eating even on less than a כזית (as the Rambam and Alter Rebbe 168:7 say)?
To explain why the Alter Rebbe switched from the Rambam's terminology we can say they are going לשיטתם as to what creates the obligation of a beracha. The Rambam holds that anything that is a food obligates one to say a beracha before eating it. Other Rishonim and the ruling of the Alter Rebbe is that one is only obligated for a normal form of eating/drinking. This machlokes is illustrated by a few examples.
1. The Rambam (8:7) based upon Berachos (36b) says
הַפִּלְפְּלִין וְהַזַּנְגְּבִיל בִּזְמַן שֶׁהֵן רְטֻבִּין מְבָרֵךְ עֲלֵיהֶן בּוֹרֵא פְּרִי הָאֲדָמָה. אֲבָל יְבֵשִׁין אֵין טְעוּנִין בְּרָכָה לֹא לִפְנֵיהֶם וְלֹא לְאַחֲרֵיהֶם מִפְּנֵי שֶׁהֵן תַּבְלִין וְאֵינוֹ אֹכֶל. The Rambam says there is no beracha only because pepper and ginger aren't defined as foods. The Alter Rebbe (202:22) brings the reason of Rashi and other Rishonim that there is no beracha because its not considered fit for consumption, אֲבָל פִּלְפְּלִין יְבֵשִׁים וְזַנְגְּבִיל יָבֵשׁרמג וְכֵן הַצִּפֹּרֶן (שֶׁקּוֹרִין נעגלי"ך), וְכָל כַּיּוֹצֵא בְּאֵלּוּ שֶׁאֵין נֶאֱכָלִים בְּיֹבֶשׁ אֶלָּא עַל יְדֵי תַּעֲרֹבֶת – אֵין מְבָרְכִין עֲלֵיהֶם כְּלוּם כְּשֶׁאוֹכְלָם בִּפְנֵי עַצְמָם,
שֶׁאֵין זוֹ אֲכִילָה שֶׁל הֲנָאָה לְבָרֵךְ עָלֶיהָ בִּרְכַּת הַנֶּהֱנִין. Even if they were considered an אוכל, food, there is still no beracha for there is not the normal way to eat these things.
2. The Gemorah (35b) says that drinking olive oil straight is not beneficial for the body. The Alter Rebbe (202:10) holds that there is no beracha said. However, The Rambam (8:2) rules one must say a שהכל. Why, if it is not beneficial at all? The Kesef Mishne says because there is still pleasure in drinking it. That reason is contradicted by the Meiri that says there is no pleasure at all from drinking olive oil. The reason of the Rambam may be explained with a Rabbenu Yonah (28b in Rif cited in Beis Yosef 204:1) that says even though drinking vinegar is not considered drinking to be prohibited on a fast day, since one is obligated for eating on Yom Kippur if they drink an amount of רביעית, therefore, in regard to a beracha as well it is still considered a food. The Bach (204:4) says that is the explanation why the Rambam holds there is a beracha on olive oil. We see again, even though it is not the normal way of eating, since it's defined as an אוכל it is obligated in a beracha. However, the Alter Rebbe goes like the other Rishonim that one is obligated only for eating something that one benefits from. Hence, the Alter Rebbe doesn't say one is obligated to say a beracha on every מאכל like the Rambam, for he holds that being an אוכל doesn't obligate one in a beracha unless it's a normal form of eating, אכילה ושתייה.
That explains why the Alter Rebbe deviates from the language of the Rambam. However, we still need to understand how what he said is true, what happened to the rule of אין אכילה פחותה מכזית? The Rambam at the end of 1:2 says
וּמַטְעֶמֶת אֵינָהּ צְרִיכָה בְּרָכָה לֹא לְפָנֶיהָ וְלֹא לְאַחֲרֶיהָ עַד רְבִיעִית: The Kesef Mishne explains because there is no intent to eat -
ואפשר לתת סמך לדבר דטעמא משום דכתיב ואכלת וברכת שיהא לו כוונת אכילה משמע. This is מדיוק in the beginning of the Rambam where he says
נִתְכַּוֵּן לֶאֱכל אוֹ לִשְׁתּוֹת כָּל שֶׁהוּא, there is כונה to eat. But what does that mean, how can there be כונה to eat if אין אכילה פחותה מכזית? What we see is the rule of אין אכילה פחותה מכזית doesn't mean that is not considered a מעשה אכילה, that it's like eating something that's nor דרכו לאכול. Rather, there is a מעשה אכילה that was done to the food, but it's not considered as if the person ate. With this idea we can also explain some Achronim that hold one is obligated in ברכת המזון even if one didn't eat a כזית in the amount of time of כדי אכילת פרס or the חת"ס holds even for less than a כזית if one is satiated one is obligated. How can this be in the Torah says ואכלת? Because they hold its enough that a מעשה אכילה was done that made the person satiated, one is obligated even though it's not considered as if the person did a מעשה אכילה.
The Minchas Chinuch (430:2) learns that you need an אכילה to be obligated in birchas hamazon so if one ate for example שלא כדרך אכילה there is no obligation. He has a doubt if one ate a כזית normally and the additional amount to add up to כדי שביעה was שלא כדרך אכילה if there is a תורה obligation of birchas hamazon or the entire שביעה must be done through normal eating. The Minchas Chinuch equates שלא כדרך אכילה with a כזית not eaten בכדי אכילת פרס. According to this lomdus, even if you need the entire שביעה to be through אכילה, a כזית not eaten בכדי אכילת פרס, in other words, אכילה פחותה מכזית will be considered a מעשה אכילה to add to the original כזית to make one obligated in birchas hamazon.
Based upon this we understand why it is true what the Alter Rebbe writes לִפְנֵי כָּל אֲכִילָה וּשְׁתִיָּה because even with less than a כזית it still is a מעשה אכילה of the food.
